Fuel Injection Pump Problems

[ja17]

Just disconnect the metal fuel line going to  the intake starting valve and temporarily clamp the fuel gauge on there.

[garymand]

From previous reply: "The cold start valve is a good place to do the measurements.  It is in the manual.  Ensure you are getting the required fuel pressure and volume to the FI pump.  Let us know."

[jackhughes81]

Is the Cold Starting Valve the same as the intake starting valve?  I am not familiar with the different names used for the same item, but I will learn thanks--  jack

In the technical manual it references a repair manual, which I do not have.  Is there a way to get a copy of this manual?  I find a lot of things in the technical manual online here reference another one..  I have the Chilton manual  1959-70 and it seems to be short of what I might need.  I must say anything I can learn is a plus..Thanks- jack

[garymand]

yes they are the same and yes there are more than one term for several components.  http://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour shows the valve.   http://www.sl113.org/wiki/Documents/BBB  is the manual one of 2 you generaly need.
The volume is volume flow--minimum of 1 liter in 15 seconds.

[ja17]

What would be especially useful to the diagnosis would be to have the gauge connected when the problem is occurring.  A drop in fuel pressure would indicate a fuel delivery problem. 13 to 17 lbs is sufficient to run the injection. You may actually see the fuel pressure drop-off right before the problem starts.  Doing the fuel flow test may also indicate a fuel delivery problem, especially when the problem is occurring. The fuel flow test is conducted with the engine off, ignition on.

[jackhughes81]

Joe,

Again I am heading to the supply house for a way to connect into my fuel line at the cold start valve.

The hard line compression fitting is giving me great troubles.  I tried to attach a pressure gauge there, but am unable to get the right fittings.  I took the csv coupling ( with the little return spring) off and am bringing that with me to indicate the male compression fitting needed.  I will then connect a female fitting for the gauge and hope to measure pressure.Could this be done somewhere else--  what would a gauge on the pump outlet measure..  static pressure but is that feasable or useful?  thanks- jack

[ja17]

Hello,

I just use a rubber fuel hose and a hose clamp to connect to the line on the engine. Just slide the 17mm fitting back and clamp a rubber fuel hose on the metal line. The pressure in the system is less than 20psi. At the gauge end you should be able to find a standard  fitting which will accept the other end of the  rubber fuel hose and clamp.

[jackhughes81]

Thanks a lot. I will try this today...jack

[jackhughes81]

Well, I measured the pressure and it was about 2 lb.. flow rate is about 1.5l/min.

However, this was done with the inlet to the fuel pump in a 5 gal can..  I did this because I could not remove the plug from the fuel tank.. it is rusted shut.  Bought an inline filter and will put it between the fuel tank and the inlet to the fuel pump.  This will allow me to put gas in the tank and produce head for the pump and filter it as well.
thanks again-- jack

[ja17]

Why are you using a 5 gal fuel tank for the pressure check?  If your fittings on your in line fuel filter are too small you will restrict fuel volume enough to have problems. notice that the fuel intake hose is around 12-13mm.

[jackhughes81]

I removed the fuel line from the tank to the fuel pump inlet.  I bought 3 feet of fuel line and attached to fuel pump inlet.  I placed the other end into the 5 gal gas can.  I placed the return line into the 5 gal gas can.  Any fuel line I am using is the same as the one originally running from the fuel tank to the inlet of the fuel pump.  In reading, I believe part of my problem is in this configuration, the fuel pump is 12 inches above the gas can, requiring the fuel pump to suck the fuel from the gas can rather than a positive pressure gravity feed from the tank.

Since the car died while driving last year, all my testing has been using a gas can since my thought was the gas tank is SEVERELY contaminated with rust and debris, hence the introduction of the clean gas source from the gas can.  Now I know that positive inlet pressure to the fuel pump is required, and in fact may be the cause of my lack of pressure at the cold start valve as I measured at less than 5 lbs.  As I mentioned, the flow rate I measured directly at the outlet of the fuel pump was just over 1.5L/minute.

