I have a 2001 z71 with about 72k miles on it, and it is running like crap. I hooked up a scanner tool and it said misfire #7. So I took out the plug and it was wasted, so I replaced it. It still runs like crap. Then I thought it might be the coil pack, so i replaced it with one from a 2005 8.1l engine and I still have the problem. What else could it be? I have read the other post in this forum but now I confused as to what my problem might be. Thanks for the help in advance!!!

 

What did the old plug look like???
Any thing done to the truck performance wise?

 

Truck has a catback exhuast and a hypertech programer. The plug looked like it was running to rich. The plugs are the stock ones. But I did replace them already. Also would the coil pack from the 8.1l be the same as the 5.3 ? They looked the same to me? Thanks for the help!!!

 

Try moving the injectors around. and see if the missfire moves too.
#7 is the lean cylinder, if the plug was just black and had no damage (usally caused by a brokin ring land) it should be a easy fix.
I'm unsure about the injector coil you could alwas swap number 7 with a different cylinder and see if it changes anything. but just do one at a time. (Inject, coil pac, plug, wire)
BTW, when does it miss fire??

 

Misfires all the time even at idle. It runs really rough especially at idle.

 

Check all plugs for the injector and coil pack. try swaping out the #7 coil pack with #1, then try swaping out #7 injector with #1. Also make sure the plug wire is not brokin so maybe swap that too, if it still miss fires after you have ruled out the coil pack plug wire and injector, do a compression test, you may have bigger problems.

 

That dirty #7 !

 

I had the same issue and chased it for days. Ended up being the wiring harness. Where the harness connects to the injector, the metal clips were loose and not getting a solid connection to the injector itself. I squeezed the inside of the clips together and slid it back on the injector and the misfire was gone.

 

Up-date on this?