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Was no issues. Changed plugs bc old ones looks horrific, did New plugs, P0302, did coils, no change, did injectors and pcv valve, nothing, mechanic said I could have gotten faulty parts. He changed them. Now he’s saying it only misfires until car reaches temp, he said ecu is turning off coils, he has 1 more test then he’s calling it a bad valve. Thoughts?
Wouldn't be the first pentastar engine I seen with a bad valve, or roller follower, or camshaft...
If there really was no performance issue what so ever and you just decided it would be fun to do plugs, then I guess you could have disturbed the upper intake manifold seals (it's possible for that to cause cold running only misfires) or maybe even something fell in the open intake.
Hard to say without some test results. Let us know what your mechanic finds.
Before going after valve, I would check for vacuum leak. If you did not have a bad valve before changing the plugs and injectors, you are not going to have a bad valve after the change.
Here is the official report and diagnosis. Let’s hear what anyone has to dayzVerified customers concern with active misfire data on cylinder 1 and 2. Pulled upper intake manifold and found the lower intake manifold front bolt to be stripped, Removed coil and spark plug from cylinder 1,2 and swapped them to cylinder 3,4. Replaced lower intake manifold and re assembled the upper intake. The misfire did not follow. Remove upper intake manifold, moved 1,2 injector to 3,4 cylinder. Reinstalled upper intake manifold. Misfire once again did not follow. Did see a slight screen issue on cylinder 5 injector replaced it due to unforeseen potential failure.
From this point on a cylinder compression test was performed to see if we seen a issue with a potential failed camshaft or roller. cyl1 148, cyy2 145, cyl3 145 cyl4 145, cyl5 150, cyl 6 150. All within reason and specs.
Pulled upper intake manifold again, Pulled both cylinder head valve covers to visually inspect all 4 camshafts, and all rockers. No issues present. Traced all wiring for coil packs, injectors and checks fuse box and ECM for any corrosion, All wiring inspections and test came back with no issues Present.
Put engine Back together and do a crank relearn along with adaptive reset. Issue still present. Issue does happen violently upon cold start and sometimes does not read misfire data all though misfire is present. Miss fire does go away slightly if not all the way after vehicle is warmed up. Leading to the current diagnoses of a bad valve seat/seats/valve or valves on cylinder heads. From past experience a cylinder leak down test will not show a bad valve seat. Previous years of the 3.6 had left cylinder head recalls for this failure as described. Advised customer of issue and the cost to fix. Will be taking it back to the dealer he purchased vehicle from.
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