6.0 LQ4 rough idle, misfires

My buddy swapped an 04 LQ4 into his 00 Sierra about three weeks ago. The last few days, it has began to misfire. We assumed its either an injector, coil pack, spark plug or wire because its only two cylinders misfiring. after swapping coils, plugs, wires, and the injectors, the truck still continues to misfire. note that the misfire is only on cylinder 1 and 5. he had the truck hooked up to a machine and none of the other cylinders were misfiring. the number 1 cylinder fluctuated from 5 misfires to 16 misfires. what would you suggest he do next? is it a possibility that its a tuning problem since he's replaced the 'mechanical' parts? thanks in advance!

Has the PCM been retuned for the additional displacement? It could be lean and the spark plugs are burned up.

<div class='quotetop'>QUOTE(RedHeartbeat &#064; Apr 15 2007, 07&#58;12 PM) [snapback]90024[/snapback]</div>

Quote:

---

Has the PCM been retuned for the additional displacement? It could be lean and the spark plugs are burned up.
[/b]

---

Yeah, it has been retuned. Like I said, its not all of the cylinders misfiring. It&#39;s only the first and fifth cylinders that show misfires. Plugs, wires, coil packs, and injectors have been replaced on both cylinders. We&#39;re not sure what else it could be.

vacuum leak? haha

spray some carb cleaner or water or penetrating fluid etc etc on the intake manifold especially if you have ran nitrous through it. A couple of my buddies and my old 4.8 as well cracked and or lost the intake manifold gaskets and caused the exact problem you are havin. just a suggestion

i am actually having the same problems with my ruck, but its a 5.3. yeah I did the compression everything is fine, but it&#39;s on the low side of power ( i lose to my friends v6 dakota) Pretty bad...i did the water spray test and spayed water on the exhaust manifold and those two took longer to evaporate telling me no hot gasses not firing, plus i took it to extreme performance here in phoenix specializing in that block style (mostly corvettes with the ls1&#39;s and stuff) and the hooked it to there computer and it reads a misfire almost every rotation on those...and i have all kinds of codes which is normal w/ a cam but some i dont think are like the injector trouble code, idk im STILL didn&#39;t get my tuner but im hopeing that will fix it, maybe?

Be sure to check all the grounds to be sure they&#39;re tight. It&#39;s easy to miss one when swapping engines since they&#39;re all hidden behind the driver&#39;s side cylinder head.