Z28chris
TYF Newbie
- Joined
- May 14, 2022
- Posts
- 6
- Reaction score
- 11
Hey guys, I have a 2001 Tahoe LT with the 5.3 L Vortec LM7 engine ("T" VIN code) and about 150000 miles. Two weeks ago the engine started misfiring with the P0308 code. I also heard a loud ticking from the engine bay, so obviously I supected, that something with the lifters has gone bad. Also the ticking came from cylinder 8.
After taking off the valve cover and fiddling with the rockers, I saw, that the second rocker from the back was moving about a 1/4 inch up and down. So I'm guessing the lifter for this valve has collapsed.
Before taking off the cylinder head I wanted to check the compression and here are the results:
This is the first time, I checked the compression on an engine, so I wanted to ask you guys for help. Do you think I should replace the cylinder heads, according to these numbers?
Since I already have to take them off, I wouldn't want to reuse them, if they were bad. Of course I still have to check them, when I have taken them off, but I thought the compression test would be a great help here.
From what my Haynes repair manual tells me (minimum compression pressure 100 psi; maximum variation between cylinders 25 % from the highes reading), I would be guessing, that these values should be OK-ish. The lowest value is 115 psi for cylinder 4 (so 15 psi above the minimal pressure) and the variation from this to the highest reading would be about 16 % (22 psi difference from the 137 psi reading of cylinder 3).
What do you guys think? Would you recommend getting new cylinder heads, by looking at these numbers? Or would you rather save the money and reuse the old ones?
After taking off the valve cover and fiddling with the rockers, I saw, that the second rocker from the back was moving about a 1/4 inch up and down. So I'm guessing the lifter for this valve has collapsed.
Before taking off the cylinder head I wanted to check the compression and here are the results:
Cylinder | dry | wet | difference dry to wet |
1 | 130 psi | 135 psi | 5 psi |
3 | 137 | 145 | 8 |
5 | 132 | 137 | 5 |
7 | 131 | 140 | 9 |
2 | 130 | 150 | 20 |
4 | 115 | 135 | 20 |
6 | 127 | 150 | 23 |
8 | 125 | 137 | 12 |
This is the first time, I checked the compression on an engine, so I wanted to ask you guys for help. Do you think I should replace the cylinder heads, according to these numbers?
Since I already have to take them off, I wouldn't want to reuse them, if they were bad. Of course I still have to check them, when I have taken them off, but I thought the compression test would be a great help here.
From what my Haynes repair manual tells me (minimum compression pressure 100 psi; maximum variation between cylinders 25 % from the highes reading), I would be guessing, that these values should be OK-ish. The lowest value is 115 psi for cylinder 4 (so 15 psi above the minimal pressure) and the variation from this to the highest reading would be about 16 % (22 psi difference from the 137 psi reading of cylinder 3).
What do you guys think? Would you recommend getting new cylinder heads, by looking at these numbers? Or would you rather save the money and reuse the old ones?