99 l67 swap sputtering under wot and over 3800 rpms (Page 3/3) 2002z28ssconv OCT 20, 11:33 PM Sounds familiar with what I used to get so here's what my issue was. But to be clear, diagnosis should always find a problem prior to random part replacement. If your coils are relocated and no longer on the engine, make sure they have a dedicated ground running to the ICM wherever they're mounted. I relocated mine to the firewall and it would puke all over itself as soon as I got above about 1 pound of boost. I was also burning occasional spark plug wires, like they were fuses. Running a new ground resolved everything.