Compression numbers for the North*
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Northstar Engines and System Technical Discussion Discussion, Compression numbers for the North* in Cadillac Engine Technical Discussion; I own a 98 concours with 168000 on th odo and am about to do a compression check on all ...
  1. #1
    fristim is offline Cadillac Owners Fanatic
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    Compression numbers for the North*

    I own a 98 concours with 168000 on th odo and am about to do a compression check on all the cyls. Just wondering what are the numbers suppose to be for the PSI on a healthy motor. Im also doing a wet compression check and was wondering if that would be ok to do on this motor, I really dont wanna mess up my o2 sensors or any thing. Any feed back would be greatly appreciated as I surely dont wanna screw any thing up. Thanks a lot and remember: DRIVE IT LIKE YOU STOLE IT!

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Compression numbers for the North*

    I think the important thing on a compression check is that all cylinders are within 10% (if memory serves me correctly) of each other. Actual psi is not important but I would guess they'd be in the 150-175 range?

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: Compression numbers for the North*

    I tested mine about a month ago, but forgot the numbers... sorry

  5. #4
    parts68 is offline Cadillac Owners Fanatic
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    Re: Compression numbers for the North*

    just did a 95 rora with 160K. dealer said it had 2 dead cylinders.
    lowest was 185,highest was 225.
    I decarbonized it and the highest went down to 205 which was much better.
    still trying to figure out what cylinder was dead(not).Runs smooth as silk after new plugs.

  6. #5
    Zorb750 is offline Cadillac Owners Connoisseur
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    Re: Compression numbers for the North*

    Should be around 180.

  7. #6
    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: Compression numbers for the North*

    Make sure you do the compression testing with the throttle propped open wide and a good hot battery. Both common reasons for wierd results.

  8. #7
    parts68 is offline Cadillac Owners Fanatic
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    Re: Compression numbers for the North*

    and a warmed up engine ,all plugs removed.
    Zorb I think 180 is low,see my results with a 95 and 160K on clock.
    FSM says 140-170 but thats terribly low so it cant be right.

  9. #8
    Raze's Avatar
    Raze is offline Cadillac Owners Enthusiast
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    Re: Compression numbers for the North*

    A leak down test is more conclusive, search around the procedure has been documented a number of times.

    The Factory Service Manual for my 98 ETC has the list at 140-170psi at cranking speed with throttle open

  10. #9
    Eldobroken's Avatar
    Eldobroken is offline Cadillac Owners Fanatic
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    Re: Compression numbers for the North*

    Quote Originally Posted by Ranger
    I think the important thing on a compression check is that all cylinders are within 10% (if memory serves me correctly) of each other. Actual psi is not important but I would guess they'd be in the 150-175 range?
    Exactly what I would have said. As long as there all close your ok.

  11. #10
    Zorb750 is offline Cadillac Owners Connoisseur
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    Re: Compression numbers for the North*

    No. As long as they are all close and all high enough you are ok.

  12. #11
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    auroradude is offline Cadillac Owners Fanatic
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    Re: Compression numbers for the North*

    I'll be doing 1 on mine before i get a new car. I did the Auto-RX treatment twice before, and let me tell you it dfeintaly runs better after that. Im sure that cleaned up the compression somewhat, and the filler hole looks worse on the before pictures.

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