Strange Coil Pack/Harness Issues
 

This forum is almost dead so I’m not sure if I’ll get any light on this but figured why not try. Turbo swapped LSJ.

Last year I went to start my car in my garage and it ran on 3 cylinders. Pull the plugs and #4 cylinder is black. So I put in a new plug, no dice. Tried swapping with a set of spare coils/harness I had. Still ran on 3 but I’m pretty sure the cylinder was just loaded up. Because I then changed the one injector thinking it was sticking but it fouled the spark plug again after about 2 weeks of driving.

Season came to an end. This year I threw in my other set of coil packs/harness again. Lasted 2 months of daily driving. Car has actually never run better in my opinion. So ok something was clearly up with the old coils/harness. Well the other day same thing happened again. Went to start it in the garage and it ran on 3 cylinders. Checked and sure enough #4 cylinder was fouled again.

I took a “good” coil from my original car harness from last year and put it on #4. Still ran on 3 cylinders. Then for shits I grabbed my original harness/coils from last year and put a “good” coil on #4 from the harness I just pulled. Now it runs fine......

Yet this harness was doing the same thing last year other than the switched coil on #4.

I just don’t get it. But confused in what’s failing, confused what I’m doing fixes it and why it keeps happening. Figured I’d ask if anyone ever had the same issues.

Have you done a compression test lately just to verify that cylinder isn't down on compression? You could have something else causing your spark plug to foul though your first paragraph suggests is not the cause because you installed a new plug and it didn't help. I personally have experienced a single cylinder misfire that was actually caused by bad valve stem seal that allowed to leak through and caused the single spark plug to foul which would quickly cause misfires on startup. I'm not positive if the fouling was the only cause of single cylinder startup misfires (oil may have been saturating the plug after the car sat as well) but it would start properly for a while after installing a fresh spark plug though ultimately always ended up fouled and causing misfires on startup. Also, the car would eventually start to fire on the misfiring cylinder after it had ran for sufficient time though the elapsed time got longer and longer until the plug was fouled enough that the car would misfire under load.

If you are switching your harnesses, and switching coils, but the problem still comes and goes regardless of which coils or harness you have in there, the only other thing I could think is that maybe you have a bad connection where your coil harness plugs into your main harness, specifically on the main engine harness side of things. Next time it misfires you could try wiggling or disconnecting and reconnecting that connection to see if anything changes or you could find which wire specifically is the trigger wire for cylinder 4 and see if it is getting a signal on both the engine and coil side of the harness.

Compression is good. #4 cylinder actually had the 3rd highest out of the 4 cylinders. But all are close to each other. I was thinking valve stem seal myself. So when I started it up for the season I kept an eye on the exhaust. It should have puffed some smoke on fire up from sitting but nothing. The plug looks like soot not oil which leads me to too much fuel or not burning it well. But switching harnesses and packs around narrowed that down. It’s just so strange!

Next time it acts up I’ll start playing with connectors as you said. Thanks for the reply.

Might be worth looking at your injector harness and injectors. Could be a bad wire in the harness and moved things to swap coils.

Injector was changed but the injector harness isn’t something I’ve looked at actually. Thanks for the simple outside the box insight.