Goodbye vacuum leak, hello misfires!

When I purchased my car in 2011, it had 11k miles on it. The only mods done to it at that point were the JCW intake and Borla exhaust. I had to assume these were done by the dealer, seems pretty likely, but had no way to verify. I rarely had any engine codes pop up in the 60k miles I've put on it since. Last month I swapped out the supercharger pulley for a 15% Alta, and bumped the injectors up to 380cc. After chasing a vacuum leak down for a couple of weeks everything was fine and dandy. This weekend I got a P0301 - misfire in cylinder 1. I pulled the plugs, which had less than a few weeks of driving on them, and they were all sooted up pretty heavily. I was able to clean them up so they weren't fried (yet), but I am wondering if that will be next based on what I am seeing now.This car is my daily driver, not planning on tracking it at all. Should I swap the plugs back to the OEM ones? I read something about the colder plugs being most useful for the track but not for daily driving. If that is not even a worthwhile test (plugs are cheap relative to the rest) I guess I'll get to learn about compression tests next.

15% Alta Supercharger Pulley
380cc Fuel Injectors
NGK spark plugs (1 step colder)
JCW intake flap locked open

 

Check fuel pressure. And weak spark will also effect plugs.

 

Swap spark plugs around and see if the fault repeats or follows the spark plug, if it follows the plug replace it, if it stays with the cylinder than chances are it is your wires or coil ... cheapest test is swapping wires and repeat, does the fault follow the wire or does it stay with the cylinder if it is the wire replace them, if it stays with the cylinder then chances are you have a failing/cracked coil pack.

Best of luck.

Motor On!

 

I will give all of that a try tonight. I appear to be running lean as well, so maybe I'll shut that JCW intake flap for the time being.

 

Smoke test it yet ? I found a great write up here on how to do it on this car..pretty easy too.
Check coil pack terminals for corrosion or the inside of the plug boots seating well onto the sparkplugs ??

 

I cleared the code and have been monitoring STFT & LTFT, along with a few other things, while driving around. Everything seems to have smoothed out but I am going to pull all the plugs and the coil pack this weekend to see how it all looks. Fuel trims have been 0% to -10% range since yesterday for most of the time at idle and steady driving. Looking through some of the numbers I was running pretty lean for a while there when that misfire code showed up, so hopefully this puts me in a better spot. My car always ran a little rich before the pulley and 380cc injector swap, so hitting lean at all surprised me.

 

Figured I'd come back to this thread and add a picture of both my O2 sensors I just pulled out. I think they may have been victims of my rich fuel problem...

Looking forward to getting my WMW-tuned ECU in the car and everything buttoned back up for some test driving!