Author Topic: Fuel Gauge Connected Directly To Sender  (Read 15710 times)

Pawel66

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Fuel Gauge Connected Directly To Sender
« on: November 06, 2020, 18:46:18 »
My question and request for help is:

If I connect a fuel gauge right at the sender (fuel gauge supposedly matching the sender), will it show correct reading? Mine is showing full while there is less than half of tank of fuel.

I took the plus and signal from the sender right in the trunk - I wanted to check if the gauge works before getting behind the dash. And it shows wrong reading.

Is there a resistor in the instrument cluster that makes it necessary for gauge to work correctly? Or SLS sold me a wrong gauge?

There is a resistor on the wiring diagram, but there is a resistor in the gauge assembly. Or it is another one in the instrument cluster?
Pawel

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Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #1 on: November 07, 2020, 10:30:28 »
I found these remarks, but not commented further:

https://www.sl113.org/forums/index.php?topic=11540.msg77484#msg7748

So I remain with my question: is there a resistor or other component inside the instrument cluster that would affect fuel gauge reading?

Enclosing two more pictures I found on the Forum and ebay. I see connecting plates to fuel gauge, but do not know if there is any component between them and wires coming in.

Again, I see resistor on the wiring diagram. Buy I also see a resistor inside the gauge assembly - I do not know if this is the same resistor as on the diagram or there is another one in the cluster.
« Last Edit: November 07, 2020, 11:23:29 by Pawel66 »
Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #2 on: November 07, 2020, 11:53:07 »
Subscribing here. Ive replaced both the sending unit, and gauge, and still have erratic results (gauge jumps all over the place). I would take the gauge I took out, and wire it up in the trunk, and start the diagnosis from there, if your able to confirm that it can be done. Ive lived with this for 2 years, as after replacing everything, and it still didnt work, I had to step away....

lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #3 on: November 07, 2020, 12:47:37 »
Dear Pawel

These are the challenges I like to solve.

There is always a work around to fix these but implies been analytical.

The wiring from the trunk to the instrument cluster is indeed a resistance, as you know electricity drops voltage as it travels trough cables.

In the case of a fuel sender unit and the fuel gauge at the instrument cluster, the thing works like these.

We have a positive T15 feed directly to the gauge.  And on the other hand we have a negative variable signal coming from the fuel sender. The weaker the negative signal is the lower the fuel gauge will mark on the cluster.

There are two values of resistance given by your fuel sender that have to be noted. One with the tank full measured in OHM and another with tank empty also in OHM. The value for a full tank of the resistance should be lower than the value for empty.

Years pass over our wiring harnesses and values vary a lot since many connections are corroded or loose making the resistance values higher than original.

The first approach will be to polish and sand each of the individual connectors involved in the path of ground travel from the fuel sender to the fuel gauge.

Will come soon with another approach. Let me study some before.....

Best regards
Lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #4 on: November 07, 2020, 13:44:04 »
Take the sender out of the tank, plug it into the connector to the gauge and manually move the float up and down to see how the needle responds. This simple test will demonstrate if the electricals are working properly or if the problem lies with a malfunctioning float.

Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #5 on: November 07, 2020, 16:41:59 »
Thank you for your kind attention!

Lpetersen - the topic of increased resistance crossed my mind, but I would have thought that the resistance of wiring between where sender is and the instrument cluster is negligible unless there is some resistor in the instrument cluster, other than the one in gauge assembly itself.

The history is as follows:
1. Some years ago I had the old type of float and gauge - they were working properly and accurately.
2. I wanted to have a system that 280SL had - tube type sender and corresponding gauge.
3. I bought a new sender at MB and installed it.
4. I bought a second hand from a vendor who promised it was from W113.

But I do not think it was a W113 gauge - it showed 1/4 of tank less relatively consistently from full to empty. If filled full, gauge showed 3/4, etc.

I bought W113 late gauge form SLS. Before diving under dash I wanted to check it. I hooked + from fuse box, signal form corresponding pin in the sender and left ground connected to the sender from the harness (brown wire). The tank is 1/3 full. But the hand pegs at 4/4. I see 2 possibilities:
1. Something is wrong with the gauge.
2. The gauge has to be installed in the cluster to show proper value - in this case there needs to be an additional resistor somewhere. This is where I need helping answer, unless I am doing something wrong that I am not aware of.

I did not measure resistance - from what I remember, for the new type of sender it is between 85 Ohm for full and 4 Ohm for empty. I can check it, but I do  not think this would be an issue...
Pawel

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lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #6 on: November 07, 2020, 16:49:39 »
Ok did some research and read some interesting post on these same issue like:

https://www.sl113.org/forums/index.php?topic=4153.0

Apparently for MB W113 250Sl and 280sl the resistance readings at the fuel gauge are as stated on my previous post.

Full = very low resistance close to 5 ohm
1/2 tank is about 100 ohm
1/4 close to 180 ohm.

To check this issue on your particular car you have to do as mentioned on ejboyd5 today.

So my work around would be to run a new ground line between fuel sender unit post where cable BLUE/black is attached and put in that same line a potentiometer in the range 0-200 ohm.  This ground line will run between fuel sender unit to instrument cluster fuel gauge connection at the 12 pin connector below the steering wheel (cable BLUE/BLACK) The objective of this line will be to drop the total resistance read by the fuel gauge by having a resistance controlable line. 

1. So you take out your fuel sending unit and move the float to the full position.   
2. You observe the behavior of your fuel gauge, which I will assume is not marking full as desired.
3. The separated ground line with inline potentiometer installed in the range 0 to 200 ohm will allow us to compensate all the voltage loses on the original circuitry.
4. We place first the potentiometer at the maximum resistance position.
5. We reduce gradually the resistance on the parallel ground line by means of turning the knob on the potentiometer in the direction to which it gives the lower resistance value.
6. We keep turning slowly it and as soon as our fuel gauge indicates fuel there is the sweet point.

We test again in that set value moving the float to the 1/2 level position and see again how our gauge behaves.  Make the necessary adjustments on the potentiometer to have the most accurate measurement possible.

Enjoy your experiment.

lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #7 on: November 07, 2020, 16:59:43 »
Dear Pawel

I think that your problem and mine, because it has happened to me also on one of my mercedes is that fuel gauge never marks full.  So there is much resistance in the path of electricity from the tank fuel sender to the fuel gauge.

In order to fix this we need to find a way to make the gauge read lower resistance values.

One way to check if our gauge is OK will be first to take the gauge out (the full instrument cluster) one on a bench see how it behaves connecting its feed wires directly to a 12v dc source.  The cables are these

12v (+) source is BLACK/blue stripe
12v (-) is BLUE/black stripe.

If we connect the gauge directly to a battery 12.6 volts it should mark FULL.

THEN we on the negative side install a cable with and embedded potentiometer (that is like a volume adjusting knob) in the range 0 to 200 ohm.

We move the knob and see how the gauge moves.

In theory with very low resistance values, let’s say 5 ohm, gauge should mark FULL.

With 100 ohm should mark 1/2 tank and with 180 ohm 1/4 or less.

Let’s do the experiment and then decide how to solve the puzzle.

Best regards
L.peterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #8 on: November 07, 2020, 17:08:30 »
Ok did some research and read some interesting post on these same issue like:

https://www.sl113.org/forums/index.php?topic=4153.0

Apparently for MB W113 250Sl and 280sl the resistance readings at the fuel gauge are as stated on my previous post.

