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i've been on here for the past few months posting about engine trouble with my wife's 2020 tahoe l86 that has 90k miles, and i believe i've narrowed it down to piston rings or similar on cylinder 8. i'm seeking advice on what process i should take when attempting to repair it.
i had the engine down to the block a couple weeks ago, but i made the (painful) mistake of not doing compression and leakdown tests _before_ taking it apart. after rebuilding the top half of the engine and doing a dod delete, i started getting misfires on cylinder 8 again after startup. i did compression and leakdown tests on all 8 cylinders. for compression i got 225-240 psi everywhere except cylinder 8, which had 95. i added a couple squirts of engine oil to the cylinder and redid the compression test, which gave 125. for leakdown, i got 12-18% loss for all cylinders except 8, which gave 85%+. when i covered the pcv tubes on the valve covers during leakdown on cylinder 8, it would spray oil from the dipstick tube. additionally, when idling with the oil cap off, air surges out of the oil cap pretty forcefully. both the service manual and what i've read elsewhere suggest this indicates a piston ring failure or similar.
now that i've diagnosed the issue properly, i'm wondering what the best approach is to do the repair. i'm already familiar with the process of removing the heads and oil pan, but it isn't clear to me whether doing this as an engine-in procedure is better than doing it engine-out.
when i disassembled the engine previously, i did not see any visible scoring or damage to the cylinder bore or any cracks. if the bore is substantially scored or the block damaged, i assume i would have to remove the engine anyways. thoughts on whether i should pull the engine or not for this repair? i've not pulled an engine before, so i'd need to read up and get equipment.
assuming there is no other substantive damage, does it make sense to replace just the piston rings on the damaged cylinder or should i replace the rings on all the cylinders?
in the meantime, i will be reading up on how to remove the engine to assess that route versus attempting the repair engine-in.
i had the engine down to the block a couple weeks ago, but i made the (painful) mistake of not doing compression and leakdown tests _before_ taking it apart. after rebuilding the top half of the engine and doing a dod delete, i started getting misfires on cylinder 8 again after startup. i did compression and leakdown tests on all 8 cylinders. for compression i got 225-240 psi everywhere except cylinder 8, which had 95. i added a couple squirts of engine oil to the cylinder and redid the compression test, which gave 125. for leakdown, i got 12-18% loss for all cylinders except 8, which gave 85%+. when i covered the pcv tubes on the valve covers during leakdown on cylinder 8, it would spray oil from the dipstick tube. additionally, when idling with the oil cap off, air surges out of the oil cap pretty forcefully. both the service manual and what i've read elsewhere suggest this indicates a piston ring failure or similar.
now that i've diagnosed the issue properly, i'm wondering what the best approach is to do the repair. i'm already familiar with the process of removing the heads and oil pan, but it isn't clear to me whether doing this as an engine-in procedure is better than doing it engine-out.
when i disassembled the engine previously, i did not see any visible scoring or damage to the cylinder bore or any cracks. if the bore is substantially scored or the block damaged, i assume i would have to remove the engine anyways. thoughts on whether i should pull the engine or not for this repair? i've not pulled an engine before, so i'd need to read up and get equipment.
assuming there is no other substantive damage, does it make sense to replace just the piston rings on the damaged cylinder or should i replace the rings on all the cylinders?
in the meantime, i will be reading up on how to remove the engine to assess that route versus attempting the repair engine-in.
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GM has been having a lot of issues with those engines. One problem is that they are a lot higher compression than the 5.3 and 6.0 and really require 93 octane fuel. My friend was running mostly 87 in his and was not aware that it needed the higher octane. The Direct Injection engines also have a problem with what is called Low Speed Pre-ingnition. Here is a good article on it.
