1985 380SL starts and stops immeadiately - PeachParts Mercedes-Benz Forum

zebby · #1 07-20-2010, 08:30 AM

My car starts and stops immediately. The car had been sitting for for a number of years so I replaced the furl pump, filter and spark plugs. I also pulled the fuel tank cleaned, and resealed it as it had some rust, The in tank filter was changed at the same time. I am reasonably sure the cold star injector is the only source that the engine is getting fuel from. I have not checked the fuel pressure however I did confirm that fuel is getting to the injectors with what appears to be good pressure.
What would be potential sources that would prevent the engine from getting fuel after starting?

ctaylor738 · #2 07-21-2010, 02:33 PM

You need to check your system and control pressures. I suspect that you have high control pressure and the air sensor plate can't move the piston in the fuel distributor.

zebby · #3 07-23-2010, 04:54 PM

Chuck, thanks for your response, I appreciate. I think you are correct. I pushed down on the plate and the car stayed running. How do I check and adjust the pressure?

ctaylor738 · #4 07-23-2010, 06:01 PM

You connect a gauge between the warm-up regulator and the fuel distributor where the larger line connects to either of them. Most gauge sets have a shut-off, which you position on the WUR side of the gauge.

Unplug the electrical connector from the WUR. Jumper the fuel pump relay sockets 30 to 87 to make the pump run.

With the valve closed, you will see system pressure, which should be 5.8 bar.

Open the valve to see control pressure, which should be 1.4 bar with a cold engine. Connect the electrical, and you should see the pressure come up to 3.8 bar after a couple of minutes.

The lower the control pressure, the more fuel is supplied with a given amount of air flow displacing the plate.

If you see CP = SP. There is a mesh filter in the WUR inlet that may be clogged. You can fish it out with a pick, separate the layers and clean it. Very common in cars that sit. Try a search - several posts on this.

zebby · #5 07-24-2010, 01:28 PM

I bought a fuel pressure tester but it did not fit. I was able to clean the mesh on the inlet to the WUR. It was a bit dirty but not too bad. I was also able to keep it running if I pushed down on the piece under the air cleaner. I tried to check for current at the idle control valve and the WUR but there was none. I hope to pick up a fuel pressure guage that will work this afternoon. Does anyone know if there should be power at these locations if the engine isn't running?

Build · #6 07-24-2010, 08:49 PM

There should be 12v to the idle control valve while the engine is running. I think the WUR only has power during warmup and when the engine is under heavy load.

ctaylor738 · #7 07-25-2010, 11:40 AM

The only thing the WUR uses the power for is to heat the bi-metallic strip that bends to change the control pressure.

According to the wiring diagram the WUR is powered on the same circuit as the pump. So it would get power when the starter is cranked or the engine is running (or when you jumper the pump).

I was surprised by this, I always thought there was some sort of thermo-time switch involved.

zebby · #8 07-31-2010, 06:21 PM

I finally hooked up a pressure gauge between the WUR and the fuel distributor and got about 140 psi for the control pressure reading. What should I be getting here? I know how to adjust the pressure however I am afraid that the high pressure maybe due to a return to the fuel tank being partially blocked and causing the high pressure. Remember now I cleaned and sealed the tank with POR 15. When it dried I realized that some of the openings were plugged so I used a small drill bit and cleared them but I am unsure if they are as clear as they should be. If I adjust the WUR to get a good reading and any of these opening are not totally clear will this cause other problems?

Build · #9 07-31-2010, 06:42 PM

Build · #10 07-31-2010, 06:45 PM

Ouch, looks like you're way too high at 9.65 bar.

abiby · #11 07-31-2010, 10:48 PM

Quote:

Originally Posted by zebby

I finally hooked up a pressure gauge between the WUR and the fuel distributor and got about 140 psi for the control pressure reading. What should I be getting here? I know how to adjust the pressure however I am afraid that the high pressure maybe due to a return to the fuel tank being partially blocked and causing the high pressure. Remember now I cleaned and sealed the tank with POR 15. When it dried I realized that some of the openings were plugged so I used a small drill bit and cleared them but I am unsure if they are as clear as they should be. If I adjust the WUR to get a good reading and any of these opening are not totally clear will this cause other problems?

Oops... That plugged return sounds like a likely guess. The return line on the tank doesn't directly enter the tank and I doubt you could open with a drill bit. Of course it's easy to check. Just pull the hose off the tank. If the tank doesn't drain a full stream, you've found your problem.

ctaylor738 · #12 08-01-2010, 11:22 AM

That reading is 6x normal and 'way beyond anything that you can correct. Even if you could correct it, you would be at risk of the line becoming unblocked and then you would have a huge rich-running problem.

You need to find the problem and fix it.

zebby · #13 08-01-2010, 06:12 PM

The return is blocked. I will pull the tank and clear it. Thanks all for your help, I appreciate. Once I have cleared it I will report back on the result.

RadioTek · #14 08-02-2010, 11:52 PM

Before you go to the trouble of taking the tank out

, you may want to check the 'plumbing' first. Such as a blocked tube or stuck valve. Eliminate the 'simple' stuff first. You may find a 'cheap' (for Mercedes values thereof) fix, and you'll learn the system to boot.

rocky raccoon · #15 08-03-2010, 05:06 AM

Roger what RadioTek said. Debris will clog the system at the first restriction in the plumbing system. In this case, if the line is clogged it will be at the exit point from the tank or upstream from there. I believe there is a filter screen at the line exit inside the tank. Requires draining the tank to access.

My third ex-wife sugared the fuel tank on my Harley and all it did was clog the fuel line where it exited from the tank. Didn't even reach the filter let alone "ruin the engine"'. So much for that urban legend. Dumb Biltch.