Strange compression test results

[kathol233]

I've got a 1971 F100 with a stock 302, holley 650 and headers. Truck will not idle, spits and sputter and dies while driving it. Took a compression test on it with these results. #1 - 120 lbs. #2 - 116 lbs. #3 - 115 lbs. #4 - 135 lbs. #5 - 0 lbs #6 - 50 lbs. #7 - 85 lbs #8 - 75 lbs. I know the o lbs is not good but why would one side be up there and the other side be down?

[sparky72]

Loose or broken head bolts, perhaps. Or a cracked block. It would be odd for a gasket to fail that completely, but it is possible. I would be taking the head off to inspect regardless.

[davelj]

Was any work done recently? Was it running OK and then just started having problems? Are the heads a matched pair?

I'm thinking a valve adjustment issue but more info would help. Pull the valve covers and look for any miss matched parts from side to side.

[69 F250]

maybe the compression tester broke?

[My427stang]

I would guess head gasket issues, potentially stuck valves, or bad cam. All on one side more likely head gasket failing

Good point on checking again though, be sure your numbers are repeatable

[Mercury100]

Always do a compression test with the carb wired wide open.