In an effort to eliminated contaminated fuel supply, I have violated the fuel pumps need for pressure on its inlet.
My next test is place the 5 gal gas tank in the trunk and then run the fuel line down to the fuel pump.  My bet is this will work.  Next I will place the new, inline fuel filter directly in the fuel line from the tank to the inlet of the fuel pump.  I understand the fuel tank must be removed (already located the 3 bolts) and cleaned.

[garymand]

Why guess about problems that may not exist?    Pull your fuel gage through the handy access port in your trunk floor.   Inspect the inside of your tank.  Or just jostle the backend of the car, drain a liter of gas out of the tank supply line to the pump into a clear container, and see what it looks like. 

[ja17]

Hello Jack,

Dis-connect the metal fuel line at the intake starting solenoid. Slide the 17mm fitting back and just use a rubber fuel line  and clamp it to the metal fuel line you just dis-connected. 

[jackhughes81]

I could not get the sensor out of the tank.. nuts off but can not get the unit to budge.I know rhe sender unit never goes more than half full on the gauge.. 

MEASURED FUEL PRESSURE--  LESS THAN 5 LBS

Car will start then runs for about 1 minute then starts to sputter and make loud clunky type noises like valves and things are clanking.. then stalls..  let fuel pump run for a minute then starts and goes thru the same thing.. sounds like a fuel pump?  if so, can I rebuild, or I think I should be able to get some modern pump that will supply the pressure and volume?  please advise :'(

[jackhughes81]

I am slowly working on my fuel pump problem.. rain here has hampered, so its OK.. I have some quesitons about the pump.  Although others might know, I noticed you were responding and maybe had a broad knowledge of these related

1/ Is there a reason I can not use a universal pump  ($150)  that puts out 1.5 gpm at 35psi?

2/ Does the pressure relief valve take care of constant overpressure, or is it a bad idea to have more pressure?  what is too much pressure?

3/ The new pump draws 9A.  Old fuse was 8A.  Is this an issue, and seems like I saw somewhere the old fuses need to be updated..

4/ Is BAD GROUND a common issue with the 230?  How can I tell..?
 
thanks for any input..  My car sits just itching to drive when the sun comes out.. jack

[jackhughes81]

Joe,
STATUS: The car started and runs for about a minute then stalls..  very much like starving for fuel...  I measured fuel pump pressure at less than 5psi, found replacement for about $700 but cant do that right now.  So I bought and installed an aftermarket inline fuel pump putting out about 2l/min at most 35psi (max).  I installed with an in-line fuel filter between the tank and new pump.  The car does start but runs very poorly, no misfires but very slow RPM (1000) and very rough.  No backfire or smoke cloud from exhaust.  Steppinig on accelerator does nothing.  I have checked the return fuel line and its flowing.  My question is simple.. is there too much volume and pressure for the FI pump to handle?
I have posted but still need some answers to the question of what is the acceptable input range to the FI pump.  There is no fuel in either the crankcase or the FI pump oil reservoir.  I have change the FI pump oil (black sludge) with synthetic.  I have tried to lean and enrich the FI pump (keeping records of the movement) to no avail.  I have disconnected the cold start valve in case of leakage into the intake manifold. 
Remembering everything ran fine (but for the apparent fuel starvation from a faulty fuel pump) prior to my replacing the fuel pump, any suggestions on how I should proceed?
jack

[ja17]

Check the fuel pressure with your current set-up

[County Guy]

Hi, everyone.  I have been reading this thread with interest as I have been experiencing similar fuel problems with my car.  I have been working to bring it back from 'near death' for about 4 years now.  It is almost ready and, like Jack, I'm eager to take it out for a spin.  Unfortunately, on two occasions it has left me stranded not far from home.  Once i managed to coast to a safe parking spot and leave it til the next a.m. when it started up fine but only just made it home.  The second time I had to have it towed.  I always starts up cold and will idle indefinitely running beautifully in the garage.  On the road, however, it runs for about 6-7 min. at 55 mph before exhibiting signs of fuel starvation.

