Hi all! Sorry for the wordy post. Short version is I have a #2 misfire and everything appears to be working properly, but suspect the thing is just worn out and needs rebuilding/replacing.
1997 GMC Sierra C1500
5.0 with 188k
Quick history:
Bought the truck needing intake manifold gaskets. While I was in there, it also got a MPFI upgrade and distributor as they were both trash. The motor was pretty sludgy under the valve covers and in the valley. Cleaned that up as best I could.
The good:
- Timing was set correctly with a scanner.
- Vacuum gauge shows on the low side of good, and steady throughout RPM ranges.
- Fuel pressure good and holding.
- I’m assuming the injectors are operating correctly, since they’re under the intake and I can’t test them individually. I did remove the upper intake again to make sure I installed the spider correctly and didn’t see anything out of place.
The bad:
- I have both P0300 and P0302 codes. DashCommand only shows misfire counts on 2.
- Compression on all cylinders is between 140-150 dry. Adding oil to #2 raised compression to 170, which seemed significant.
- All plugs show some oil fouling but I don’t run the truck much, and have tried new plugs with no improvement.
- Spark seems strong at the #2 plug (it shocked me) but pulling the plug wire while running shows no significant drop in idle, especially compared to other cylinders.
- Fuel trims are all over the place
Does that about cover it? Worn rings and/or heads? Can a mechanic do any additional scanning or diagnostics? Truck is in average condition for its age and I’m not sure it’s worth a crate motor, if it ultimately needs a new one.
Thanks for reading. Your thoughts are appreciated.
Tom
1997 GMC Sierra C1500
5.0 with 188k
Quick history:
Bought the truck needing intake manifold gaskets. While I was in there, it also got a MPFI upgrade and distributor as they were both trash. The motor was pretty sludgy under the valve covers and in the valley. Cleaned that up as best I could.
The good:
- Timing was set correctly with a scanner.
- Vacuum gauge shows on the low side of good, and steady throughout RPM ranges.
- Fuel pressure good and holding.
- I’m assuming the injectors are operating correctly, since they’re under the intake and I can’t test them individually. I did remove the upper intake again to make sure I installed the spider correctly and didn’t see anything out of place.
The bad:
- I have both P0300 and P0302 codes. DashCommand only shows misfire counts on 2.
- Compression on all cylinders is between 140-150 dry. Adding oil to #2 raised compression to 170, which seemed significant.
- All plugs show some oil fouling but I don’t run the truck much, and have tried new plugs with no improvement.
- Spark seems strong at the #2 plug (it shocked me) but pulling the plug wire while running shows no significant drop in idle, especially compared to other cylinders.
- Fuel trims are all over the place
Does that about cover it? Worn rings and/or heads? Can a mechanic do any additional scanning or diagnostics? Truck is in average condition for its age and I’m not sure it’s worth a crate motor, if it ultimately needs a new one.
Thanks for reading. Your thoughts are appreciated.
Tom
