About a month ago, on a cool morning I noticed a rough idle develop. I didn't pay it much attention, thought it would clear up, but after a couple days it did not. No CEL at all. I run a scanner on it after letting it idle a while and it had a P303 Code for a Cylinder 3 Misfire Pending. I read it again a day later, no codes. I have read it multiple times and sometimes it shows a P303 Pending, but no CEL. Usually it goes away, but the rough idle remains. A little more diagnostic after seeing the P303, I Pulled the Wiring that feeds each coil pack off and noticed no change in the engine when removing cylinder 3 wiring harness. All other cylinder firing checks caused the engine to change, but not on 3. I checked for spark by removing the plug wire from the plug and the coil pack was providing spark because it was arching without the plug connected. I replaced the spark plug.(They had been changed at about 110,000) But I replaced that one plug, no change. I moved the plug wire, no change. I thought I would just change the coil pack, no change. So by now Im thinking injector. I remove the intake and decide to replace all 8 Injectors. They were filthy. Replaced the injectors to spec and put everything back together and still same issue no change. I did all I knew to do, so I took it to a reputable shop. They put a nice scanner that they can see live data and on idle only cylinder 3 misfiring, when accelerating the misfire counts go down, seem to go away. They did a compression test, and is has 210PSI. And it passes a Leak Down test. Value Cover was removed and all lifter/rocker arms moving. They inspect the cylinder with a scope/camera and didn't find anything odd. Their diagnosis is that the Cam may have a place worn on that cylinder and they recommended a cam and lifter replacement or they leaned heavily to replacing the engine. The rough idle is not a steady rough idle, it shakes the inside cab of the truck, kind of levels out and shakes again, and repeats. I am just wanting to see what some of you guys that are smarter than me have to say. I have researched this, know about the AFM issues, I lean toward that myself. I used a OBD AFM Delete Tool about 60K ago, so I have been running on all 8 for a while. And yes it rough idles, with or without the AFM Delete Tool. But as I lean toward engine repair or replacement, something tells me this may be more electrical or sensor related somewhere. I do understand that most sensors would affect all cylinders and not just the one. Please help!!! And thanks in advance!!!!
Scott
