Mercedes 300 SEL - Dies after short run time

[srbonne]

Hello - I have a 1988 Mercedes 300 SEL. This car will sstart up and run like a champ. After about 5 Miles it will suddenly die. There will be no power from the engine at all. The tach will drop to 0 but all of the auxiliarys will stay powered up.
I replaced the Fuel Pump relay, ran the car and had the same result.
I then replaced the 10 A fuse in the OVP, same bad results.
I tested power at the fuel pump:
When it is runnning there is 13 V across the terminals,
When it is dead there is 0 V across the terminals.
Three months ago I replaced the alternator that was putting out about 4 V and the fuel filter.
I have spark at the plugs, and replaced the fuel distributor solenoid (EHA?).

If anyone knows the fix to my problem I would be greatful for their input.

[mbshop]

do you have 13v at the pump while cranking the engine? how is the spark? how is the fuel pressure and flow when this occurs?

george

[srbonne]

Yes 13 V when cranking the engine.
The spark seems strong.
I do not have the gauges and tubing to test the fuel pressure

[mbshop]

scott, the fuel pressure readings are very important. i think its time to go
to a shop that understands mercedes and let them check it out. might be cheaper at this point.

george

[srbonne]

Thanks George -
I am thinking about replacing the OVP this evening before I go that route. I have had it to the shop twice already and they could not figure it out as when it was there it ran fine.

[ctaylor738]

Try bridging pins 30 and 87 on the fuel pump relay socket and see if the problem still occurs. If it does, then it rules out the inputs to the relay (like RPM). If it fixes the problem, then you have a couple of specific inputs to check.

Do not drive the car any more than necessary like this, since the fuel pump will run regardless of what the engine is doing.

[Steve Gutman]

I had a similar problem. After the car warmed up it would die. It would start up and run bad. If it sat and cooled it would run well again. My ignition control module was very hot to the touch. I replaced it and it has not died since.

[srbonne]

OK Guys- I have now replaced the fuel pump relay and the OVP ( with a newer style relay with 2 fuses?). Still the car will not start and there is still no voltage to the fuel pump while turning the car over. What is the next step.
P.S. I can not check the fuel pump pressure as the pump will not run.

Does the master out there have the answer?

[srbonne]

I bridged 30 and 87 and the fuel pump and the car fired right up and seemed to run fine. what are the specific inputs you speak of?

Thank you.

[jmyers177]

Scott, I am having a similar problem with an 86 300E. I am thinking I have an ignition problem because when I got the car back home I gave it a short shot of ether and still had the same symptoms. After it quits, it seems to be firing almost randomly when trying to start as it kicks back, belches, and tries to fire occasionally. It will always crank up and run perfectly for about 5 or 10 minutes and then dies. I haven't checked the ignition module for extreme heat as mentioned but am thinking the ignition module or the crank speed sensor may be acting up. My next step is to warm it up and put a timing light on and see if I can tell what is happening to the timing. If I have to replace the ignition module, based on the price of the bosch unit or replacements, I think I will try to go to a Crane or other after market unit. Then I hope to find someone that has been there before. Looking at the Crane XR700 as a possibility.

Good luck and let us know what you find.

John

[srbonne]

Any one? Is replacing the ignition control module the next step?