190E M103 eating ignition coils
 

Hello,

I made a post a couple of weeks ago about my car having twitchy tachometer and the problem turned out to be my ignition coil.

http://www.peachparts.com/shopforum/tech-help/289426-m103-190e-twitching-idle-error-code-29-a.html

I replaced it with a good spare (but used) ignition coil and after about 2 weeks of good use, I am having the same exact problems again.

I have a feeling something is destroying my ignition coil. how should I diagnose this?

My friends ML was eating coils when the voltage regulator in the alternator was bad. The voltage was slightly too high and it was rapidly killing coils. Ultimately he replaced the whole alternator but you can probably get away with just a regulator if your voltage is wrong.

Put a multimeter on your battery while the car is running and see what your idle voltage is.

I will do this, thanks DieselPaul.

It is strange because I replaced my voltage regulator around May of 2010.

What would be considered too high? >14.0V? >16.0V? If it is too high wouldn't my OVP kick in and cause the ECU/ABS to throw instrument cluster lights?

my voltage varies from 13.5-14.2v, I have a 143a alt

Most cars idle around 14v. North of 14.4 is worth talking about.

If the car is still running, then the ignition coil is doing it's job, i.e. creating a spark. My best guess is that you have a corroded wire or ground somewhere. Just a little bit of green stuff on a wire will cause all kinds of gremlins. Put that in the ignition circuit and the am radio probably has a bit of whine to it.

Oh PS:

Corrosion on the wires going to the alternator, OR the battery WILL cause your alternator to output a HIGHER Voltage.

Coils can function at a higher voltage. And they can wear out faster at that voltage.

I woke up early this morning to run some tests on the car.

Idling voltage with assumed bad ignition coil is 14.1V.

I checked all spark plug wire resistances and they were all within 1000Kohm - 1100Kohm range.

I also checked resistance across ignition coil. The 10mm and 8mm had 0.5ohms of resistance and 8mm to ignition lead wire had around 9Kohms of resistance.

I also checked the resistance of the 4 pole EZL plug. They were all within 1V of battery voltage (12.2V). Terminals 15 and 31 had 11.9V and terminals 16 and 31 had 11.88V.

I ended up swapping the ignition coil from my running 300E and started up the 190E just fine. It idled for about 10 mins and engine got warm. I shut it off and went to start the 300E which fired up without a problem with the presumably bad ignition coil (even drove it to work 30 mins away). When I went back to try to start the 190E, it would not turn over anymore.

So problem is not ignition coil anymore, perhaps the crankshaft position sensor? Strange because I replaced the CPS about 3 years ago when I was having cranking problems: http://www.peachparts.com/shopforum/tech-help/239318-m103-stalling-issue-fuel-mixture-cat.html

I will test the resistance of the wire when I return home.

I'm sure you meant 1K Ohms. Or did you actually measure 1 million ohms?

yes sorry, one thousand ohms.

i think i fixed the problem, I feel kind of silly.

I believe what happened was that my first ignition coil was legitimately bad. I replaced with a spare coil from a 400E which was only installable if the wires were bent in a funny way since the terminals were on the opposite side. I must not have tightened one of the wires properly causing the screws to loosen over a period of driving for 2 weeks.

I ran a bunch of ignition system tests on the car and they all checked out. I finally came to the conclusion that the wires to the ignition coil were bad. I had someone start the car for me while I jiggled all the wires and finally the car started. I loosened up all the bolts, reorganized the wires and retorqued them. Now the car starts fine and seems to run alright.

John, the diagnosis would have been much easier for us members if you mentioned in the first post that the second coil was not a direct replacement, and that you jerry-rigged it so the engine would run.

Recommend you buy the correct coil and avoid future problems due to overstressing the connecting wires.

Not to start another resistor spark plug "discussion", but was one of the major arguments for not using resistor plugs that they cause higher initial voltage on the coil secondary wiring, and could lead to reduced coil life?
Just a thought, but what kind of plugs are you running?

DG

coil & resister plugs
 

the Beru 4 plugs in my 103 seem to work very ell indeed though these are resister ones they do have a lower resistence comparable to Bosch plugs .the main difference could be that this is a Euro engine .
regards
mak