samtheman48

So, I'm new to the forum, and I found a very nice 1993 300e. It has 106,000 miles is in fantastic shape cosmetically, but it has a severe misfire. I'm not a stranger to working on German cars (as I have a BMW e30 from the mid 80s), but I'm not sure what to look for specifically on these cars. First, The lady, who is older, says she's had the car for three years, and in that time, she has done a bit of work on it. She said the misfire happened after she got the head gasket replaced. She said it was very slight and not very noticeable. When she had a mechanic look at it, he looked it over and said it needed a new ignition coil. He replaced it, and then it ran terribly. By this point the lady parked it, and bought a new car. So, I went to look at it today. It started right up, and ran-- but not too well. It mised at all rpms, but it didn't sound too good. When I took it out for a test drive, it had no power, and it shook quite badly. It started without hesitation, but once running, it sounded as if there were two cylinders mising. As I've said before, the car is in good condition otherwise. She wants $500 for it.
Tell me what you think.
Thanks

Shadow5501

It may very well be missing on two cylinders. This car uses three ignition coils, each of which fire two cylinders. (There is no distributor.) If the ECU detects a misfire it can shut down that cylinder pair.

Each ignition coils sits atop one plug, connected by a so-called "boot." It fires the 2nd plug via a conventional wire. The boots are known to fail with age and cause misfires. As well the coils and wires can go bad, but this seems to be less common.

Also, this engine hates platinum plugs. Use only the recommended copper plugs.

Not too bad, eh? However, there is a worse possibility. The main engine wiring harness on this engine is know to degrade. The insulation flakes off, causing short circuits and crossed signals. Most of them have been replaced by now with an updated part number. From your text it sounds as if the car ran worse after the coil replacement than it did before. This would seem to indicate that handling the wiring harness (to replace the coil) caused the insulation to fail. Makes me think it has the original harness. Ask the owner if the wiring has been replaced. They would remember the repair because it would have cost more than $1k.

The car sounds like a deal if it needs only plugs and wires. OTOH if it needs a wiring harness, it's a fair price but nothing special. These top out at not much more than $2K no matter the condition, and you would have that much (or more) into it by the time you got it running right.

I owned and maintained a 1993 300E 2.8 for more than 10 years.