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Got a misfire on #4 on a 08 yukon 5.3. 200k+. Its a friends. broken timing chain tensioner. replaced with ls2 style. new chain. new oil pump and o-ring. cleaned the plastic from the pick up tube. replaced cam sensor. also had some emissions codes. replaced the purge valve and solenoid. that took care of those codes. But cant get rid of the #4 misfire. switched coils, plugs and wires with another cylinder. Problem still there. switched injectors. No change. removed valve cover and rotated engine to make sure I didnt have a stuck lifter. All rocker arms are moving. Did a relearn procedure with HP tuners. Nothing is working. Anything else I could look at. I was going to try intake gaskets and grounds. I was thinking of using some jumper cables as a temporary ground to see if it makes a change. Any ideas please
I did a compression check. #4 is very low. Added oil to the cylinder. Checked again. Nothing changed. Pulled head. Nothing obvious. Pushrods straight. Lifters appear ok. Ill remove the springs next. Here's a pic. The exhaust valve is grey while the others are white ish. What do you think
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Po 304 problem 
