[xer]

7 days ago started up the truck and have a knocking noise from the engine. I have read all the post I could relate to my problem and have done the following, replace fuel filter, checked for harness rub at the alternator, doulble up on the hot shot additive for a full tank, no cure. I run a normal dose of hot shot every tank, I have replaced number 2 and 7 injector plug with gm replacements a couple of years ago. I also put back to stock mode, I run the tow mode usually on my Ppe tuner. The local dealership is not know for their service department so I took it to a local shop to check for any codes. Oh check engine light have never came on. The shop said I had a misfire on #8 cylinder. I notice that several post has said to only use the tech 2 scanner but I notice they use a snap on brand. Does this really matter? I got home and shook the plug on #8 while it was idling and did not make a difference in the knocking. Is it possible it could be the ficm and is there a way to check it, or is it a bad injector. The truck has 195000 miles and I am the original owner

Thanks in advance