I have a 98 z28. Just put on a ls6 intake and removed the EGR and AIR. Have not had the chance to have the codes removed. After I put everything back together it began to misfire really bad, at idle and when I gave it some throttle, in cylinders #5 and #7. I then took it all back apart to make sure I didn't pinch a wire and make sure I plugged everything in.
Things i have done.
Changed wires and plugs, checked compression(it was good), and fuel pressure (it was good). Then swapped around the injectors and coil packs and the misfires still remained in #5 and #7 cylinders. All vacuum lines are plugged in and were inspected upon installation.
Car has a cam and LT headers with a cat delete. Only other thing I can think of is that it desperately needs a tune, but I didn't think the intake would make that big of a differance. I have no idea where to go from and the car has been down for almost three weeks. Any help would be appreciated.

 

Is it possible that your driver's side coil pack harness has been reversed?
If it was removed, & then reinstalled "backward", then spark would now be supplied 7, 5, 3, 1, instead of 1, 3, 5, 7.
If you think it might be, verify the color code on the harness...
#1 blk/brn/ppl/pnk. #3 blk/brn/lt blu/pnk. #5 blk/brn/dk grn/pnk. #7 blk/brn/red/pnk.

 

I looked but it was all wired correctly. Thanks