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random compression readings on one cylinder

Posted by eli96talon, Mar 1, 2012

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  1. eli96talon

    eli96talon Proven Member

    113
    0
    Joined Feb 16, 2012
    mt.pleasant, Texas
    I was wondering if anyone can explain why I keep geting strange compression readings on cylinder 3.sometimes its at 90 then at 120 then at 145 then 130.the compression goes up and down any way it wants. Also its not the tester,when i comp. Test the other cylinders they always read 185,184,185 it never changes.can anyone tell me why this is happening?
     
  2. Twinturbo120

    Twinturbo120 Supporting VIP

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    Joined Aug 14, 2010
    Miami, Florida
    Have you tried doing a "wet" compression test to see what happens?
     

    Street Build 506  1

    1995 Eagle Talon TSi AWD
    awd · manual · 2G DSM
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  3. bryanwheat

    bryanwheat DSM Wiseman

    6,978
    171
    Joined Aug 16, 2004
    Columbia, Missouri
    You probably have a bunch or carbon on the valves and combustion chambers. When the reading is low there is likely a piece of carbon between the seat and valve, when it burns out the compression goes higher. Either that or you have a junk compression tester.
     
  4. spic21

    spic21 Proven Member

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    Joined May 14, 2010
    albany, Louisiana
    if this is the case try so sea foam, ive seen it work miracles with build ups.
     
  5. BogusSVO

    BogusSVO Proven Member

    5,714
    287
    Joined Jul 1, 2009
    Pensacola, Florida
    Run a leak down test.

    You may have an excessivly worn guide in the head that allows the valve to seat at a cocked angle
     
  6. eli96talon

    eli96talon Proven Member

    113
    0
    Joined Feb 16, 2012
    mt.pleasant, Texas
    The head is 2 weeks old all the componants are new,the headgasket is also new..there is no carbon build up on the valves.I also did a wet test to see if the compression would go up and it didn't.its just strange on day the compression is low and misfiring then 2 hours later its high,then low,then high.
     
  7. iugrad92turbo

    iugrad92turbo Supporting Member

    10,549
    439
    Joined May 22, 2007
    Kalamazoo, Michigan
    Sounds like something is still wrong, maybe there was a problem with the guides in the head, i learned never to assume things. Head may be fairly new but, you could have a problem in there, regardless.
     

    7K  5

    1992 Eagle Talon TSi
    awd · manual · 1G DSM
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  8. eli96talon

    eli96talon Proven Member

    113
    0
    Joined Feb 16, 2012
    mt.pleasant, Texas
    Im puting in am order to s.I.m for a fresh block since I don't have any trust in this motor.also I have issues that when under boost the #3 piston pushes the spark plug gap closed shut
     

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