Full = very low resistance close to 5 ohm
1/2 tank is about 100 ohm
1/4 close to 180 ohm.

To check this issue on your particular car you have to do as mentioned on ejboyd5 today.

So my work around would be to run a new ground line between fuel sender unit post where cable BLUE/black is attached and put in that same line a potentiometer in the range 0-200 ohm.  This ground line will run between fuel sender unit to instrument cluster fuel gauge connection at the 12 pin connector below the steering wheel (cable BLUE/BLACK) The objective of this line will be to drop the total resistance read by the fuel gauge by having a resistance controlable line. 

1. So you take out your fuel sending unit and move the float to the full position.   
2. You observe the behavior of your fuel gauge, which I will assume is not marking full as desired.
3. The separated ground line with inline potentiometer installed in the range 0 to 200 ohm will allow us to compensate all the voltage loses on the original circuitry.
4. We place first the potentiometer at the maximum resistance position.
5. We reduce gradually the resistance on the parallel ground line by means of turning the knob on the potentiometer in the direction to which it gives the lower resistance value.
6. We keep turning slowly it and as soon as our fuel gauge indicates fuel there is the sweet point.

We test again in that set value moving the float to the 1/2 level position and see again how our gauge behaves.  Make the necessary adjustments on the potentiometer to have the most accurate measurement possible.

Enjoy your experiment.

Thank you!

But I am afraid this is not the issue I am chasing now... :)

I saw this post when I was searching the Forum earlier.

I have the Ohm values, thank you, 5, 100, 180 - I can do the check.

I can also check if there is "unwanted" resistance somewhere in the car, simply by measuring it at the pin on the handshake connector.

My question remains: is there an additional resistor in the instrument cluster for fuel gauge? Or the one on the wiring diagram is the one inside the gauge. In other words - can I test the gauge just by connecitng it to the sender in the trunk?
Pawel

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lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #9 on: November 07, 2020, 17:15:48 »
You can test directly to the fuel sender but you will loose the resistance caused by electricity path trough the long wiring harness.  Is not so neglectable since wire gauge is very very thin.

By doing this test directly you will have higher gauge readings since resistance has dropped.

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Re: Fuel Gauge Connected Directly To Sender
« Reply #10 on: November 07, 2020, 17:19:09 »
Ok did some research and read some interesting post on these same issue like:

https://www.sl113.org/forums/index.php?topic=4153.0

Apparently for MB W113 250Sl and 280sl the resistance readings at the fuel gauge are as stated on my previous post.

Full = very low resistance close to 5 ohm
1/2 tank is about 100 ohm
1/4 close to 180 ohm.

To check this issue on your particular car you have to do as mentioned on ejboyd5 today.

So my work around would be to run a new ground line between fuel sender unit post where cable BLUE/black is attached and put in that same line a potentiometer in the range 0-200 ohm.  This ground line will run between fuel sender unit to instrument cluster fuel gauge connection at the 12 pin connector below the steering wheel (cable BLUE/BLACK) The objective of this line will be to drop the total resistance read by the fuel gauge by having a resistance controlable line. 

1. So you take out your fuel sending unit and move the float to the full position.   
2. You observe the behavior of your fuel gauge, which I will assume is not marking full as desired.
3. The separated ground line with inline potentiometer installed in the range 0 to 200 ohm will allow us to compensate all the voltage loses on the original circuitry.
4. We place first the potentiometer at the maximum resistance position.
5. We reduce gradually the resistance on the parallel ground line by means of turning the knob on the potentiometer in the direction to which it gives the lower resistance value.
6. We keep turning slowly it and as soon as our fuel gauge indicates fuel there is the sweet point.

We test again in that set value moving the float to the 1/2 level position and see again how our gauge behaves.  Make the necessary adjustments on the potentiometer to have the most accurate measurement possible.

Enjoy your experiment.

Yes, the potentiometer would then act as the fuel sender.

Since I do not have any potentiometer at hand, I will check what resistance fuel sender has now. I may also have a handful of resistors, I would need to check their resistance, but I am afraid they are higher value.

Regardless of that: when I connect the gauge that I have from the box form SLS - it reads full whenhooked on the bench (in the trunk) with sender in series between ground and this gauge.

Again, unless there is a resistor in the instrument cluster in that circuit, I think this new gauge is broken.

What you are saying is suggesting there is no such resistor in the instrument cluster and the one showed on wiring diagram is the one inside the gauge.
Pawel

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Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #11 on: November 07, 2020, 17:27:58 »
You can test directly to the fuel sender but you will loose the resistance caused by electricity path trough the long wiring harness.  Is not so neglectable since wire gauge is very very thin.

By doing this test directly you will have higher gauge readings since resistance has dropped.

Aha! So you are saying the resistance of the wiring between trunk and instrument cluster is not neglectable? if I have roughly 1/3 or 1/4 of fuel in the tank, the sender resistance should be, say 130 Ohm - that is what is already there. Gauge is reading full. So it is either wrong or it is missing this, say, 125 Ohms. There would have to be 125 Ohm in the wiring - does this make sense? So much? Unless there is some additional resistor there...
Pawel

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Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #12 on: November 07, 2020, 17:41:53 »
Let me show perhaps what I am looking for - please take a look at the picture.

Are there two resistors - one in the gauge, one in the instrument cluster?

Or the resistor on the diagram is the one in the gauge?
Pawel

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lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #13 on: November 07, 2020, 18:05:25 »
The resistor on the gauge is the one reflected by the diagram.

So it seems to me that there are to possible solutions......

Remove the resistor on the gauge itself and have there a variable adjustable resistance (potentiometer), or as you say when you connect the gauge directly to fuel sender readings are correct..... so that means that resistance on the wiring is important and is causing the error on the gauge reading.

So a solution  is to run a separated line to run in parallel with actual cable blue/black and have a variable resistance there. The parallel cable should be of a wider cross section let’s say 1.5 mm2 which equals to AWG16.  Remember cable blue/black is 0.75mm2

Un so weiter.....

« Last Edit: November 07, 2020, 18:23:10 by lpeterssen »

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Re: Fuel Gauge Connected Directly To Sender
« Reply #14 on: November 07, 2020, 18:16:04 »
Dear Pawel

You said:


I bought W113 late gauge form SLS. Before diving under dash I wanted to check it. I hooked + from fuse box, signal form corresponding pin in the sender and left ground connected to the sender from the harness (brown wire). The tank is 1/3 full. But the hand pegs at 4/4. I see 2 possibilities:
1. Something is wrong with the gauge.”

The ground side of the fuel gauge sender should be connected to BLUE/black that is the ground coming from the fuel sender float.

If you connect the fuel gauge directly to BROWN GROUND, it will receive a full signal ground and that is why is showing 4/4 full instead of 1/3.

The fuel gauge gets full 12v on the positive post (+)from cable BLACK/blue, and the negative signal is taken from the BLUE/black stripe cable coming from float (fuel sender unit)

lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #15 on: November 07, 2020, 18:21:56 »
Correction on my previous post.

The resistance indicated on your photo on the fuel gauge is ACCORDING to electrical diagram on the POSITIVE SIDE OF THE GAUGE on the black/blue stripe wire.  Is not on the negative side of the gauge coming from the sender.  This makes me conclude that fuel sender needs less than 12v to operate.

