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)

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.

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.

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.

Take A Guess wrote:

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

Ximinez
--
Our three weapons are fear, surprise, and ruthless efficiency...
and an almost fanatical devotion to the Pope....
http://www.ai.mit.edu/people/paulfitz/spanish/t1.html
http://www.youtube.com/watch?v=gldlyTjXk9A

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.


"Charles Adams" <me (AT) mymac (DOT) com> wrote