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07-19-2013, 07:53 PM
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#1 |
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Registered User
Join Date: May 2013
Location: Prunedale California
Posts: 2
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Compression
Not sure what good compression should be I have 120 psi on all cylinders 1976 gmc Sierra grande 4x4 350
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07-19-2013, 09:37 PM
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#2 |
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Active Member
 
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: Compression
That should be okay. The rule of thumb is that there shouldn't be more than about 10-15% difference between highest and lowest. If the engine is not burning oil and otherwise runs okay, it should be okay.
When I test mine, I like to run the engine just long enough to coat the cylinders with oil, turn it off and remove all the spark plugs then do the compression test.
__________________
68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
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07-20-2013, 12:38 AM
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#3 |
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Registered User
Join Date: May 2013
Location: Prunedale California
Posts: 2
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Re: Compression
Ok thanks now that you mentioned it.the way I tested was I got home from work had new spark plugs,diddnt start it or anything like that,just as I would remove one plug I would test that cylinder then put new plug in.should I have warmed it up first or at least coat the wall like you said,I may get a different reading
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07-20-2013, 12:56 AM
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#4 |
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Registered User
Join Date: Jan 2010
Location: Louisa, Virginia
Posts: 30
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Re: Compression
Just as 68gmsee mentioned, all the spark plugs should be removed while performing the compression test. 120 psi on all the cylinders should be good as long as they are within 10-15% from highest to lowest. Any particular reason you're doing the compression test? Problems?
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