Strange compression test results

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kathol233
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Strange compression test results

Post by 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?
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sparky72
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Re: Strange compression test results

Post by 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.
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1972 F250 Ranger XLT 2wd / 8100 GVW / 390 / T18 / 3.73 D60
davelj
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Re: Strange compression test results

Post by 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
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Re: Strange compression test results

Post by 69 F250 »

maybe the compression tester broke?
1969 ford f250 camper special c6 automatic 360ci under powered
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My427stang
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Re: Strange compression test results

Post by 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
71 F-100 SB 4x4, 461 FE, Edelbrock Pro-flo 4, 4 speed, 4 inch softride lift, all poly bushings, integral PS, most mods installed since the 80's
70 Mustang Sportsroof 489 FE, EFI, TKO-600 5 speed, 4.11s
Engine building by-appointment only--30+ years, specializing in strong street pump gas FEs
Mercury100
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Re: Strange compression test results

Post by Mercury100 »

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