im sure this is an old topic but ive got the dreaded random misfire code. compression is 200psi on all cylinders and there are no broken valve springs, i'll pulled the covers for a look see. fuel trim on bank 1 is higher than bank 2. bank 1 is +13 bank 2 is around +3. the unburned fuel smell well melt your eyes. when you first start the engine it does fine for a few minutes the you can feel the misfire start, then the code with flashing check engine light. timing light indicates all coils are firing, noid lights show each injector is being pulsed, you can hear them firing if you stick a screwdriver to them. also put in all new oem ac delco sparkplugs...so, O2 sensor maybe? anybody been there on this issue?

 

Most likely, it's a loose spark plug wire but also check the coil pack grounds at the rear of the driver's side head. It has been known to come loose.

 

hopefully. on my way to pick up a Snap-on Modis now to try and pinpoint this issue. nothing like having friends in the business to get diganostic tools like this for ya. fingers crossed.....

 

#5 coil bad....good thing for diagnostic scan tools.....

 

Good to see you found the problem.