Weak Starting, Warm. W124 230E '92

Hi, I was wondering maybe someone here could help me. This car has a slight hard starting specially when warm.
When starting cold in the mornings it starts at first try, but weak,
hesitates at first but very soon comes strong. Later, after two - three hours beeing off, with engine T around 60C, it starts at second or third try, hesitating. But on the other hand, when it has been off for a short while, say 15 min, it starts at first try and strong.
The car has 90k miles on the clock, spark plugs, wires, cap and rotor were replaced recently. The fuel filter has 6k miles. The fuel pump and fuel accumulator have never been replaced. The cold start valve works fine, I think, I removed it and squirts fuel when the engine is cold, although I dont know if it is the proper amount.
I did a search and found out that maybe the fuel accumulator cant keep static fuel pressure for warm startings (vapor lock), but if this is the case, I wonder why the symptom appear on mornings, engine stone cold, and cold start valve squirting fuel.
Otherwise car running is almost perfect, the only other little problem is a slight unstable idle when warming up.
I would appreciate any idea.
Thanks in adavance.
Marcelo Mansilla
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I experienced somewhat similar problems with an E320 (after only 18K miles). Perfect cold starts but poor hot starts after an hour or more of being shut down. There was also a stench of fuel in the exhaust. Starting was much quicker if I stepped on the accelerator.
The cause was one leaking fuel injector which I found by removing the spark plugs after the engine was cold. One was wet with fuel.
So the motor was over fueled or choked from this leaking fuel injector.
The injector was replaced and the motor runs perfectly.
Hope this helps you diagnose your car's problem.
P.S. Try some Techron or similar fuel injector cleaner if you suspect anything with the fuel injectors.
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Hi Marcelo,
I have a '91 200E, the engines should be similar, and had almost the same exact symptoms. The mechanics suspected the fuel accumulator or the injectors too, but it turned out that it was the fuel pressure regulator that was the problem.
Regards, WS
Marcelo Mansilla wrote:

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Thank you for these ideas, I'll do my homework and let you know.
Right now I'm waiting for the engine to get cold, to remove the spark plugs and see.
At the same time, if I could, would like to check the fuel pressure regulator. Is there an easy way to check it?, does anyone know how to?
Thanks
Marcelo Mansilla
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The fuel pressure regulator is a small can connected to the end of the fuel rail. There's a small vacuum hose connected to it, going to the intake manifold. Pull off that vacuum line - if fuel dribbles out, the regulator is the problem. That fuel is flooding the motor. Otherwise, pull the spark plugs as part of your continuing investigation.
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Many thanks, that was what I needed.
Well, I find out the pressure regulator, disconnected the small hose and wasn't leaking any fuel, but there was somewhat liquid carbon sediment along the bottom of this hose. Maybe it's slowly leaking small fuel drops, or maybe it is the natural condensation of this area of the engine, don't know.
With respect to the spark plugs, they were all dry, so I guess that neither a leaking injector nor the pressure regulator are "flooding" the engine.
Just in case, I sprayed air intake cleaner on all the injectors. Idle stays smooth.
Tomorrow, I want to disconnect the rubber hose back on the fuel accumulator to check it. On thursday I will carry out a fuel pressure test on a shop.
Hope to find out something defective. I'm getting out of ideas.
Best regards
Marcelo Mansilla

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Ok, Today, checking the Fuel Accumulator:
Started the engine, then off. I dissconnected the rubber hose back in the fuel accum. What a mess, I'm soaked right now writing this :).... But, as it ought to be, gas was coming out from the end of the hose, there wasn't any fuel coming out from the end of the Fuel Acc.... so this device is fine.
Well, manometer will say last word tomorrow, nevertheless something is telling me that there will be nothing wrong with dynamic or static fuel pressure... Is there anything else to look at? ....Please...
Regards
Marcelo Mansilla

slight
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The question that ought to be resolved is whether the warm motor is fuel starved or over fueled. When that is known the suspects can be narrowed to a few.
Complaint: Slight hard starting when engine is warm.
Are you stepping on the accelerator when this happens?
If not, does the engine start immediately if you do step on the accelerator while cranking - even if only a small amount?
When opening the throttle causes an immediate hot start - no delay - indicates an over fueled condition (flooding).
Then the task is to find why a small amount of fuel is slowly leaking into the intake manifold.
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Last few days I was stepping on the pedal on startings. It doesnt improve, in fact it gets slightly worse. Does this mean that it's a poor mixture problem?... If so, what else to look at?
Many thanks

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