Bad spark plug

jkcrewsn · jkcrewsn's Garage

I went to pick up my car yesterday after the torsion bar work and the guy asked me if it always ran like crap. Although I don't have a benchmark to go by, I told him that sometimes it runs kinda rough and it feels as though there is a slight miss when deep into the boost in second or third. Well, he proceeds to tell me it sounds as though it was running on five cylinders. I told him I didn't think it ran THAT bad. Well, sure enough, I drove around the block, and it was running like crap. So we pulled the plug wires one by one while it was running and sure enough, number six wasn't firing. Pulled the plug and started it, it wasn't arcing. So put another spark plug in, started, and it arced. Replaced the plug and now it is running on all six. Has anyone ever heard of a plug going bad? All he did was replace the torsion bars and bushings, nothing mechanical. He said it was the first time he had seen it, and he's been wreching on Porsche's and BMW's for almost twenty years. I could see if maybe it was out and got dropped, but not just up and quit.

Rick Lee · Rick Lee's Garage

Exact same thing happened in my '87 BMW 325is. Wrench said it meant all kinds of problems and to start looking for another car. That was 100,000 miles ago and it runs better than ever. No explanation - just gremlins.

stlrj · 05-02-2002, 09:24 AM

Plugs going bad seem all too common particularly on 911's with stock ignition cables.

It appears that there are too many unnecessary connections that are susceptible to failure to cause a plug to eventually fail suddenly without warning.

Cheers,

Joe

Superman · 05-02-2002, 09:44 AM

I recently had some fouled plugs (not on the 911) that would make sparks outside the combustion chamber (like laying on the valve cover), but would not make a spark under compression. Obviously, the engine simply would not even begin to start. Changed those four plugs and it started easily. Yeah, I'd say spark plugs are important.

Jim Sims · 05-02-2002, 12:31 PM

Was the plug oil fouled? Jim

jkcrewsn · jkcrewsn's Garage

I am not sure what it would look like if it was fouled, but since it wasn't firing, it was completely black and looked wet. We pulled one of the other plugs to compare with, and it was mostly black (wrench said it is running rich), but it was grey/brown where it was sparking.
By the way, I am running 10mm Magnecor wires w/ an MSD 6AL ign.

Jim Sims · 05-02-2002, 12:46 PM

If the "wet" evaporates it's gasoline, if not it's likely oil. Oil is not good. Running rich can be cured by adjustment. Oil can mean other problems - valve guides, rings, etc. Jim