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compression check

This is a discussion on compression check within the General Help forums, part of the LSx Technical Help Section category; when i bought the z28 the guy said it had a cracked #2 piston and it was throwing codes, i ...

  1. #1
    El Toro Grande jaslivers's Avatar
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    1958 chevy pickup 283
    02 gmc z71 5.3L white

    compression check

    when i bought the z28 the guy said it had a cracked #2 piston and it was throwing codes, i took it in and there were no codes/no check engine light

    well today i got a compression check done and it was a little under 20%
    is that good, bad, ugly? any help would be nice

    the car runs amazing with no miss/sputtering

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    Did you check all 8 cylinders, or just No. 2? Generally, you should check all 8 and then look for the variance between cylinders. My recollection is that they should all be within 10%-15% of one another, meaning if that your high is 140 p.s.i., your lowest shouldn't be any less than 120 p.s.i. (This is by way of example only and is not indicative of actual stock compression). You should then perform a leak down test to continue the diagnosis from there. Someone here can probably tell you what stock compression should be...

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    El Toro Grande jaslivers's Avatar
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    1958 chevy pickup 283
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    hmm we only did the one

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    You can also check the top of the piston for damage with a bore scope. Does it seem to make any noise or are you getting excessive blowby from the PCV?

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    El Toro Grande jaslivers's Avatar
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    1958 chevy pickup 283
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    negative, everything runs/sounds fine

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    Senior Member bills98ta's Avatar
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    Sounds like someone got a bargain !!!

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    El Toro Grande jaslivers's Avatar
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    1958 chevy pickup 283
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    haha thats what im hoping i got the car for about half of what others are going for
    2001 artic white z28, m6, lid, exhaust, 62k miles

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    Moderator Cutlass's Avatar
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    If you just did one and you got 20 %, it sounds like you did a leak down test. 20% leak down is ok, not great but ok.
    Do the other cylinders for comparison and do a compression test also. post the results

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    El Toro Grande jaslivers's Avatar
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    will do, it might be a few days, car is at the body shop

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    Member 99yellowz28's Avatar
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    1999 camaro m6

    dose anyone know what stock compresion is because mine was between 140-150

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    Impounded 86 IROC-Z's Avatar
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    Is "TPI" stamped onto the top of the engine?

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    Member Blue_01_Z28's Avatar
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    Quote Originally Posted by 99z-28 View Post
    dose anyone know what stock compresion is because mine was between 140-150
    My engine has stock compression and I checked it last night. The cylinder I checked was right at 150.

  13. #13
    Member 99yellowz28's Avatar
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    Quote Originally Posted by Blue_01_Z28 View Post
    My engine has stock compression and I checked it last night. The cylinder I checked was right at 150.
    im gussing that is what its supposed to be sounds about right

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