Hello everyone, its great to find people online who love Mercedes.
I have owned many over the years, starting with a 1969 280SE.
I now have a 1991 300SE which has run very well until a few days ago. I need any help that you can give me.
My problem is as follows. The car will start and run very well to the shops about 2 miles away. After I come out and try to start car it will not start. I did eventually get the car to run by putting the accelerator peddle to the floor and holding it there. It reluctantly started after about 20/30 sec cranking. On the way home it would misfire/stumble it I put the accelerator peddle down to hard.

This sequence will repeat if I let engine get cold. I have tried pulling of plugs from Temp sender and what I think is the idle control when engine is running and it makes no difference to the engine running. I am at a loss as to what could be causing this. I need desperately need any help that can be given.
Cheers, Brian.

Possibly a problem with the overvoltage relay not providing power to the ECU.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Hi, where is the overvoltage relay and what pins should have voltage etc.
Many thanks, Brian.

I would suspect a faulty Oxygen sensor.

__________________
Fred Hoelzle

O2 sensor has NOTHING to do with starting!

Overvoltage relay is near the brake booster & has a red 10A ATC fuse in it.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

From my experience with that engine a faulty Oxygen sensor results in hesitation/stumbling when accelerating.

__________________
Fred Hoelzle

I had something similar and it was due to the Bremi rotor arm that was only 18 months old. Replaced it with the original MB part (250K Kms old) and it was fine. I now have a new MB rotor and cap.

Bon courage.

RayH

From my experience best to use Bosch distributor cap & rotor and Beru ignition wires.

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Fred Hoelzle

I now have MB original (maybe Bosch but I didn't look) cap and rotor teamed up with Beru wires and plugs. Seems to work.

RayH

Hello to all, took dissy cap of today and what a mess. The rotor also very burnt. I do not know how it ran so well for so long. Have ordered and will arrive in two days. Will report back then.
Cheers, Brian.

Anyone got a theory on why heat would affect the distributor cap and rotor?
Coil heat soak?
Expansion causing larger gap? Naw.
More spark energy needed in hot environment?
Mixture lean when warm, more spark needed to ignite?

Let us know how it works out. I have a heat-soak stumble that i can't find, so I'm always looking for solutions.

DG

Thanks guys, I will have a look at what has been suggested and report back.
Cheers, Brian.

Hi all, dissy cap and rotor arrived today. Fitted and no more problems.
Cheers, BrianD.