Stalled W124 -- alternator or wiring harness?
 

Thanks in advance for your help on this one.

My '95 E320 Wagon suddenly stopped running and I coasted from a stop at highway speed. The battery had power, but the engine would not restart. The battery lost nearly all its power after cranking the starter a few times and running the emergency blinkers, lights and accessories for about 5-10 minutes.

For about two days before this event, the engine was running roughly. The whole car vibrated at idle and low speeds.

The wiring harness is original, but not obviously deteriorating. Is it safe to rule it out as the cause for the stalled engine? Is this an obvious case of a dead alternator or could it be the diodes or some part in the electrical delivery to the engine?

Thanks again for your help.

your lucky if your original harness is not cracked to heck. thats the first thing that I would check. and if you need one. I have a harness-

Thanks. How much for the harness, and do you have the correct one for my model? I seem to recall 2 or 3 variations of the W124 harness. PM if you prefer.

Also, can I rule out an alternator problem since the battery still had cranking power left?

Well, the car that it came from was Mfg in 2/95 it all comes down to your Vin Sequence. you can take your car in to a parts place and they can measure your idle charging, otherwise you can use a multimeter and test it I think it should charge at 13.4v IIRC however I may be wrong.

if you feel like it shoot me the Vin Sequence after F it should be F and some numbers to the end of it and I'll check if this harness is the right one for ya

problem solved.
 

Thank you for the offer on the wiring harness; maybe another day (although I hope not).

It turns out it was neither the alternator nor the harness -- it was the ignition coil.

Again, in case anyone is interested, the symptoms were rough idling, with a very pronounced vibration, followed a day or two later with the engine dying with electrical power remaining.

A new ignition coil cured it all.

Congrats! Glad you figured it out!

Doesn't add up. Your car has three ignition coils, each of which fires two cylinders. Failure of one ignition coil causes two cylinders to stop firing, but the engine continues to run - quite badly. If the engine completely stopped, you've got another problem - possibly intermittent - that hasn't yet been identified and remedied.

Sooner or later it's going to be the wiring harness. It has the main harness and another called the Battery aka "B" harness, The "B" harness connects to the solenoid on the starter. If you're good at DIY, your can rewire the B Harness. The actuator aka throttle body also has he same wiring problem. Heat destroys the insulation in the harness. Therefore, the more the wiring is disturbed the more likely the insulation will fail and a short will occur.

"Limp Home Mode" is the tell tale sign.

A bad wiring harness can cause pronounced limping, but not the limp home mode.

Wiring Harness
 

At what year did the wiring harnesses become an issue on the W124?

I am looking at buying a clean 1990 300E and was wondering if the problem goes that far back in the W124 history. Thanks.

It does not go that far back. Problem starts in the 1993 model year with the switch from the m103 to the m104 engine.

Think about early M104s
 

The early M104 had the KE Jetronic injection with separate ignition. These had no harness issues. My guess is that late 1992 was the changeover point for the biodegradable harness.

I am in Europe so the US market might differ.

RayH

When was it fixed then?
 

Then, does the issue go all the way to the 1997 model with 6 cylinder 3.2L, or did they fix the wire issues by then? Thanks.

In the US we never had an engine choice - the sedans and T-sedans were m103 through the '92 model year and m104 from the '93 through '95 model year. (RWD only, 4matic cars retained the m103.) USA coupes received the KE m104 several years earlier, then updated (?) to the LH m104 at the same time as the sedans. So in the USA at least, it's a clear delineation based on model year. I imagine it is less so in other markets, where the sedan/wagon could be had with either the m103 or m104.

To the best of my knowledge, this problem does not exist on the 210 chassis cars.

Well, good call that there was more to it than the ignition coil. Like you said, the engine ran very poorly, unbalanced with the missing cylinders, before it stalled.

The Mercedes dealership replaced the ignition coils and it ran again, smoothly, until it stalled again a few days later. Mercedes towed it back in.

This time they say it's the crankshaft position sensor.

So it's still a bit of a mystery to me.