Hi everyone,
I recently bought a 2004 GM ultimate edition and everything was fine. I left it sit for 12 days while I was on vacation and when I came home and started it the engine light was on and it was running rough. I grabbed my code reader and it said secondary ignition fault ( I forget the code number but it was the code for cylinder 6). I put new coil packs and spark plugs on it today but that didn’t solve the problem. It only does it intermittently and sometimes it does it worse than other times and sometimes not at all. Whenever it is running rough the ac compressor clutch kicks out also. Anyone have any ideas? Thanks

 

Since it started misfiring after it sat for 12 days, you might want to look for rodent chomp marks on the wiring which might be shorting.