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On Friday we did a compression test on my 87 with 122k. I'm aware that I had bad test results but I'm looking for advice on what would be the cause. I will attach photo of the results, but here's some background info:
-Passenger side cat was blocked up and red hot and kept decent flow out of the muffler, driver side pipes (already true duals) had significant leaks and had less flow from the muffler than the blocked cat
-2 bad plug wires were found on tear down -there was oil leaking from all around the intake base
-Surprisingly the Master Mechanic taking lead on this said the plugs and exhaust burn looked pretty good
-After a few "while we're at it" moments my l98 is currently sitting on a work bench with 2 sets of compression tests done, I'm currently trying to get my hands on a proper stand.
Plans leading to the "while we're at it" include:
long tube headers
cat delete
full stainless dual exhaust
Ambitions depending on how expensive it is to fix my compression related issues:
-First TPI, or some porting with ASM runners
New heads, or Port and Polish existing heads with new springs
First compression test is to max psi
Second is to 4 strokes, wide open throttle as per the book. First compression test is to max psi Second is to 4 strokes, wide open throttle as per the book.
Last edited by pwbs87; Aug 20, 2023 at 02:11 PM.
Reason: additional info
I should also mention that while one cat was red hot and the other pipe had a 1.5 inch hole there was still flow out of both mufflers, a lot more out of the one with a blocked cat
At this point do a leakdown. Will tell you exactly whats going on. If it overheated bad, you most likely have some tuliped valves, but the test will show that.
I agree with doing the leakdown test. The key thing on the leakdown test is to figure out where the air is leaking - if it's into the intake or exhaust - you have a valve issue - if it's leaking into the crankcase - that's indicative of a bad rings.
The compression test numbers are not good, but not horrible, You may find that you can get away with a valve job (or new heads) - a lot will depend on how well the owner(s) maintained the vehicle. It's really not that common to see the short block in bad shape when nothing mechanical happened to the car (e.g a dropped valve) - and when the owners did regular oil changes.
L98 compression test results
