124 engine trouble ??stumped??
 

searched around a little and couldnt find anything so here goes... ok this is the first problem ive had with my 87 300 e thats truly got me stumped... once the car reaches operating temperature it basicly sputters and backfires under even small load, if i drive with very little throttle its a little better
but the longer i drive it the worse it gets, after a long drive at highway speeds (where the problem isnt as noticable) stop and go driving is very difficult and the car will even stall out occasionally, i thought it could have been excessive back pressure from a corroded resonator but after replacing the exhaust the problem still persisted (just more quietly) also tryed swapping out the ECU and cleaning the plugs (not fouled anyways) all to no avail... i was also suspecting some sort of transmission problem but the problem doesnt go away in park or neutral and the fluid level is fine anyways... not sure what to check next so any help would be greatly appreciated (i cant let my GFs car be better than mine)

Could be any 1 of 5-6 items causing that problem.
Coil, secondary ignition, crank sensor, overvoltage relay, & or fuel pressure,

hmm overvoltage relay could be, ive tried several of them but i havent tried changing it since the problem started... seems like every one of them i tried i still had pulsating lights. i dont know much about any of those other things but can they start suddenly? this problem started up without any real warning, thats why i originally thought it could have been the resonator:(

did you ever replace the plug wires? when they heat up resistance through them can skyrocket.

Have you looked at the fuel distributor? Mine acted that way after the car warmed up but ran ok while still cold. If it is a problem you may be able to disassemble and clean it. I got a factory rebuild from MB.

I think John nailed it.
I have seen alot of those cars act up when the coil wire and or plug wires heated up.
Try a new coil wire first and see how it does.
You can put an ohm meter on the wire and twist the wire around a bit to see if the resistance goes whacko or to an open circuit.

Check the fuel tank vent.........just an idea?

thanks guys i havent had a chance to check some of these things yet, but i did the plug wires along with plugs cap and rotor some time this past summer, could they have gone bad that fast? fuesl distributor sounds likely so ill have to look into that, unfortunately im about as sick as my car right now so i havent had a chance to do anything since the new exhaust was put in:( hopefully ill have a chance to try and figure it out this coming weekend. i need to get the new exhaust welded anyways.

::bump::

124 problems
 

I had a similar problem with my '87 300E with 130K miles. Baffles my indie for weeks. I mentioned it to my step son and he had the same problem on his Passat. He changed the COIL and the problem stopped. I did the same thing on the Benz. The problem went away. It is now a recommendaion of my indie that they change out the coils over 125K.
Anziani

'87 300E 175K
'95 E420 Sp. Edition. 101K

yeah several people have mentioned the coil so thats the first thing im going to check this weekend, also anyone know what the possibility that this could be the cats? you guys have been very helpful!!

ok well me and my friend are going to swap coils this weekend and if that helps ill go ahead and buy one, if not im going to take the temp on the high side and low side of the cat, anyone know what temp difference could mean a fouled cat? also the car passed emissions no prob when i got it a year ago so i wonder if the cats can go bad suddenly for some reason

These are the Exact symptoms I experienced w/ an 87 560 (same CIS-E), turned out to be a faulty KE control unit. Once the car was up to temp and the car went into open loop/regulated it lost it's mind.. The longer you drove the worse it got..no power, poping, burping, etc, etc.. You might try unplugging the KE..see what happens.

Jonathan

The 91 300E had similiar weird running problems. Finally took it to a good tech friend and he knew immediately it was a bad coil. Changed it and the car purrs now. Hell, it should for all the parts and repair attempts I did to it.

Haasman

if the KE control unit is the thing near the battery i already tried swapping it with another one i had lying around, when unplugged the engine would drop down to very low rpm but the same backfiring chugging etc. was still happening though i think bad control unit would cause similar symptoms, im still planning to try changing the coil tomorrow though... haasman i know what your saying,the only thing thats good about wild goose chase repairs is that after you finally find out whats wrong youve replaced so many things that the car runs much better but your wallet is :behead: !!!