124 300CE-- Warm Start troubles

My 91 European version 300CE (104 Motor) has trouble starting once the engine is warm. The symptoms are as follows

1. Always starts on the first crank when cold.

2. Always starts and stalls if warm and sitting for more than 30 minutes (Will start and run perfect on the second crank)

3. Always starts on the first crank if warm but has been sittting less than 30 minutes.


* All starts are with no foot on the pedal.

** Turning the key to on and waiting for 20 seconds has no effect.

*** If I give the motor a little throttle once the engine catches, It will stay running on the first start. I have to give it enough throttle to rev to about 1500 rpms and let it down easily or it will stall.

**** The car seems to run a little rich.

I'm pretty sure this is fuel related but any help on where to start diagnosing this problem would be greatly appreciated.

Thanks

Chris

[Ashman]

My car was doing the same thing.

I changed plugs and it didn't help, so I used some techron, and tried gas from another station, and it seems to have subsided. I think there might be some bad gas floating around in places.

You can also look into your OVP. I did not change mine, I just kept running premium fuel form different stations until I found one that the car started operating normal on. My car has since stopped doing it.

You may just need a simple "Italian Tune-up.." hehe

I did notice that since I decided to drive the car harder for a bit, it has been running better. it could be mine was related to some carbon build up. But any of the above mentioned stuff should give you some ideas of whatt o look for.

Alon

Post some pics of your car if you can, I want to see it.

[michael_vogt]

Hello Chris,
possible cause are the injectors. If they get older deposits can be formed at injector nozzles and the injectors can start to leak after you switch off the engine. Then you will get a fuel vapor problem in the injection lines causing the described hard start of the engine.
Try some chemical fuel additives e.g. Techron or Liqui Moly Injection Cleaner best together with an Italian tune-up.
If this will not help you can test the fuel system for internal leakage. The fuel pressure should not drop below 3.4bar after switching off the engine. Else you should renew your injectors.

Best regards,
Michael (86, 420SL)

[Dan]

Chris, I am currently trying to work through the same problem on a 1989 300CE, US version (103.983 motor) . In fact, it's in a 2nd shop for further diagnosis as I write this.

There's an MB bulletin on hot start problems for the 124. It lists several items as possibilities for 'customer complaints of hot start difficulty,' including fuel pressure leakdown (possibly the injectors as Michael mentioned, but also possible: fuel pressure accumulator, fuel pump check valves, cold start valve, injectors, and fuel pressure regulator), zero position of the mass air flow sensor in the fuel distributor, and the coolant temperature sensor (not the gauge, but the input to the EFI module).

I gambled and tried, but failed, to solve this using just the parts replacement theory. New OVP relay, fuel pump relay, fuel accumulator and fuel pump check valves were installed to no avail. (The EHA was replaced a year ago for other reasons.)

If you have the MB 124 manual on CD, it goes into detail on all of this.

A fuel pressure leakdown test isolating the leaky segment of the fuel system might be your best bet, assuming it is a fuel problem.

Hopefully, I will know later in the week the cause of my hot start problems. I'll put this on my original post, which was a few weeks ago here.

Good luck!