P0303 Misfire code on 2008 Yukon XL 6.2L Denali. Part Swap didn't fix
What is your question?
Swapped plugs, coil packs, plug wires, fuel injectors and even the entire coil pack assembly (drivers side to passengers side and vice versa) and still sets P0303 code and stabilitrak messages/codes. Code always stays with Cylinder 3. I don't have a bore scope to inspect the bore and I'm going to buy a compression tester tonight to check compression on all cylinders. If there ins't evidence of a mechanical issue (rings, burned exhaust valve or burned intake valve preventing compression to build) then how do I track down the source of this issue. No obvious vacuum leaks or loose wires. Hard for me to diagnose a short in the electrical system without some tutoring on where to start. Can't afford to take the vehicle to a shop or dealer currently so I'm hoping for a DIY repair solution
What makes this problem better or worse?
Same rough idle regardless of what parts swaps I've done.
How long has your 2008 GMC Yukon XL 1500 had this problem?
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I was able to check cylinders 1, 3, 5., & 7 dry and wet before my compression gage stopped working. I’m going to replace it tomorrow morning and finish the other side.
Results from drivers side:
Cyl 1:
Dry 150 psi
Wet 165
Cyl 3:
Dry 145
Wet 165
Cyl 5:
Dry 160
Wet 175
Cyl 7:
Dry 145
Wet 155
The P0303 code remained consistent regardless of part swapping.
For additional clarification, I also pulled the drivers valve cover off And inspected valve springs & keepers were fully engaged. I removed both rocker arms from cylinder 3, removed both pushrods and rolled them on a flat surface to ensure they were straight and not bent which they were not.
On more thing worth mentioning. I’m still getting P0303 and when that code is triggered, the message center always flashes service traction control at the same time. Not sure how/why but it does.
I performed a Noid light check last night on Cyl 1, 3, 5 & 7 and its showed injectors were firing regularly on all those cylinders. I didn’t notice anything abnormal however that was my first time doing a noid test
I also purchased a spark tester and checked each cylinder. The only thing I noticed was cylinder 3 was weak compared to other cylinders and sometimes intermittent. Trying to determine why that is....how do I check for a grounding issue?
Let’s find out what it’s NOT.
I was able to check cylinders 1, 3, 5., & 7 dry and wet before my compression gage stopped working. I’m going to replace it tomorrow morning and finish the other side. Results from drivers side: Cyl 1: Dry 150 psi Wet 165 Cyl 3: Dry 145 Wet 165 Cyl 5: Dry 160 Wet 175 Cyl 7: Dry 145 Wet 155 The P0303 code remained consistent regardless of part swapping.
For additional clarification, I also pulled the drivers valve cover off And inspected valve springs & keepers were fully engaged. I removed both rocker arms from cylinder 3, removed both pushrods and rolled them on a flat surface to ensure they were straight and not bent which they were not.
Finished checking the rest of the cylinders. Results below. Cyl 2: Dry 175 Wet 185 Cyl 4: Dry 165 Wet 180 Cyl 6: Dry 160 Wet 175 Cyl 8: Dry 155 Wet 170 I’m looking for suggestions for next steps...
Spark plugs all looked consistent. Mainly white with a brown side on all plugs. Running AC Delco 41-110 plugs.
On more thing worth mentioning. I’m still getting P0303 and when that code is triggered, the message center always flashes service traction control at the same time. Not sure how/why but it does.
I performed a Noid light check last night on Cyl 1, 3, 5 & 7 and its showed injectors were firing regularly on all those cylinders. I didn’t notice anything abnormal however that was my first time doing a noid test
I also purchased a spark tester and checked each cylinder. The only thing I noticed was cylinder 3 was weak compared to other cylinders and sometimes intermittent. Trying to determine why that is....how do I check for a grounding issue?
I posted alot of results but haven’t received any feedback. Do I need to do anything else to glean feedback?