Fuel Gauge Connected Directly To Sender

[lpeterssen]

See idea.....

[scoot]

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...

[Pawel66]

See idea.....

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

[Pawel66]

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!

[Pawel66]

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...

[WRe]

Hi,
as far as I can remember this could be the right one.
...WRe

[Pawel66]

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...

[WRe]

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

[lpeterssen]

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

[Pawel66]

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.

[lpeterssen]

Yes it seems so to me also.

[Pawel66]

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.

[lpeterssen]

Excellent Pawel

[Merc_Girl]

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

[BobH]

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

[Merc_Girl]

Thank you! 

[Merc_Girl]

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

[Vander]

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.

[BobH]

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!!!

[BobH]

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

[Merc_Girl]

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

[Merc_Girl]

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!!

[BobH]

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

[Merc_Girl]

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

[BobH]

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?