So all the comments related to running a separated negative with a variable resistor (potentiometer in range 0-200 ohm) line in parallel to Blue/black stripe cable coming from fuel sender can be maintained.


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Re: Fuel Gauge Connected Directly To Sender
« Reply #16 on: November 07, 2020, 18:53:41 »
Dear Pawel

You said:


I bought W113 late gauge form SLS. Before diving under dash I wanted to check it. I hooked + from fuse box, signal form corresponding pin in the sender and left ground connected to the sender from the harness (brown wire). The tank is 1/3 full. But the hand pegs at 4/4. I see 2 possibilities:
1. Something is wrong with the gauge.”

The ground side of the fuel gauge sender should be connected to BLUE/black that is the ground coming from the fuel sender float.

If you connect the fuel gauge directly to BROWN GROUND, it will receive a full signal ground and that is why is showing 4/4 full instead of 1/3.

The fuel gauge gets full 12v on the positive post (+)from cable BLACK/blue, and the negative signal is taken from the BLUE/black stripe cable coming from float (fuel sender unit)

I think I had it correct:

1. I took the gauge out of the box and took it to the trunk. It had two terminals:
- positive, goes through the resistor to the solenoid inside the gauge
- signal, goes directly to solenoid inside the gauge

2. I removed the plug from sender and wires from the plug; put blue/green (reserve light) and blue/black (signal to gauge in cluster) aside

3. Connected brown (ground) to its pin on sender

4. Took a length of wire and connected signal pin from sender to signal terminal in the gauge (so this is through resistance wire in the sender)

5. Took a length of wire and connected + from fuse box to positive terminal in the gauge

6. (Modified 12.12.2020) Gauge frame was grounded.

The gauge showed full despite 1/3 of fuel in the tank.

I did not connect ground to gauge - I did to pin on sender, then from another pin on sender I took the signal to the gauge.

If there is no other resistor in the cluster and if the resistance between brown and black/blue pins on sender is around 80-90 Ohm, this means the new gauge is shot.

Am I correct?

P.S. I have replaced the attached drawing with the corrected one - with ground for gauge marked (12.12.2020).
« Last Edit: December 12, 2020, 13:57:32 by Pawel66 »
Pawel

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lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #17 on: November 07, 2020, 22:05:11 »
Pawel you are right on the connections shown on the scheme.   Either your sender unit is not giving the right resistance values to the gauge or the gauge is shot as you say.

There is still one experiment to do.

Work only with the gauge to find out which resistance values make it work correctly.  Work on a bench, have a tester on hand which can measure resistance, and have a potentiometer to allow you to change resistance values.

Remember that one of the post mentioned on this forum topic said that correct values were:

Full tank = resistance close to zero, around 5 ohm
Medium tank= resistance around 100 ohm
Empty = around 180 ohm.

Enjoy your test and share the conclusions with us.

 Event regards
Lpeterssen
« Last Edit: November 07, 2020, 22:11:28 by lpeterssen »

Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #18 on: November 07, 2020, 22:23:10 »
Yes, before I read your post, I undertook some actions!

I bought potentiometer 200Ohm. I also bought a handful of resistors 10, 20, 50, 100 and 150 Ohms.

Maybe I can calibrate this thing to work. I will do it on the bench before removing/checking the sender. It is potentially about increasing resistance, maybe it will work.

Thank you for your patience, again, and kind attention!
Pawel

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Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #19 on: November 08, 2020, 00:52:12 »
Now I am thinking about the gauge I have in the car currently.

It shows roughly 1/4 less than actual. Resistance is too high by 25%.

Say: for empty it gets 180 Ohm instead of 135. So: what parallel resistor should I add between ground and signal pins to get it to 135 Ohms?

If 1/R1+1/R2 = 1/Rt (where Rt is total resistance of the parallel resistors), we would have:

1/180 + 1/Rx = 1/135

Rx = 1kOhm roughly

For half full:

1/100 + 1/1000 = 1/Rt

Rt = 91 Ohm

For full

1/5 + 1/1000 = 1/Rt

Rt = 5

Does this make any sense? I do not think so. The parallel resistor would have to be variable. For the full tank it becomes negligible, the result is still 5 Ohms that do not work... it would help when empty, half helped with half of tank, no help when full. Would show you true level when close to empty.

If you start form full:

1/5 + 1/x = 1/3.75

x = 15 Ohm

For empty:

1/180 + 1/15 = 1/Rt

Rt = 14 Ohm

Nonsense...
Pawel

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scoot

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Re: Fuel Gauge Connected Directly To Sender
« Reply #20 on: November 08, 2020, 03:36:47 »
I assume you have tested and eliminated the fuel sender as the problem.  If not, if you have an Ohm meter, here's a little diagram I made many years ago when I was cleaning and selling fuel senders....
Scott Allen
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Altadena, California

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Re: Fuel Gauge Connected Directly To Sender
« Reply #21 on: November 08, 2020, 09:03:54 »
Hi,
my 2 cents of knowledge:
- fuel sender and fuel gauge must fit together otherwise fuel showing is wrong
- fuel sender sends resistor values to the gauge depending on a floater and definite resistor wires in the tube
https://www.sl113.org/forums/index.php?topic=31224.msg226551#msg226551
- resistor at the fuel gauge reduces motion of the needle (attenuation)
...WRe

Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #22 on: November 08, 2020, 09:45:30 »
Thank you for inputs!

Scoot, the values, e.g. .069 are Ohms?

I thought it was ca 5Ohms in up position and ca 180 Ohms i n down position?
Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #23 on: November 08, 2020, 11:12:19 »
Hi,
did you recognize the VDO specs?
...WRe

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Re: Fuel Gauge Connected Directly To Sender
« Reply #24 on: November 08, 2020, 11:29:42 »
Dear Pawel

Repeated your math with a different approach a came to the same conclusion, we need to reduce resistance on the parallel line by 1000 ohm.  So negative resistance.

So I think that best approach is to make actual reading on the field and see which values are getting to the fuel gauge from the fuel sender.  This air assumptions of values is bringing us nowhere.

We need to establish first which resistance values make the fuel gauge you have on hands mark full tank, half tank and empty tank.

Then we need to read which resistance values are the output of your actual fuel sender in the same three positions full tank, medium tank and empty.  From that real data we can start and think if there is a feasible solution or not.

Best regards
L.peterssen
« Last Edit: November 08, 2020, 11:42:52 by lpeterssen »

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Re: Fuel Gauge Connected Directly To Sender
« Reply #25 on: November 08, 2020, 12:41:20 »
See idea.....

scoot

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Re: Fuel Gauge Connected Directly To Sender
« Reply #26 on: November 08, 2020, 14:49:21 »
Thank you for inputs!

Scoot, the values, e.g. .069 are Ohms?

I thought it was ca 5Ohms in up position and ca 180 Ohms i n down position?
I probably mean 69 Ohms and 6 Ohms.  I don't remember what the knob was set at when I did this.  It was 10+ years ago...
Scott Allen
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Altadena, California

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Re: Fuel Gauge Connected Directly To Sender
« Reply #27 on: November 08, 2020, 14:52:19 »
See idea.....

Brilliant! This is an adjustable amperage booster. I will check it out!
Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #28 on: November 08, 2020, 14:52:50 »
I probably mean 69 Ohms and 6 Ohms.  I don't remember what the knob was set at when I did this.  It was 10+ years ago...

