Compression Test Readings

PILOTBILL

MEMBER
1983 GMC S15
6 CYL
2WD
AUTOMATIC
143,575 MILES

I have a 1983 GMC S15 Pickup with a 2.8L engine. Today, I ran both a Dry & Wet Compression Check on all 6 cylinders. I would like to know just what the reading mean. Reading for cylinder #1 was "DRY 120 PSI, WET 165 PSI". Reading for cylinder #2 was "Dry 135 PSI, WET 150 PSI". Reading for cylinder #3 was "DRY 130 PSI, WET 160". Reading for cylinder #4 was "DRY 135 PSI, WET 160 PSI". Reading for cylinder #5 was "DRY 135 PSI, WET 160 PSI". Reading for cylinder #6 was "DRY 135 PSI, WET 180 PSI". The truck has been running real bad this past few months. It all started the day after the engine backfired. I had to replace the Distributor, the Muffler and repair the Carburetor.

1 Reply

CARADIODOC

MECHANIC
33,752 POSTS

The readings are good. The higher wet readings means there is leakage past the piston rings but it probably isn't significant. A cylinder leakage test will confirm that as well as determine if there is excessive leakage past the valves or head gasket.