I have a 1987 300E. I've been having a problem lately with stalling. It happened over a year and a half ago, and I replaced the fuel pump relay, after reading the forums here. It went for awhile without any issues, but recently, its cropped up again.
About 6 months ago, it started running bad. As in, surging at a stop, abs light on, and srs and O2 sensor flashing on/off. After awhile, the lights would stop flashing, and the abs light would stay on. Sometimes it would even go out. There doesn't seem to be any rhyme or reason, it did it on a hot day as well as a cold day, and at any time. sometimes it would do it every day, other times it would go for a few weeks without any problem.
The car became increasing hard to start, it would take several tries to start. but it would run , abs light on.
Then within the last week, it began stalling, most times it would start back up, but a few times it would not.
I began thinking it was the fuel pump relay again, but these parts should not wear out after 18 months?
I again searched the forums, and I saw OVP relay. I checked the fuse, and it was ok. I took all the relays out, and took the bracket out, so I could examine the wiring. I did not see any broken or loose wires, so I reinstalled it. It started up ok, and ran, but abs light was still on. I kept restarting it and running it for awhile and shutting it off, to see if i could repeat the problem. Nothing. Then I saw the one post about resoldering the connections on the OVP circuit board. So I pulled the relay, and took the cover off, and resoldered the terminals. I reinstalled the relay, and first, without the fuse, started it up. It started but ran rough. I popped the fuse in, and it evened out, and the abs light went off. It hasn't come back on, and I haven't seen the other lights blinking at all. It runs better than it has in months.
However, when we first start it up now (cold start, first thing in AM), it stalls, or gives us a hard time starting it. It then runs, and may stall out one more time. But then it runs fine the rest of the day. No lights blinking.
My question is, could the OVP still be bad, even though I may have corrected part of the problem by resoldering it? It is my understanding that the OVP controls the fuel pump relay, as well as powering the ABS control unit, and also the cold start circuit on the ECM. Seems this is the only time there is an issue, is 'cold start'
Advice? suggestions? Please help! Thankyou!

 

I had a similar situation a month ago...I tookmy battery out, replaced the black plastic cover behind the battery to find a 1 square inch relay with a red colored top and a clear plastic cap with two 10 amp fuse which I believe is an OVP (Over Voltage Protection relay). I checked the fuses without removing them andseem to be just fine, but when I removed both fuses, checked them with a multi meter,Ifound one of the fuse with a hairline fracture. I changedthe 10 amp fuse, place the battery and started the car and it started right away...ABS light off...and everything was fine from then on...I am not sure if our cars have the same configuration buthope this helps in anyway.
Bob

 

Well, I spent more time under the hood looking for a broken wire, etc. I think I finally narrowed it down to the Fuel Pump Relay, again. I had an old one, from whenI replaced it last year,and I resoldered what looked to me to be the bad contacts. I put it in, and could hear the fuel pump hiss, but no start; almost like the ignition wasn't getting juice. I put the other relay in and no fuel pump hiss. While my wife started the car, I jumpered 7 and 8 on the relay, and the car started. As soon as I removed the jumper, the car stalled. So this tells me that the relay i just bought last year was bad. I took the original one i had been soldering on, and I looked at it again. I found 2 contacts where the copper foil on the circuit board had seperated from the solder. so I repaired that. Put the relay back in, and presto! fired right up. let it run. shut it off after a while. It still starts. I guess the big test is going to be in the morning. I'm going to order another, this time from the autohausaz web site, instead of going to the dealer. Hopefully this doctored one will get me through till it comes in the mail. Anyone else have these fuel relays go bad in a year? Maybe it went bad because the OVP was not working properly? Car runs great now. I guess I'll have to keep a soldering iron in the car.

 

Wraith6988,

I had that problem with mine about a ear ago, my fuelpump relay lasted about 2 weeks.I came to find out that my O2 sensor wire had been rubbing on the drive shaft shorting out the fuel relay.Check that and see if it helps.