Yes, most likely, thank you!
Pawel

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Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #29 on: November 08, 2020, 14:54:28 »
Hi,
did you recognize the VDO specs?
...WRe

This is great! Do we know which one is for the Pagoda?

If anybody has one out, we could check the length...
Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #30 on: November 08, 2020, 15:27:41 »
Hi,
as far as I can remember this could be the right one.
...WRe

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Re: Fuel Gauge Connected Directly To Sender
« Reply #31 on: November 08, 2020, 17:54:53 »
Did some checks. Internet stores are great in finding the part numbers.

MB number A 110 542 12 04 is a VDO number  VDO 224-817-001-014R indeed, WRe is absolutely correct.

So the numbers are 5 for full to 66 Ohm for empty.

I found some resistors in a drawer I would prefer to forget and quickly bench tested the gauge.

20 Ohm reading 4/4
50 Ohm reading 4/4
130Ohm reading 4/4
200 Ohm moves 1 mm above zero...

I will do the test with potentiometer, but I think the new gauge from SLS is shot (now when I know there is no additional resistor in the instrument cluster). Wonder what SLS will say. Or, actually, not wondering, I think I know what they will say...
« Last Edit: November 08, 2020, 18:00:05 by Pawel66 »
Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #32 on: November 10, 2020, 08:28:09 »
Hi,
my 2 cents of knowledge:
- fuel sender and fuel gauge must fit together otherwise fuel showing is wrong
- fuel sender sends resistor values to the gauge depending on a floater and definite resistor wires in the tube
https://www.sl113.org/forums/index.php?topic=31224.msg226551#msg226551
- resistor at the fuel gauge reduces motion of the needle (attenuation)
...WRe

Hi,
I thought again about the resistance in the fuel gauge and came to the conclusion that it does not contribute to the attenuation, but to an accurate value/adjustment between sender and display. In my opinion, the tube in which the floater swims and the narrowed inflow contribute to calming the needle in contrast to the old open floater.
...WRe

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Re: Fuel Gauge Connected Directly To Sender
« Reply #33 on: November 11, 2020, 12:08:24 »
Dear Wre

I do not think so....  I once did the following with a VDO temperature gauge (electric of course) which was NOS but for Mercedes trucks, therefore was designed to work in 24V. That gauge came with a large resistance on the positive side. As you know the negative side goes to a bimetallic probe which sends the negative signal which varies its value in the same way temperature does.

Well the case was to make it work on a MB w113, since it had exactly the same temperature range and vertical configuration. So we decided just to change that resistance from its original value to another which was exactly 1/2 (24V to 12v) and it worked fine up today.

So what I think is..... that electric gauges made by VDO of that era are adapted with that resistance to work either with 12v cars or 24V cars....

Best regards
L.peterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #34 on: November 13, 2020, 20:13:02 »
I checked again with potentiometer - I think the gauge is shot.

With 6-66 Ohm imitated sender resistance it pegs 4/4. When I hooked additional 250Ohm in series, within 6-66 Ohm sender resistance the gauge hand moves between 4/4 and 3/4.

I am sending it back.
Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #35 on: November 15, 2020, 11:09:18 »
Yes it seems so to me also.

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Re: Fuel Gauge Connected Directly To Sender
« Reply #36 on: December 12, 2020, 13:54:47 »
The SLS behaved very professionally and sent a new gauge to me. This one works as it should on the bench. I will replace it.

I am enclosing amended drawing for testing gauge on the bench before installation. In the previous one ground for the gauge was not marked. It is important, because you cannot see it clearly on the wiring diagram of the car.

Which connector is which in the gauge - you need to look and figure out (straight to coil, one with resistor, one grounded).

If you experience the hand not moving freely, it is a question of loosening a bit one of the screws that hold coil/hand assembly to gauge frame.
Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #37 on: December 12, 2020, 21:53:22 »
Excellent Pawel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #38 on: April 11, 2023, 17:28:27 »
I assume you have tested and eliminated the fuel sender as the problem.  If not, if you have an Ohm meter, here's a little diagram I made many years ago when I was cleaning and selling fuel senders....

Hiya Scott
Just looking at my sender unit now, bit annoyed as was only replaced a year ago so checking if it is the problem. From the great little diagram you created (which incidentally I think should be in the tech manual), are the ‘results’ in ohms? Also are the ‘pins’ the same for the early sender (with arm outside) as the latter (mine is the early variant)

Thank you!
Katie
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #39 on: April 12, 2023, 09:57:54 »
Hello Katie, i don't know the pin numbers, but as far as i understand, if you measure between the earth pin (connected to the brown wire)

Earth to the pin connected to the blue/green wire, should read 0 ohms when the arm is at the lowest position
Earth to the pin connected to the blue/black wire, should read between 6 ohms and 66 ohms (according to other posts) depending on the position of the arm

Also worth checking you have a good earth on the brown wire pin, i think the earth is connected somewhere in the boot, just need to trace the wiring loom
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Re: Fuel Gauge Connected Directly To Sender
« Reply #40 on: April 12, 2023, 12:49:36 »
Thank you!  :)
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #41 on: April 14, 2023, 13:58:10 »
Hi folks.
So, could someone advise how I take the sender out please?
I’ve taken the nuts and washers off and I thought would just pull off. I seems to be rather stuck! Any tricks of the trade on how to remove? It was recently replaced so I wouldn’t think corrosion was the issue?

I know the tank should be pretty full, to did do a quick test across the ground and the pin above. Showed as zero so presume that an indicator of the sender unit being faulty, looking at previous comments?
Ta
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Re: Fuel Gauge Connected Directly To Sender
« Reply #42 on: April 14, 2023, 14:41:55 »
Use a long handle flat screwdriver, stick it under the lip of the sending unit and work it around in a circle to break it free and it will lift right out.

Or you can use 2 flat screwdrivers and wiggle side to side.
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Re: Fuel Gauge Connected Directly To Sender
« Reply #43 on: April 14, 2023, 14:42:26 »
Hello Katie, before you try removing it, just to check that you're measuring between the pin that connects to earth, not actual earth, as there won't be an earth connection present when the plug is disconnected

If you're sure the sender may be at fault i understand that you just need to gently persuade it to release by moving it from side to side and perhaps pull up very gently by pins.  It should only be the studs and gasket holing it in place, although they may have added some sealant as well if it's been replaced

Be careful as the tube will be full of fuel when you pull it out, probably best done with the battery disconnected - that was a stupid thing to say, your sender doesn't have a tube!!!
« Last Edit: April 14, 2023, 14:48:12 by BobH »
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Re: Fuel Gauge Connected Directly To Sender
« Reply #44 on: April 14, 2023, 14:59:25 »
Just had a look at the pin configuration again, it looks like measuring between the earth pin and pin next to it should give you the variable resistance, depending on the position of the arm

The earth pin and the pin above it should be open circuit when the tank is more than a quarter full, dropping to zero ohms when the fuel is low, i think this is the low fuel lamp feed
« Last Edit: April 14, 2023, 15:13:05 by BobH »
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Re: Fuel Gauge Connected Directly To Sender
« Reply #45 on: April 15, 2023, 10:26:19 »
Hi everyone
The mystery continues.
So reset resister reading to 2k(?!?!) and now have a reading of 0.011ohms. So perhaps working or stuck?
I have looked everywhere but can’t find the earth. Could it be hidden under the silver (vibration / sound deadening) film? I also have a mysterious ‘hole’ towards the back of the boot/trunk to the left. Looks like not use for some time though. Any ideas what that was for?
Is there a way of checking if there is a good earth
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #46 on: April 15, 2023, 12:11:24 »
Ok, so got multimeter out again.
I’ve switched on the ignition, then placed  negative probe into earth, then positive into the other terminal.
This shows as 6.6v. So, to me, this shows that earth is ok?
Just trying to check alternatives before pulling out the sender which appears determined to remain in place!!
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #47 on: April 15, 2023, 12:18:32 »
Hello Katie, on the 2000 ohm scale, you're reading 11 ohms, so this may be ok, depending on the position of the sender float, better using the 200 ohm scale