So, here's where I'm at:

I had the fuel tank reconditioned by a professional tank specialist.  I have looked into the flowerpot and checked to ensure that the inlet hole under the return line is unobstructed.  It is.  The tank is full of gas so supply should not be a problem.

The fuel pump that came with the car was crap so I purchased another identical and used parts from both to rebuild the one.  The pump will easily fill the litre bottle in 10 sec. (both on the bench and mounted).  The little filter and the 'return fuel check valve' are in place on the pump.

The pump will NOT produce more than 6 psi (usually 4.5) before the filter.

The (CSV) and the (WRD) seem to be fine.

This is were I get lost.  I don't want to buy a new fuel pump only to find that this is not the problem.  I have seen how the pump works and I don't see how a rebuild could increase the pressure.  The fin tolerances and the rpm are predetermined.   Also, why will the car NOT start if I run the pump for a few min. to retore the supply before restarting? 

So, Is there something else I can look at before breaking down and sending the pump off to be rebuilt or buying a new one.  What do you think?  I've run out of ideas.

How did you make out, Jack?  Did find a resolve to your problem?

Thank you for any help you can give.

Lockie

[ja17]

Hook the gauge up at the engine. Unscrew the metal line going to the intake starting valve.  Clamp the gauge on the end of the line.

[glenn]

How about the CSV line?  Put the gauge on the line at the intake manifold.  If you have 15 psi there, you're in good shape...

[stickandrudderman]

JA17, you are a very patient man!

[glenn]

Somewhere I vaguely remember from MB literature the return check valve was to 'smooth out' and hold 15 psi.

[County Guy]

Thanks for all your help.  I will do as you suggest.  Would an increased psi at the CSV mean that the injector pump raised the 4.5 psi entering in from the filter to a higher psi at the CSV ?

PS.  I believe the check valve at the fuel pump merely prevents fuel from reversing it's flow when the pump in not in use.

Lockie

[ja17]

The original electric fuel pump is capable of producing over 30 psi of fuel pressure. If  you pinch closed or block the fuel return line, you should see the fuel
 pressure rise from around 15 psi. to  over 30 psi.  The pressure in the system is automatically lowered to around 15 psi by allowing most of the fuel to return to the fuel tank via the return fitting on the fuel injection pump. This fitting is designed to perform as a basic fuel pressure regulator. The early 230SL injection pumps had a more complicated fuel regulator built into the return line. It had a spring and some moving parts.

Your engine will never run correctly with fuel pressure less than 10psi. If you have low fuel pressure, your problem could be the result of several factors;

...........non original electric fuel pump not up to specs.

...........original electric fuel pump, not working properly and not up to specs.

............fuel supply problem (sediment in tank clogging fuel flow into flower pot, clogged tank screen, clogged electric fuel pump screen, clogged main filter, no fuel tank venting, electric fuel pump hung too high)


............improper, non-functioning or missing fuel regulator on the return line of the injection pump allowing large volumes of unrestricted fuel to return to the fuel tank.


Now if you have low fuel pressure, try pinching closed or blocking the return line to the fuel tank then take a fuel pressure reading. Your fuel pressure should rise to over 30psi.  If it does not, you will have to check all the items listed above.

I recommend using an original electric fuel pump or a rebuilt one. Very few aftermarket pumps work out. However there are some economical alternatives than can be used in case of emergency or in case originality is not an issue. Stick has used the later Bosch high pressure electric pump with success. Review his threads. Also the Carter #GP4601 HP will work and can be found easily and cost is around $100.00 US.  In every case, the electric fuel pump must be mounted level with the bottom of the fuel tank since fuel must be "gravity fed" to the electric fuel pump.

Keep us up to date.

[m300cab]

change all fuel line filters
DON'T FORGET the Fuel Filter Screen just before the Fuel Pump next to the gas tank
there is a screen in the tank and a screen screwed into the FUEL PUMP
this one had 3 mechanics stumped, paid $950 to experts , only to stumble on the problem myself
back in 1993!!!