Engine Missing problems
 

Hi everyone!

I just signed up to the forum and this is my first posting. Hope y'all can help!

On my 94 C280, which I bought just two months ago, I am having some intermittent engine missing problems. I think they may be related to the wiring harness, maybe. The car has 100K miles, and it looks new all over, but I have no maintenance records from 70k to now. For prior history I just have the MB service book.

Basically, this has happened on two ocassions once yesterday, once the day before: After driving for about one hour in rainy conditions, the engine starts to miss badly, both at hi speed/rpm and at low/idle. It didn't completely die when at a stop light, but it sure felt like it was going to. When accelerating from a stop it was very sluggish. It did make it home, though. This morning it ran fine all during my 80 mile commute to work. I just hope the problem does not reappear before I can look into it this weekend...

I haven't started to troubleshoot it yet, but I will start by checking spark plugs and wires. After that, what would you suggest?

Thanks in Advance!!!

It could be your engine wiring harness, but I'd go to any Mercedes dealer to see if there is a record of its replacement in the system. Have a dealer run a VMI (vehicle master inquiry), which shows a record of all warranty / recall work done on the car. You can also check the harness yourself if you feel comfortable doing that.

Another likely suspect is a bad connection between the resistor boot and the coil wire. These engines use non-resistor plugs like old VW's and Porsche's. The resistance is in the boot or coil wire end. It basically connects the coil wire to the spark plug. Your engine, like other M104 engines, doesn't use spark plug wires and a distributor. It uses a "coil pack", and three coil wires which connect directly to three spark plugs, and piggy-backs to the next spark plug via a high tension lead. The coil wires rarely, if ever, go out. The spark plugs are to be replaced every 30,000 miles. Whenever there is a miss problem, the most common culprit is the resistor boot.

Last, the Mass Air Meter and / or throttle actuator can cause similar problems.

Yesterday I had no repeat of the problem at all, during my 160m daily commute... I hate this intermittent malfunctions!

Thanks for your suggestions, Suginami. I will try to look into it this week end and post my findings later.