I just had my 2003 Silverado 1500 5.3 4L60e sent in for a rear main and oil pan gasket reseal as they were leaking. I also said screw it and had the knock sensors replaced as the GMT 800s are known to have corrosion. I also had the valley pan gasket replaced. Mind you, the truck ran perfectly before all these repairs from my local mechanic. After the repairs, my mechanic told me the truck was misfiring. He recommended to have the spark plugs changed, so I obliged. He also changed out the O2 sensors and said that was the issue. Well, I get home and turn my truck on to hear a fine idle then a few seconds later I start hearing vibration. As soon as I go out and listen to my exhaust, I can hear the misfires. I do not understand what to do. I do not know how to tackle this. I do not have an OBD2 that shows what cylinders are misfiring. I just have an Innova 3160RS. Anyone have any suggestions? I’m thinking maybe look at MAF?
So I had the same issue with my 06 Blazer. I was too late to fix it, so it started knocking, but what I did was change the spark plugs, and it didn’t change anything, so I went to the coil packs. If you got the tools and it’s still misfiring, check the coil packs and see which one is faulty if there is one. I’m not mechanically smart, but I’ve had this issue.
Also, don’t forget to check the wiring to the coils. Sometimes a loose connection can cause misfires.
You might want to check the MAF sensor too. If it’s dirty or malfunctioning, it can cause misfires as well. Just make sure to clean it with the right cleaner.