Cyl 1 and 4 misfire

**MyLittlePony** · 11-17-2015

Ok so this should be an easy thing to diagnose right?

Well, I have swapped coils and Cyl 1 and 4 still show misfires in the the Torq App, another interesting fact is that around town driving, stop and go, there are no misifres being detected, but if I am driving on the Interstate it starts misfiring.

Currently I have a 3.6 pulley, AL104's, 3" downpipe no cat, intake, ported blower. Again this only does this at high speeds, my initial thoughts is that since the rear O2 is tuned out and I plugged the O2 bung with an O2 bung cover (the bolt that comes in headers that have O2 bungs), that maybe it is the tune. I tried different coil packs and it still does it only on 1 and 4.

**04lss** · 11-17-2015

Check your plugs, I cracked one once and had similar results.

**ericspecullaas** · 11-17-2015

i would look deeper into it and im going to say you chipped both pistons

**Slick2500** · 11-17-2015

Originally Posted by ericspecullaas

i would look deeper into it and im going to say you chipped both pistons

My black 97 GTP had an issue like this, driving around town it was fine, but as soon as I got on the highway it would set the CEL for misfires. I replaced plugs, wires, harmonic balancer, injector orings, icm, coils, both o2 sensors, all the vac lines, the egr valve, crank position sensor, cam position sensor, and it still had misfires it actually got worse as I replaced things, went from a p0302 to a p0300. Finally decided one day to open it up and I found 2 chipped pistons.

**Fivefingerdeathpunch** · 11-17-2015

What plug gap?

**MyLittlePony** · 11-17-2015

I gapped em at .050" I was told .050-.055 is great for these cars, I knew I had a smaller pulley when I bought the car and decided to go with a closer gap to get a better burn, I know it's only .005" but it's my preference.

Funny thing too is that I put a scope in cyl 1 and there is a shiny side and I am really hoping it is not a chipped piston. Would there not be more symptoms?

**ericspecullaas** · 11-17-2015

you get a misfire on that piston and thats really it. if you see the spark plug all shiny then its chipped. the fact that its shiny now says it did chip once before

**MyLittlePony** · 11-18-2015

It would have chipped in the last 4 months, and I have to pull the plug, last time I checked I put a scope in the spark plug hole and one part was shiny, it could also have been a reflection of the light. I suppose I could pull the front head and see about getting one new head gasket. I'll just check into it some more and see if I can get a better video.