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300 CE warm start problem

Knowing in advance that this group is no place to ask for diagnoses beyond the simple things, I nonetheless ask for advice. This is because no independent garage nor the Mercedes dealer has been able to diagnose a long-running problem.

The car:

1990 300CE 24 valve, 202,000 miles. Starts fine, runs strong, good compression. Owned for 11 years.

The problem:

The car starts fine in the morning and runs great. However, after sitting for anywhere between 15 minutes and 3 hours, upon starting, the car will immediately die. Cranking again starts the car right up, and all is fine.

I first thought it might be fuel starvation, but it's been suggested it might be just the opposite... fuel flooding. One or two mechanics say the original fuel distributor may be leaking fuel slowly into the air horn when it sits, and when warm, the car then dies due to this flooding-like situation.

It sounds plausible to me, except for another symptom which is this: While driving, and only occasionally, when I get off the gas as when coming to a stop or going around a curve or corner, the car will simply die very quickly, as though suddenly starved for fuel. Again, turning the key starts it right away, and all is well.

If the warm-start problem is caused by a tired fuel distributor, then I don't know how it would cause the second problem.

What I've done so far:

? replaced the original fuel pumps (which were tired) with new OEM ones ? replaced fuel accumulator and fuel filter

Neither had any effect, except the pumps are quieter and it's good to know they're new.

Any suggestions would be appreciated, including mentioning which other bolt-on components could cause such a problem

Thanks!

C. Adams

(replies to the group, please)

Reply to
Charles Adams
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On the one hand seems temperature related but on the other hand seems voltage related when engine alternator is at low rpms.

First suspect is the fuel pump relay (voltage related). Second suspect is the over voltage protection relay (voltage and engine temperature related). Third suspect is the O2 sensor and the wires to it (intermittent and excluded at cold start). Fourth suspect is the ignition coil, if motor has only ONE coil.

Flooding is proven by wet spark plugs; I doubt that's the case here.

Reply to
Take A Guess

You might have an internal fuel pressure leak. The fuel injection system must have pressure to prevent vapor lock after the engine is shut off. The problem could be in the fuel accumulator (likely in rear passenger side of car), or it could be in the fuel distributor, under the air cleaner. There may also be an anti-siphon valve to prevent fuel from running back into the tank after shutoff. If that valve is defective, you would have a similar problem. Search this group for those items and related problems.

Reply to
coolmale48

I would say your got internal pressure leak. Depending on what fuel injection system you have as this model year may have two different versions... If you have electronic fuel injection, then one of your fuel injector is leaking.

If you have a fuel distributor, then you can have an internal leak at the compensator valve.. which is on the top of the fuel distributor... underneath the big bolt, or torx head.

In both cases, you can also have leak at the accumulator by the fuel pump... one side has a rubber hose, disconnect that and if fuel keep coming out of the accumulator (not the hose), it is bad.

Reply to
Tiger

Good to see a new face in the group with such encyclopedic knowledge ;)

Ximinez

Reply to
The Spanish Inquisition

What is your idle mixture ratio sweep with lambda in closed loop?

More than likely it is 60-70. Too lean. Richen it to 40-50 and it will fix your problem.

Reply to
Karl

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