To check the earth on the plug/connector, find an earth in the boot/trunk, there are earths next to the tail light bulb holders.  Hold one lead of the meter on the earth and the other lead on the brown wire in the plug, and you should read 0 ohms.  If it reads open circuit (OL) then you've lost the earth somewhere

I've read that the earth wire connects somewhere near the wheel arch, but i've looked in my car and i can't find it, the cable runs through the boot/trunk wall towards the soft top storage well, so maybe early cars were different.  It might be intrusive trying to trace it, so it may be easier to run a new earth wire, from the tail lamp earth connection to the earth connection on the plug.  If you run a temp wire, just hold it on the plug connection (with the plug fitted onto the sender), then the gauge should read

If the sender proves to be ok, and the earth is good, then there may be a problem at the instrument cluster plug or the gauge itself

Good luck
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Re: Fuel Gauge Connected Directly To Sender
« Reply #48 on: April 15, 2023, 20:50:34 »
Thanks Bob

Out will come the multimeter again!!

I think gauge is ok as when the plug is removed from the sender unit, fuel gauge goes straight to full. If the gauge not working, I presume the gauge wouldn’t move? The gauge has recently been refurbed, so certainly hope it’s not that!

Advice greatfully received
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #49 on: April 15, 2023, 21:17:57 »
That's not right Katie, the gauge gets it's earth (-ve) from the sender. With the plug removed there should be no earth at the gauge and it should read empty.  It sounds like its getting a full  earth, with no resistance, on pin d on the instrument cluster plug from somewhere else, perhaps the cable from the sender to the dash has got crushed shorting the brown wire to the blue/black wire.  Could that have happened recently?

I know it's a pain, but you need to pull the plug at the cluster and meter out the cable to the sender, to make sure there is no continuity, ie OL, between all cores when both ends are unplugged.  Probably easier to test at the plug in the boot.  If the wiring loom is original there is a chance that the insulation has failed and the wires are shorting out

What are the actual symptoms when the cable is plugged onto the sender and the ignition is on, what does the gauge read then?
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Re: Fuel Gauge Connected Directly To Sender
« Reply #50 on: April 16, 2023, 10:12:46 »
Hi Bob!
So when plugged in, the gauge showed some fuel, I filled the car up and no fuel showed!!
How dos one remove the cluster, is it a case of simply prising out, or are there some annoying screws behind dash holding this in place?
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #51 on: April 16, 2023, 11:25:15 »
I've never needed to remove mine, so i'm not sure, here's a picture of the connector, it may be obvious when you see it, whether there's a fixing screw or you just need to pull it apart.  Looks like the connector isn't actually fixed to the cluster, which may make it easier to access

https://www.sl113.org/wiki/Electrical/InstrumentCluster

Here's another picture

https://www.sl113.org/wiki/Electrical/Rheostat
« Last Edit: April 16, 2023, 11:36:47 by BobH »
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Re: Fuel Gauge Connected Directly To Sender
« Reply #52 on: April 16, 2023, 16:45:22 »
Be careful when navigating around the back of the center gauge cluster. The temperature gauge is a sealed unit and rather fragile. The oil gauge is a direct connection to the engine and can give you a nasty leak or worse.

It is not held in placel

Do a search and you should be able to find information about the removal.
Jonny B
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Re: Fuel Gauge Connected Directly To Sender
« Reply #53 on: April 16, 2023, 17:11:44 »
I don't think Katie needs to touch the cluster, which is fortunate, the connector is separate, mounted to the chassis somewhere under the dash
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Re: Fuel Gauge Connected Directly To Sender
« Reply #54 on: April 16, 2023, 21:13:26 »
I’m prepping myself to go in!!!😳

If you hear a lot of swearing from where you are, it’s probably me! 🤣
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #55 on: April 24, 2023, 21:42:46 »
Does anyone know why you cannot put in the ‘newer style’ fuel sender to replace the ‘float’ version?
I saw the answer somewhere but can’t find now!
Thank you
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #56 on: April 25, 2023, 23:07:07 »
I can’t answer your question fully — but I recall reading that the fuel sender is matched to the gauge -  the early senders only work with early gauge and later senders only work with later gauge.  I cannot confirm this first hand, just paraphrasing what I recall reading here. 

Also see JA17 response here:  https://www.sl113.org/forums/index.php?topic=17493.msg121156#msg121156

I bet one of our several knowledgeable techies will know ….
« Last Edit: April 25, 2023, 23:34:01 by kampala »
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Aslam

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Re: Fuel Gauge Connected Directly To Sender
« Reply #57 on: April 26, 2023, 07:35:38 »
I can’t answer your question fully — but I recall reading that the fuel sender is matched to the gauge -  the early senders only work with early gauge and later senders only work with later gauge.  I cannot confirm this first hand, just paraphrasing what I recall reading here. 

Also see JA17 response here:  https://www.sl113.org/forums/index.php?topic=17493.msg121156#msg121156

I bet one of our several knowledgeable techies will know ….

Thanks Aslam
Yes, I thought I read it somewhere as well? I wonder if it’s something to do with the resistor as I think the string mentions the gauge has a resistor in it and obviously the fuel sender unit has some sort of variable resistor in it?
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #58 on: April 26, 2023, 23:38:43 »
In my understanding THE RESISTOR which is installed ON THE POSITIVE side of the fuel gauge is intended only to adjust voltage being used by gauge coil that generates the magnetic field needed to move the indicator needle.

The same gauge coil is used on car/trucks running on 24v and 12v.

So, that resistance there, has nothing to do with the variable one that is on the fuel sender negative pole that feeds the other side of the gauge coil.

I have said many times that problem of Katies car is related to the quality of the wiring going to the fuel sender which is prone to internal oxidation. I have seen that many times in all the wiring harnesses I have rebuilt to mint condition so far.

The ground connection at the trunk left fender should be of optimal quality and that is overpassed all the time.

Second, the blue/green and blue/black cables get damaged due to oxidation. Those cables in many mercedes are from copper wires covered with a kind of aluminium alloy.  The fact is that when you sand them to make possible a new solder on the 4 pole connector at the sender, they break easily. Its better to replace them in full with new lines from the 12 pin connector at LHD footwell to the trunk without SPLICES.  Remember that a very low voltage passes through them.

Do not think that harnesses do not AGE. They do and those conductors made with materials that suffer from aging MUST BE REPLACED.

Not all the wires age the same
Way, depends on the kind of insulation used for the outer jacket, and kind of alloy of which the conductors are made.

Cables made of full copper tend to be in excellent shape after 50 years. Others made with different alloys get oxidized increasing the internal resistance, affecting therefore its performance.

Insulation jackets made of cotton/resin which by the time these cars were produced was the best material for heat shielding, has demonstrated that does not age well, and in many ocasions get’s brittle and disintegrates.

