1991 300e Bad Computer? - PeachParts Mercedes-Benz Forum

latief · #1 05-09-2010, 02:43 PM

This is a friends car, excellent dealer maintained 1-owner car.....180,000miles

car developed a series of problems recently: terrible gas mileage, bogs down upon acceleration, eventually it started to die.......

I suspected EHA, but it seemed nice and dry....eventually, we towed it to a Mercedes shop...they said, the coil for the fuel system was bad, and they changed that....now car starts and runs, but has a little bog upon acceleration and terrible gas mileage....shop says computer loses control/stops functioning after engine warms up.....does this make sense? this is a respectful shop, and they are looking for a cheap replacement computer now....but i have a feeling that it is something else, as i never heard of this before....

all the usual: wires, cap, plugs, 02 ...etc are new .....

thanks,

JohnM. · #2 05-09-2010, 02:53 PM

I had similar problems in my 1991 300E and it turned out to be the ECU. When it goes bad, it will default to a fixed AFR, it will not take into account any of the various inputs/sensors in the CIS system. The computer really never has control once it goes bad. The car is in open loop when it's cold, and the car is in open loop when it's hot.

The weird thing about the ECU's on these cars is that they almost always allow the car to be driven, whereas when the engine ECU fails on any other car, it's deader than a doornail.

Also on my car, the EHA was bad. It didn't leak externally though! When I put a volt-meter on it, it was pegging at full voltage when you opened the throttle. Replaced it with another EHA and now when the throttle is opened it doesn't peg.

I went from failing emissions by nearly 5000% (biggest failure the testing guy had seen), to passing with flying colors by replacing the ECU/EHA.

latief · #3 05-09-2010, 03:22 PM

thanks,

so it is possible...good to know, i was worried it was a symptom of something else.....hopefully he will find a used one for cheap. the dealer quote was a couple of thousand dollars which is not going to happen.......

the shop says EHA is good, so i would assume it is.......hopefully this ecu swap will fix the problem

latief · #4 05-20-2010, 10:09 AM

So the car is still at the shop....Terrible situation !!!!

someone did a number on this car. The current shop changed the computer, but something was wrong....the car had a backfire, so upon inspection, they found the timing to be 2 teeth off! so they corrected the problem, and went ahead on adjusting engine and transmission shift points...

My friend was supposed to pick up the car today, the mechanic was still fine tuning yesterday. this morning, the tech took it for a final test drive, and one of the fly-wheel bolts came loose and did a number of the crank position sensor, and starter....etc......?!?

I guess the dealer who worked on the transmission previously did not torque the bolts correctly, and with the increased torque after engine repair, one of the bolts came loose....

this is a nightmare !

JohnM. · #5 05-20-2010, 11:51 AM

Sounds like a basketcase

tinypanzer · #6 05-20-2010, 06:26 PM

Yikes.... As to the original problem you posted on, engine coolant temp sensors are a good candidate.

latief · #7 05-20-2010, 06:50 PM

Just came back from the shop.

The engine is running perfect after the computer replacement. it was in fact causing a lot of problems in addition to the timing issue....

Now to the new problem. The tech found an extra fly-wheel bolt in the fly-wheel area..none are missing, there is just an extra one!!!. I guess it was lodged in there and came loose, it destroyed some of the tabs on the fly wheel, and as i said, the starter gear....

Now the mystery is, why is there an extra Mercedes labeled bolt in there? And why did it decide to come loose after all these years? The tech thinks that the transmission has been pulled before....hopefully not by the same people who did the timing.....maybe they forgot a bolt in there

I will need to talk to my friend, and see what service records she kept. I am curios to see who did all this wonderful work before...