[madvmax]

My 1994 420 S runs great when cold but has a mis when warm.I replaced plugs and am thinking of rotors and caps next any ideas?

 

[samosali]

maybe it is not a mechanical problem. I have similar problem and after 6 years there is no improvement after replacing almost everything which can be replaced under the hood. now I am researching signals between computers and ignition control module. I hope it is wiring.

 

[nowhereman]

Consider the EZL. (Ignition control module). The power transistors slowly wear out and they show bad behaviour when hot.

 

[MAVA]

Like Trevor said it is the Ignition Module, but along the way of the ignition module. The white thermal compound must be replaced, yet the old stuff must be cleaned-off entirely. The dried paste could be your problem

A medium to a large size tubes can purchased at electronic supply houses, or you could find them on FleaBay, but the ebay ones from China are too watery, and are prone to drying up rapidly. The stuff from the US never dries-up and it is thick...

The paste is never lathered on. The paste is there to promote thermal conductivity, and too much it works as a thermal isolator. The application of the paste should be on both surfaces, and it should look semi-transparent. It is there to fill the metal mating imperfections..

Get two to three tubes of this stuff:

New Aavid Thermalcote 249 Thermal Joint Compound CPU Heat Sink Paste 28g 1oz | eBay

Martin

 

[samosali]

Consider the EZL. (Ignition control module). The power transistors slowly wear out and they show bad behaviour when hot.

yes of course. consider it.

BUT you cannot count on it. It would be too easy. like i said, by this logic i replaced almost everything what it can be replaced under the hood. Only because it sounded plausable and somebody (or myself) gave me an idea what it might be.

Wrong. i still do not know how stupid i was to act like i did. I will not write the number in dollars which i put in 20 years old car. But it was for sure at least 20 times more than oscilloscope from china which costs 220 EUR. once you will get it (couple od days after purchasing on ebay for instance) you can measure practically everything related to your engine management computer(s) and EZL. EZL costs about 3000 EUR here in europe. Remanufactured or used ones are ca 700 EUR. Still 3 times more than oscilloscope. You can masure signals which come into and out of EZL in one afternoon ! if you are not familiar with measuring techniques you have two options: learn them and secondly, prepare yourself to be MAYBE disapointed every time when somebody will give you an idea what might be wrong with your idle. by the way, rough idle is a terrible thing to diagnose.

one more thing: i was told that bosch EZLs are prone to fail due to age much faster and more frequently than Siemens ones. i was 99% sure that my ezl is bad and after replacing it with tested one from germany you should see my face; idle was exactly the same.

 

[86560sel]

Thermal compound eh? I wonder if that is what my warm miss problem could be? I replaced the EZL with a used one that Trevor kindly sent to me, but I still have a warm miss. This car about has me to the point where I am going to rip my hair out. I cannot replace the rotors because I stripped out one of the screws. Still trying to figure out what I am going to have to do there.

To the OP - good luck, hopefully you will not have as difficult time as I have had to get a good running W140.

Like Trevor said it is the Ignition Module, but along the way of the ignition module. The white thermal compound must be replaced, yet the old stuff must be cleaned-off entirely. The dried paste could be your problem

A medium to a large size tubes can purchased at electronic supply houses, or you could find them on FleaBay, but the ebay ones from China are too watery, and are prone to drying up rapidly. The stuff from the US never dries-up and it is thick...

The paste is never lathered on. The paste is there to promote thermal conductivity, and too much it works as a thermal isolator. The application of the paste should be on both surfaces, and it should look semi-transparent. It is there to fill the metal mating imperfections..

Get two to three tubes of this stuff:

New Aavid Thermalcote 249 Thermal Joint Compound CPU Heat Sink Paste 28g 1oz | eBay

Martin

 

[Joflewbyu2]

Miss? Which cyl? If you can track that down, you will know which cap and rotor, plug or plug wire needs attention. Hows your catalytic converter? Tap them with a rubber mallet. Hear any material loose and moving?