Best regards
L.Peterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #59 on: April 26, 2023, 23:52:14 »
A final way to discard if the fuel gauge is ok will be to connect it directly to the fuel sender

That can be done either by taking out the fuel sender out of car or by bringing the fuel
Gauge to the trunk and building a provisional wiring setup copying that section of the wiring diagram as shown on the technical section of this forum

That will be:

1. Find a 12v positive source. That will go on one end of the fuel gauge terminals
2. Find an excellent ground connection and feeding that to the fuel
Sender 31 terminal
3. Connecting a good quality wire in the position where the blue/black line is at fuel sender and bringing the other end to the still unconnected terminal at fuel gauge

Then move the fuel sender so that the inner float moves and observing the corresponding movement at the fuel gauge

Best regards
Lp

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Re: Fuel Gauge Connected Directly To Sender
« Reply #60 on: April 27, 2023, 08:09:43 »
Thanks LP

I’m sure the harness will need to be done at some point, but presently I have a girlie week away planned so that is not an option. Sounds like a ‘winter job’.

Apparently the more ‘modern’ sender has been installed, but I remember seeing somewhere that these are not interchangeable. Though it did work, to some extent, I had the the fuel gauge refurbed, the system then failed to work.

Logic would dictate, surely, that one or other (sender unit or fuel gauge) are no longer compatible?

Hence my follow up question as to why the two design of sender units are not compatible? 😁

Katie
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #61 on: April 27, 2023, 09:02:54 »
Hello Katie, there are several posts that confirm that the new style sender is not compatible with the early gauge, the resistance in the later senders is different from the early senders, so i assume the gauge must be calibrated accordingly, hence they need to match.  Perhaps this has been your problem all along, and your wiring may be ok?  No point checking the loom any further until you're confident that the sender and gauge are compatible
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Re: Fuel Gauge Connected Directly To Sender
« Reply #62 on: April 27, 2023, 14:59:18 »
Katie

There is always a workaround. Its just a matter of thinking.

The things that we need to know are:

1. Resistance values read at the new fuel sender with float at full position and at empty position
2. Connect the fuel gauge on one side to a pure 12v source
3. The other side of the fuel gauge at a negative source with AN INLINE POTENTIOMETER or variable resistance that will allow us to determine at which resistance value the gauge marks FULL and at which value the Gauge marks EMPTY.

You will read resistance values with a multimeter connected in parallel at the negative side

Once you have those values. Make a new post and notify me by direct message to THINK OVER A POSSIBLE SOLUTION to make those two actually incompatible devices to talk each other in the same language

Best regards
Lp

Sorry for fast typing but internet is terrible now here in my home address
« Last Edit: April 27, 2023, 15:07:05 by lpeterssen »

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Re: Fuel Gauge Connected Directly To Sender
« Reply #63 on: April 28, 2023, 18:25:22 »
That would be a really nice thing to have documented going forward as the older style senders will presumably get harder and harder to source.  Would be a nice product you could market.
Rodd

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Re: Fuel Gauge Connected Directly To Sender
« Reply #64 on: May 03, 2023, 11:53:43 »
Hi all, so all fixed after a bit of head scratching. So, sequence of events:

a) I complained that Bessy’s fuel gauge was bouncing all over the place, more so than others had discussed
b) the fuel sender unit was replaced, what I hadn’t realised at the time was that the newer design of sender unit had been installed. Weirdly this did work to some extent (be looking back neither me nor the garage can understand how it worked unless some odd thing was going on with the resistor in the fuel gauge).
c) still wasn’t too happy, although working, with the gauge and sporadic fuel levels. As speedo had to come out for a refurb, decided to have fuel gauge refurbed.
d) with refurb, Bessy obviously remembered that the new design of fuel sender unit and fuel gauge were not compatible, but didn’t decided this straight away as it did work for a short time! Typical lady, wanted some time to make a decision!?!?
e) testing then was made, as we know, fuel sender with float worked with refurb fuel gauge. New design fuel sender now not working!
f) garage concerned that if put the ‘float’ style sender in, liklihood fuel gauge would bounce around.
g) solution. Put a 280SL fuel gauge, which looks the same from driver’s view, into Bessy! So now have the more ‘modern’ set up which all seems to be working well 😁
230SL

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Re: Fuel Gauge Connected Directly To Sender
« Reply #65 on: May 03, 2023, 14:16:04 »
You must be very relieved!  I know you like to drive the car, so having a good working gauge is necessary.  Good job working through it to resolution.
Rodd

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Merc_Girl

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Re: Fuel Gauge Connected Directly To Sender
« Reply #66 on: May 03, 2023, 14:38:19 »
Thanks Rodd

Maybe helpful to others who have the early pagodas who wish for something a little more ‘helpful’ and not too ‘sensitive’ to latter ‘amendments’. 😁
230SL

lpeterssen

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Re: Fuel Gauge Connected Directly To Sender
« Reply #67 on: May 05, 2023, 10:14:04 »
Dear Katie

Happy  to hear that you came to a final solution with the 280SL later style fuel gauge.

Nevertheless I would like to have my hands on an early style fuel gauge and a modern style fuel sender to find a way to make them work together correctly.

If anyone is willing to send me theirs old style fuel gauge to my postal address in Miami, I am willing to solve the puzzle for all.

Best regards
L.Peterssen
Contact me to l.peterssen@me.com

acbrock

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Fuel Gage Not working
« Reply #68 on: July 30, 2023, 02:14:29 »
Hi, new to the forum.  I have searched and dont see any answers for this so if there are already posts.. Sorry!  I will learn to find stuff as I keep working my car.
I have a 1966 230SL.  I have had it for about 20 years.  It has sat that 7 or 8.  The fuel gage is not working.  It worked last time the car was up and running.  It is just in the empty position with no Reserve light on.
I have pulled some of the parts and it seems like power is good from the battery to the Plug on the Fuel sender.  Everything on the dashboard works except the fuel gage.
My next step was to remove the Fuel sending and see if there were any issues I could see.  I took the plug off and remove the 5 or 6 nuts but it won't come out.  I am assuming it is just sealed in there and I just have to dig under the black metal ring and try and release the seal and then slowly pull it out.   I just wanted to check if that I right before I start trying to pry it out, because I dont see any other connectors.

Is this the best next step?  Also since I am going no gage now.. how many approx miles should this car get?  If I fill the tank and zero out the Trip Distance.  I dont plan to push it to any limit but just curious if it was 200 miles?
Thanks
A

1966 230SL Automatic 717G Papyrus White "Minny"

acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #69 on: July 30, 2023, 02:19:29 »
OMG!  When I hit save and went to check my post all the information was right there above my post.  Not sure how I missed it.  My computer is acting funky still asking me to become a full member even though I have already paid.  I think I am just going clear everything and logout and back in and maybe my searches will be better...
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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #70 on: July 30, 2023, 02:35:41 »
So reading all this new information that popped up I saw someone state that the Gage when full when unplugged from the Fuel Sender.  So I tried that, and it stayed empty but now playing around and really watching, when I start the car or turn it on the gage jumps a tiny bin but when I unplug it from the Sender and turn it on it does not move.  So I am thinking maybe the actual gage is stuck?  Is there anyway for me to send the correct current thru the plug to the gage to see if I can make it move to full?   When I use my multi meter on the actual fuel sender I am getting no readings.  So I am going to maybe get a new multimeter or watch some videos in case I am using it in correctly.  I was putting on check function and was touching the leads to the 3 poles and was getting no readying at all.
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rwmastel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #71 on: July 30, 2023, 03:37:20 »
acbrock,

Welcome to the Group!

