well my problem came back today...When my car reaches normal operating temp and If turned off.It will not start until its cooled down(actually it will run for 5 seconds then shut off).It even shut off on me twice while I was driving...The last time it did it at a gas station I unplugged the ecu and it started right up.It ran ****ty but it was running.So I guess i need a new ecu.

The bosch part #0 280 800 304 /mercedes#008 545 16 32 These are the two part numbers on my ecu.which is off a 1989 300cE

there seems to be a **** load of different ecu numbers for these cars.I found a couple of bosch#006 545 64 32 which is for a 1989 300E.Does Anyone know if its possible to swap these ecu?

 

Any luck with this repair? Your problem sounds very familiar and I may have some direction. Let me know if this is still an issue. I don't believe it is the ECU.

 

Ever since I messed with the EHA it hasnt been a problem.I doubt if this is the perminent fix so. Im still interested in what you might think it is.

 

when mine did this, it had a bad temperature sensor for the ecu. It would only do it when warm, then stall and not restart. Check the rear temp sensor for resistance, you should be able to find the numbers through the maintenance cd.

 

Well, this is just a possible remedy to your problem. There could obviously be quite a few additional with that symptom.

I believe your car still had the old style fuel pump relay and not the MAS relay. I remember the MAS starting in 1990. I could be wrong.
I had several old style relays with a failing solder joint for the main pump relay contact. It appeared the heating and contracting caused the joint to crack around the pin that was soldered. When cold the contact was sufficient. When the joint heated after driving, the car would die and the joint would need to cool before restarting. This failure was easily visible and cured by reheating and resoldering the connection. I fixed many cars this way and it's easy to pop the outside cover from the relay. Just reseal after inspection with your regular goo. I fixed more relays this way than I saw fail for other reasons.

 

I do not think you have conclusive evidence it is the ECU. You unplugged and it started up. That could also mean some sensor is feeding the ECU (bad) data so the car does not start.

 

I'm sorry, there is no "data" being sent to that control unit. It is strictly anolog input. The computer looks at the input as it's available. This stuff is very simple in it's function compared to new cars. Don't give these old CIS systems too much credit.

 

"Input" is data. Data does not have to be digital. For example, a temperature input via resistance measurement is data.

 

I replaced fuel pump relay....I even purchaced a temp switch but they sent me the wrong one.

 

did you replace the fuel pump, my straight 6 jag did that right before the fuel pump died.

 

I kinda don't think it is the ECU either. If it were me, I'd stash the ECU in the trunk for a few days to see if the problem still exists. You will be in basic CIS which means power, cold running and mileage will suffer, but it will run. My wife drives a real nice 89 300CE. I like the car for its simplicity. I can jumper the fuel pump relay with a paper clip and disconnect the ECU to finish a trip or get it back home. Somewhere in 90 they went to the MAS unit which controlled fuel pump, A/c, and oxygen sensor. It got worse in 91, because everything got incorporated into the ECU. If that thing takes a dump on a trip, you're screwed until you get towed in and shell out a couple of thou.
Good luck and keep us posted.