95 E320 rough running
 

When I started the car yesterday, the engine suddenly developed a vibration. This vibration is with the engine at all speeds. I thought I was running on five cylinders. I tried to diagnose the problem by disconnecting each injector to find the missing cylinder, but this isn't the case. The engine runs rougher each time I disconnect an injector. What could be causing this vibration?

No check engine light came on. I went to read the codes, and interestingly, the #2 LED light was on, and there is no response to testing. Perhaps related?

Maybe weak spark from either bad wires or a bad coil. Was it a wet day for you yesterday? maybe try spraying some water over the wires and see what it does... Oh, also, sometimes the valve covers leak into the spark holes and fill the wires with oil. Pull up the coils and wires and check for oil puddles in top of the plugs.

i had this in my car..and replaced the 3 coil wires.... never had an issue again

That's what I thought - a bad coil. But why doesn't the dead cylinder present itself when I disconnect the injector?

Sometimes an engine vibration is just a bad motor mount.

Kestas, I had a similar problem with our 1995 E320. Turned out to be a bad coil pack. Bought a new coil pack and swapped it into the 3 different coil locations ... the rear coil pack was the bad one. If you find that the engine mounts are collapsed recommend buying replacements from a MB dealer because some aftermarket mounts are inferior quality and fail quickly.

I would think at all speeds would point away from motor mounts. I'd suspect the 16 pin problem may be related, in any case it's a good place to start so that you can read the codes. Wiring diagram for the data link connector is here - http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1995/E320/SYSTEM%20WIRING%20DIAGRAMS/ One thing that sticks out is that pin 16 power comes from the OVP relay.

I'll ignore my attempt at diagnostics and go ahead with new coil packs (and wires). It just makes too much sense to think it's anything else. At 107K all ignition parts are original. It won't be money wasted.

I'll be going with Bosch for the parts. Beck Arnley is a second choice. Other choices (cheaper) are Delphi, Bremi, and Prenco.

The OVP was updated long time ago. I should also mention the engine wiring harness was replaced nine years ago and shouldn't be an issue.

Fixed! I replaced all three coil packs, wires, and connectors. $240 later the problem is gone.

good feeling isn't it?

I didn't see any mention of you pulling codes. The $15 Radio Shack parts code tester is what I'm talking about.

If you'd have pulled the codes from the car, it would have told you WHICH of the three coil packs had gone bad. Not that replacing all 3 is a bad idea, but you can indeed pinpoint it down to the specific pair of cylinders that have the bad pack.

Cheers,
Gerry

I've had 4 separate instances of rough running that were corrected with a coil swap. In all 4 cases, no codes were present. Is it possible for a coil to be "weak" enough to cause run problems, but not weak enough to trip a fault code? Are there certain types of coil failures that don't trip fault codes?

As a side note, the coil to plug "boot" type connectors are also a known common failure item. They are cheap enough that I replace them any time I have run problems, change plugs, etc......

J. M. van Swaay