I'm not sure you're problem is in line with the rest of this thread.  Might have been better to start your own with an appropriate title.

If writing a really super long post, I sometimes do it in MS Word or something so I can take my time, walk away, come back, do some research, etc., then paste it in the forum.  This site can timeout your post if you're taking a long time.

I hope the Search feature gets more comfortable for you.  We've been online 20 years, so there's a lot you can lfind and learn on your own before even posting.

Good luck with your gage.
Rodd

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BobH

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Re: Fuel Gauge Connected Directly To Sender
« Reply #72 on: July 30, 2023, 08:30:11 »
Hello acbrock

I think most of what you need to know is in this post, you should also look in the tech manual for fuel gauge and the wiring diagrams for how the circuit works

There is a +ve on one side of the gauge and low fuel lamp, fed from fuse 5 when the ignition is on, so check that this is present.  You can test at the 12 way connector under the dash, the one that feeds the instrument cluster, so you don't need to remove the cluster or the gauge to test. 

A ground/earth is switched from the sender to the gauge the resistance varying dependent on the position of the float, and the ground is also sent to the low fuel lamp when the float is sitting low in the tank.  You should check for a good earth on the connector to the sender, the ground is picked up locally in the trunk/boot, so check for continuity between the ground and the earth pin on the connector, the plug details are on an earlier post on this thread or in the tech manual

There is no ground on the pins of the sender when the connector is unplugged, so don't test the sender itself, but you can test for resistance between the pins, which will prove if the coil of the sender is intact

There's quite a lot to digest, so carry out these steps first before you remove the sender from the tank

You can easily check your multimeter, just touch the two leads together when set to ohms and you should read 000, no resistance, and you can also check the battery voltage when set to DC volts to prove the meter

If you read OL when testing on ohms with the leads shorted, this indicates open circuit, there's a battery and a fuse inside the meter, so check both if it's not working correctly

Please let us know how you get on
February 1965 230SL Automatic
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Blue soft top
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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #73 on: July 30, 2023, 21:22:20 »
Hey Rod,
Yea my post did not seem to fit perfectly with the current question.  I was going to post a new question but I cannot find anywhere to Post a NEW Topic.  I could only find a way to reply.  The "Post" at the top of my window is not clickable?  I am wondering if that is because it is not recognising me as a full member?  Going to play around on other computers and browsers...

Bob thanks for the info! I am going to get into it today.  I will post what I find.

Thanks
Aaron
« Last Edit: July 30, 2023, 21:28:27 by acbrock »
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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #74 on: July 31, 2023, 02:16:37 »
Ok spent some time with the car today… Side note finally got the front right vent out.  That one was killing me.  I know just needed to force it but did not want to break anything.  So a little WD40 on the pins and finally pulled it out with out break a pin or the little hook clamp!  Wahooo!

But back to the Fuel Gage.  So before I pull the Fuel sending I did some MultiMeter tests.

I removed the Cap and connected the wires. 
With the Ignition OFF

Earth Connector to Earth on the rear light = 0
Earth to Blue/Black = 0
Earth to Blue/Green = 0
Blue/Green to Blue Black = 0

With Ignition ON

Earth to Blue/Black = 1
Earth to Blue/Green = 1
BG to BB = 1

With the Plug not connected to the Fuel Sender
Earth to Blue/Black = 0
Earth to Blue/Green = 1
BG to BB = 1

Does this make sense? If not let me know and I will do more research on my electrical skills.  I know little about a lot but not a lot about electrical things...
1966 230SL Automatic 717G Papyrus White "Minny"

BobH

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Re: Fuel Gauge Connected Directly To Sender
« Reply #75 on: July 31, 2023, 09:08:38 »
So reading all this new information that popped up I saw someone state that the Gage when full when unplugged from the Fuel Sender.  So I tried that, and it stayed empty...

Hello, don't get hung up on the above statement, it's not correct, with the sender connector plug unplugged the gauge will remain on empty, as there is no ground feed to it

i guess what you should try before anything else, is simply to tap the cluster glass with your finger, the needle can get stuck when the gauge hasn't moved for a while, my gauge needed a nudge for months until it eventually freed up through regular use

The next thing to try is to make sure you have a good ground at the sender unit, the brown wire on the connector, your readings in your last post may indicate that the ground is ok, but may not.  I suspect your meter may not have been used correctly, apologies if it sounds like i'm teaching you how to suck eggs

All tests should be carried out with the ignition off

With the meter set to ohms (omega sign) and the meter leads plugged into common and the terminal to the right, ohms, AmAv (terminal A to the left of common is not used for continuity tests).  Set the meter to 200ohms.  When the leads are shorted together, you should read 00.0

If that's ok, put one lead on a good ground, next to the rear lights is easiest, the other end of the lead on the brown wire on the connector, again should read 00.0.  If you read OL then run a temporary wire from the ground to the brown wire terminal on the connector and then try the gauge with the ignition on
February 1965 230SL Automatic
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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #76 on: July 31, 2023, 18:57:55 »
Bob, so I rechecked with the Meter.  Meter goes to 0.00 when I touch the leads and when I did the Ground from the Plug to the Ground at the rear light it goes to 0.00 too.   So assuming good ground.  I tapped the gage with no result.  Is there easy way to get at that gage or is it taking the whole dash apart.  I will start looking into that.  Everything works on the dash but the Odometer so I need to have that rebuilt or cleared up.

ps... no worries on sounding like you are teaching me!  I am here to learn!  Pretend I am 5 years old!  I guess I am not even 5 considering the years and experience I have working on cars!
« Last Edit: July 31, 2023, 19:34:32 by acbrock »
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rwmastel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #77 on: July 31, 2023, 19:31:54 »
Is there easy way to get at that gage or is it taking the whole dash apart.  I will start looking into that.
Getting the gages out is a bit of a pain, from what everyone says.  I've avoided it so far, but may be doing it this fall. 

Did you get the sender out of the tank yet?  Maybe the float is stuck.  If you do pull it out, buy a new seal for putting it back together.
Rodd

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BobH

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Re: Fuel Gauge Connected Directly To Sender
« Reply #78 on: July 31, 2023, 19:35:11 »
Before you start taking the gauge out, which entails taking the instrument cluster out, which is quite a task, you could just try eliminating the sender as the problem, by bridging the earth pin on the plug to the other two pins, ground to the blue black wire should activate the gauge, and ground to blue green wire should illuminate the low fuel light, do these tests with the ignition on

If both of those work, then the problem would seem to be with the sender, which could be damaged or could just need a clean, there's tips on how to pull the sender out on one of the earlier threads.  I'm not sure what condition your fuel and tank is in if it's been standing for years, i guess the tank may need emptying and flushing, if you search, again you'll get some advice

If linking across the pins still doesn't work, then you'll need to look at the actual wiring between the sender and the gauge, which goes via a 12 way connector under the dash, there's a picture of the pin arrangement in the tech manual, button above left, and then use the search function when you're on the tech manual home page.  You can visually inspect the connections at both ends, as the wiring can deteriorate over time, particularly where they are soldered onto the connector pins

