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Thread: Insight? First compression test

  1. #1
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    Insight? First compression test

    Hey I just ran a compression test on my s50. My lowest cylinder was number 6 at around 135. 1-5 were all 140-145. I got these numbers on two tests. I'm happy to see the numbers are fairly consistent but over all is this low-ish compression on an s50 with 115k?

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  2. #2
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    Very very low, especially at your elevation (276ft based on your location).

    Get a new tester of quality and try the test again. Make sure you are connected to a strong battery charger, the motor is warm, that you are holding the throttle WIDE OPEN during the test, and that you are cranking till the numbers peak (usually 12-16 cranks).
    Last edited by Braymond141; 09-16-2018 at 03:20 PM.

  3. #3
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    Hmm. I bought the highest rated tester on Amazon. Car was at operating temperature and I had throttle wide open. My buddy said I was peaking at about 4 cranks. Each cylinder I gave it about 8 cranks

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  4. #4
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    I’ve never seen any of these motors peak at 4 cranks unless using oil for ring diagnostics. I still suspect the tester.

  5. #5
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    MauiM3Mania is offline Observer/Master Skeptic Moderator
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    OP, did you pull the fuel relay? If not, fuel will wash the walls and throw off the readings significantly.
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  6. #6
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    stock cams, timed correctly (ie, not too much overlap?) Numbers are low, but consistent, so that's definitely good.
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  7. #7
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    Insight? First compression test

    As far as internals go this is a completely stock motor. I have no idea on timing as I've never checked it. Yes I ran it for a good drive and pulled it in. Then I pulled the fuel pump fuse and started pulling the plugs
    Last edited by AlpineM3OldAsMe; 09-16-2018 at 04:41 PM.

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