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: !!!

Don't discount the cap/rotor.
 

John, I had a similar problem with my '90 300E. I had installed cap, rotor, wires and plugs 10k ago. Problem was I mis-fitted the distributor cap o-ring and it caused an improper clearance between the rotor and cap which caused massive arcing. It only did it after a long drive and was not noticeable at speed. Symptoms sounded like yours. Check out the thread "300E misfire when hot" last posted around 12/6.
Chuck.

http://www.peachparts.com/shopforum/showthread.php?t=171798

Here's my saga. Fixed by a cap and rotor after all else failed.

well i did my cap and rotor about 3 or 4 k ago, but that could be it. i remember putting the o ring i ordered in the groove but i dont remember any other o ring in there, tomorrow i will check that if the coil does not fix the problem. i had read that thread a while ago befoe i began this one and it sounded similar so its certainly possible. thanks again for all the help guys ill post tomorrow and let you all know what i find

You might also look for vacuum leaks. The idle air bypass hoses may need to be replaced. The rubber boot under the fuel distributor and throttle may be bad. The injector seals may be bad. It's an '87 after all.

Check the following links:

http://www.peachparts.com/Wikka/M103VacuumLeak

http://www.peachparts.com/shopforum/forumdisplay.php?f=82

http://www.peachparts.com/shopforum/forumdisplay.php?f=84

Just a thought.

tried replaced coil to no avail, but i plan to check out chucks suggestion tomorrow or later today if i have time, thanks for the help

Could be crankshalt sensor,that it screws up when it gets hot,also a big possability a coolant temp sensor. .

so the things so far i know its not...
coil
transmission
02 sensor
KE unit
plug wires
things it still could be
ignition module
still haven't checked the cap and rotor
cats?
vacuum leak
crank sensor

interesting, cap and rotor would have been the first thing I would have checked just because you can and it's fairly easy.

When were they done last?


Jonathan

Again....make sure your gas tank is venting.

My 560 front cat partially disintergated and rotated in its housing blocking gas blow. Systoms are different from yours. Highway is tough because the gases can't get through the blockage. stop and go was fine acceleration was gone. No back fireing or stuttering. Just no top end.

the reason i have delayed in checking it is it was done less than 3k ago about 6 months, and the problem didnt start until recently, but its next on my list over the weekend. how do i check the fuel tank vent? thats what i was wondering about on the cat, so maybe i can cross that off the list since the car passed emissions with flying colors when i got it and that sort of thing doesnt just happen all of a sudden does it? next stop, cap and rotor

Try this: Unplug the EHA and see if the problem persists. If the problem goes away, that eliminates spark issues and the mechanical part of the FI.

My daughters '87 300E had random bog and rich running issues. It's running fine w/o the EHA plugged in. Now to find the time to chase what's actually causing this.

unplugged the EHA and no difference, took the cap and rotor off and this could very well be the problem, theres some green stuff around the edges, and sure enough when i looked back behind the orange o ring i saw another black o ring that had hardened... any thoughts?

Sounds exactly like what I had. It looks like we both made the same mistake when replacing the cap and rotor. There should be one o-ring around the base of the "backing plate" (where you found the black one). I had installed the new orange o-ring and left the old, black one in place which apparently caused improper clearance inside the cap. I put new parts in and so far it runs great.
Chuck.

im awaiting the parts now, so much for 3 day shipping...:confused: the main thing is how long after you installed these parts did the problem start?? hopefully this will resolve a problem that has basically made the car un-drive able.

It took about 8-10K miles after the new cap and rotor for the problem to show up. It got worse over the next several hundred miles (I kept driving it-see thread). I guess it took that long for the internal arcing to degrade the function of the contacts inside the cap. I had lots of green crud around the terminals and the center post inside the cap was charred and crumbly. I bet you've found your problem. What threw me off was the different color and appearance of the new o-ring that I ordered. I now realize that it was the same dimensions as the black one and was supposed to replace, not supplement the black one.
Chuck.

AHA!!! llol that does sound like the same thing, just slightly different symptoms, however there is the same green crud and the same missing tip in the center, so how much and where should i use the dilectric grease? i just got the parts tonight so i want to try to put it together over the weekend. also is there anything else i should know about how tight this should all be and that there is only one o ring? i dont want to mess this up again :silly:

Oooo, don't know about the dielectric grease. And there is, to my limited knowledge, one o-ring that goes around the base of the "backing plate" (or whatever it's called) that seals the dist. cap to the backing plate. Just get the old black o-ring out and put the new (orange?) one in it's place. Or, if you bought a new backing plate, mine had the o-ring already installed.
It's funny how our situations are so similar. And I resisted the thought that it could be the cap and rotor. I believe it was gmercoleza that pegged my problem from the beginning but only after chasing a couple of other things did I check that out. Of course, it could have been several things and I did learn a lot about the car in my quest.
Good luck.
Chuck.

well i think that did it, put the cap and rotor on this morning and havent had a miss yet, it idles a little rougher than it used to but i think the plugs may be a little rough so im going to replace them again and maybe some seals as well, thanks to everyone in here whos given me advice!!

just a thought,vacuum leaks are much more pronounced at idle and tend to dissapear as the revs rise.while it's true that these cars suffer from marginal ign coils as they age i think your prob could be vac leak.find indie who can perform smoke test and ask to be there when it's performed.i think you will be amazed at all the places where the smoke is coming from.

possible but since it never idled rough before all this mess i think its because of carbon build up, im definately going to check that out though if i decide to keep the car thanks!