I have been using this site for a few years now but I just became a member because I have not found exactly what I need yet.

I have a 2001 L, aftermarket pulley on supercharger giving it 15 lbs of boost, SCT tune, aftermarket COP's, CAI, EGR delete. I am getting a code for cylinder 6 missfire, I have tried swapping the COP's and spark plugs around and the issue stays at cylinder 6. I have had a compression test done and it passed, the truck starts and runs good though, it still has quite a bit of power but its not all there. It does not backfire or anything like that, the last shop I took it to they wanted to rebuild the motor for a few grand and see if they could find the problem, I don't want to keep throwing parts at it hoping it fixes it. Any help is appreciated. Thanks.

 

Bad Injector?

 

I swapped them around too but cylinder 6 still misfires.

 

Try a one or two step hotter plug in that cylinder (if anyone makes one to fit it). You might also try increasing or decreasing the gap slightly to see if you can keep better ignition. I would not trust or use a shop that wanted me to completely rebuilt an engine simply because they couldn't find the source of the problem! Find someone that knows how to use a old fashioned vacuum gauge and also try using an old fashioned scope type ignition analyzer to see what's going on inside the engine. A vacuum gauge is good for finding mechanical issues like sticking or leaking valves and leaking head gaskets and an ignition analyzer will find spark, electrical and compression issues.

Since your engine is boosted, I'm not SURE that a vacuum gauge will show a pattern but I think it will. And note for everyone, diagnostic "vacuum" gauges usually show both vacuum and pressure readings so it should be usable on a boosted engine.

BTW how do the tips of the spark plugs look on this and the other cylinders? That will usually tell you if there is a problem and on which cylinder.

 

Good compression. Good spark plug. Good injector and it still misses. it either isn't getting spark or fuel. Have to check a little closer in those areas.

 

Exactly what ignition analyzers and vacuum gauges are good at.

FWIW I was thinking of your case last night and I remembered a problem that I had on a F.I. Nissan Maxima years ago. After routine maintenance at the stealership, it developed an occasional misfire. After a lot of troubleshooting I realized that if I pushed on the wire to one of the fuel injectors the engine would misfire slightly. I checked the connector on the fuel injector and I found that Goober, the stealership mechanic, had YANKED the connectors off by the wires and had broken the latch that was supposed to latch them to the FI connector. He's also lost the seal in several of the connectors. Long story short, this connector had gotten corroded and would fail to make contact if the cable flexed in a certain direction. The stealership wanted $1200 for a new wiring harness but I finally found an auto parts store that could order the connector parts and seals so was able to repair the harness. The misfire went away completely after that. Stories like this are exactly why I dislike mechanics that just want to start rebuilding the entire engine for non specific faults. Rebuilding would have NEVER fixed the problem that I had and I'm doubtful that it would fix your problem either.

PS story #2. The same Nissan Maxima used to have another occasional misfire and the computer reported that the distributor was bad. The stealership wanted $450 for a distributor and $400 to put it in (this in about 1986). These distributors are VERY simple compared to the old traditional distributors, all of the timing is done with optics instead of points, the timing advance is all done in the computer and the vacuum advance is also done in the computer, so I told them no and that I would troubleshoot it. I connected an oscilloscope to the distributor output and looked at it and there was NOTHING wrong with it. I finally noticed that the contacts for the high voltage inside of the distributor were burnt. It turns out that they were made of ****ty aluminium instead of the traditional brass and although the car only had about 25,000 miles, the distributor cap was TOAST! Replacing the cap and rotor (less than $10) immediately fixed the problem. This story is just another example of how many modern mechanics fail to do ANY trouble shooting and instead just want to start replacing expensive parts!

 

Are you sure you are looking at the right cylinder? #6 is 2nd from the front on the driver's side.

 

Yeah it is cylinder 6. Second from the front on the drivers side.