You could also make sure fuse 5 is ok, i think that also serves the reversing lights and brake lights, so perhaps check if both of those are still working.  Sometimes the fuses need twisting in their holders, as they can build up resistance over time
« Last Edit: July 31, 2023, 19:59:31 by BobH »
February 1965 230SL Automatic
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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #79 on: July 31, 2023, 20:28:10 »
Awesome!  Thanks BOB!  That was the little trick I needed.   So when connecting wires, Reserve light went on and also Tank when full.   So I guess today I get that fuel sending out and hopefully just give it a good cleaning!
Thanks!
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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #80 on: July 31, 2023, 21:30:38 »
Always something.  So I got the sender out.  Figured I should take it apart and clean it.   Bottom metal piece came off I cannot get the plastic piece beneath it off. I feel like I am going to destroy it.  From the picture on the link below it looks like the plastic piece is just placed on there... Think I could just push the protruding screwpin from the bottom to pop the top of the sender off?  Or will I wreck the inside.  I might just put it back in now that I took it out and can hear everything floating around inside.  Maybe it just needed to be moved and drained?  Or think should soak it in water/venegar if I cannot get it open?

https://w113-eu.translate.goog/geschlossen/Reparaturen/Geber%20fuer%20Kraftstoffanzeige%20Pagode%20W113.htm?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp

Also just went out and attached the Sender to the car and turned it on and tilted it upside down and right side up.  Same problem I have had the whole time.  Nothing on the gage just a little jump.  So I am guess something is broken inside this sender?

After thinking about it... I guess if the Sender is bad then I should not worry too much about busting it open.  Kind of want to do it just to confirm it is broken inside... I searched and Mercedes has a parts shop near me and they have a new Fuel Sender I can pickup tomorrow for $200.  I might do that tomorrow or the next day.  Much cheaper than taking to the mechanic....
« Last Edit: August 01, 2023, 05:33:00 by acbrock »
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rwmastel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #81 on: August 01, 2023, 06:24:21 »
I think people have tried to clean these before, but maybe just chemically and not through disassembly?  This would have been a very good topic to search on, before taking it apart.  Some people like to make existing parts work, some like to replace everything with new.  Hopefully it can be salvaged.

You may need a professional fuel tank cleaning & sealing if it is rusty inside.  Some members attempt it themselves.

Replace the inexpensive fuel screen that is screwed into the bottom of the tank.

Replace the main fuel filter in the engine bay.

And which car (year) do you have?  It would be a good idea to put that in a signature so people can provide accurate help based on your car specifics.
Rodd

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BobH

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Re: Fuel Gauge Connected Directly To Sender
« Reply #82 on: August 01, 2023, 07:39:37 »
Have a search to find the best method of cleaning, you may be able to salvage it

You should always disconnect the battery when removing the sender, don't want any sparks when the tank is open and there are fumes in the trunk and car

Did you find out how to start a new post?  If you search the help pages, above left it will give you advice on how to navigate around the site

Good luck!
February 1965 230SL Automatic
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Pawel66

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Re: Fuel Gauge Connected Directly To Sender
« Reply #83 on: August 01, 2023, 09:11:13 »
If I may add, as I went through pulling out the sender:
- avoid doing that with completely full tank; with a full tank a small pressure on trunk floor may result in huge spillage of fuel through the hole where sender was
- get equipped with a new seal for sender before you start disassembly; best from Mercedes in my opinion
- be careful not to break off the studs from fuel tank; maybe apply some penetrant in advance on the nuts
- it is work with fuel - have something at hand (fire extinguisher, blanket) to put out fire
- avoid 220V portable garage lights
- as advised, disconnect battery
Pawel

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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #84 on: August 01, 2023, 16:23:11 »
Hey Gang thanks for all the input....

RW… I wills search the chemical cleaning now.  I never got it apart for fear of breaking it!  I am someone who will 100% always want to repair not replace.  I will check on the tank.  About a month ago when I decided to get it running again and start to restore, I took it into a shop that I had taken it in the past.   Actually the shop that has been servicing the car since 1971.  Unfortunately the shop changed hands about 3 years ago.  But one of the mechanics stayed on and he worked on the car.  So he went thru the car and drained the tank and replaced a bunch stuff so that I could feel the car was mechanically safe for me to drive.  So I will double check on what they found in the tank.  They were very impressed that the car had no rust, so I assume the tank should be ok.

BobH… Just so you dont think I am crazy.  Yes I had the battery off during all of this.  I only plugged it back in when I did the test on the Sender.  I covered the tank up and I am working outside.  But always feel free to send safety stuff, I know there are tons of little things that I might not realize are completely dangerous.  If I had not read about taking the battery off when working on the sender before I started I probably would not have thought it was necessary!

No still cannot post a new topic!  Can you send me a picture of the buttons you have?  Maybe I am starting right at it but in the help notes it says there should be a Post New at the top and Bottom and I dont have either?

Paw… Blew that, did not realize I had a full tank because I had no gage!  Or not full but full enough to make a mess!  I think I will go to Mercedes today and get the Sender and seal while trying to clean out the old one.  I got it off without hurting the studs!  Buying another fire extinguisher today!
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rwmastel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #85 on: August 01, 2023, 17:05:11 »
No still cannot post a new topic!  Can you send me a picture of the buttons you have?  Maybe I am starting right at it but in the help notes it says there should be a Post New at the top and Bottom and I dont have either?
Rodd

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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #86 on: August 01, 2023, 17:24:37 »
Yep it is there!  I guess it is just not on all the pages.  I only have it on the page when I back up to Electrical an Instruments.  It is not on this or the main Page.  So I guess I just need to find the correct group in the forum and post there.  Makes sense!  Knew it was something stupid and simple.
Thanks!
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rwmastel

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Re: Fuel Gauge Connected Directly To Sender
« Reply #87 on: August 01, 2023, 17:30:32 »
Well, you can't start a new topic from within a current topic, only from within the forum, if that makes sense?  So, if there is a list of topics displayed, then you can start an additional topic there.  Once you start discussing a few different topics and using the different sections of the forums, then it will all become second nature.

Getting used to the Search function is the most important thing!  Sooooo much information available.  You'll be a Pagoda Expert by Thanksgiving.   :D
Rodd

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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #88 on: August 02, 2023, 00:20:13 »
Ok now I can create new post!  I posted something earlier and added pictures but it is not here so maybe I dont have picture ability yet.   But went down to Mercedes Benz today in Long Beach what an insane facility.  They were working on a bunch of cars for the Pebble Beach show next month! Wow. So I bought a new Sender in case the cleaning Rehab on mine failed...

Search forum for Cleaning and sent a message to a guy who had done it a bunch of times.  Got my sender open to clean tons of crud came falling out.  I will attach a pic!  Then once I got the send out, 1 of the wires was not connected out of the 3.  And it was a mess.  I sent the pics off to the guy and he said it was the worst one he has seen and he would not tackle it.  So I did a quick clean and boxed it up to attack later in life when I get better at this.  Dropped in the New Sender and Boom!  Everything fired up and gage works perfectly!  So I think my probably (first of many) is solved so I won't post here anymore.  I will start new threads!  But I am sure I will track you all down with questions. 
So thanks for everything!
I am going to post his and see if it posts, then post the pictures in a separate post to see if they post...
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acbrock

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Re: Fuel Gauge Connected Directly To Sender
« Reply #89 on: August 02, 2023, 00:28:10 »
Pics...
1966 230SL Automatic 717G Papyrus White "Minny"