2nd Gen R56 Cooper S Most liked posts in thread: Need help performing a compression test

  1. ZippyNH

    ZippyNH Well-Known Member

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    #18 ZippyNH, May 26, 2014
    Engines are not like computers....
    As precise as they seem to be, they are highly variable, even when new...
    And as posted in your NAM thread....the length of the connector/hose makes a huge impact on the numbers.......useful in comparison to the same car at an earlier date, but no absolutes...important part is evenness of the numbers...high varration indicates an issue.
     
  2. oldbrokenwind

    oldbrokenwind Active Member

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    #4 oldbrokenwind, Apr 24, 2013
    Thanx for the info. I'll post my readings and any other helpful hints I come across --- hopefully today or tomorrow.
     
  3. DneprDave

    DneprDave Well-Known Member
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    #14 DneprDave, Jun 24, 2013
    Compression test gauges aren't expensive, get a new one with a short hard pipe that fits the MINI.

    Dave
     
  4. DneprDave

    DneprDave Well-Known Member
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    #17 DneprDave, May 26, 2014
  5. BThayer23

    BThayer23 Well-Known Member

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    #2 BThayer23, Apr 23, 2013
    Definitely pull all the plugs to get correct readings. I did the test on my R53 a couple months ago, and I had to crank each cylinder for 12 pulses so the gauge gave consistent readings. I think the starter does have a timer, but it shouldn't prevent the test.

    Not sure how direct injection affects things, but I pulled the fuel pump fuse and cranked it a few times to clear the fuel system before I pulled the plugs. I think the R56 has coil-over-plugs, too. Just make sure they're disconnected so you don't get any wayward sparks.
     
  6. BlwnAway

    BlwnAway Well-Known Member

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    #3 BlwnAway, Apr 23, 2013
    Don't know if the R56 is defferent but on 1st gen cars you pull the first (forward most) relay in the fuse/relay box under the hood, this is the relay for the ECU, basiclly shuts everything down.
     
  7. oldbrokenwind

    oldbrokenwind Active Member

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    #5 oldbrokenwind, Apr 24, 2013
    That didn't take long! Pulled plugs then the fuel pump fuse and cranked it for 10 - 15 seconds to clear fuel from the system. Found out that after the start button is pushed, it cranks for 17 secs before stopping by itself. Also discovered that while it's cranking, it can be stopped by pushing the button again. Seems obvious, but I was afraid to try it before prepping for this test. Still running the original battery - 62K miles and car was built in 9/07.

    Compression gauge with spark plug adaptor is about 2' long. I believe this long length causes readings to be low - at least I hope so.
    #1 = 105psi
    #2 = 105psi
    #3 = 115psi
    #4 = 115psi
    Dealer check 2 years ago was between 168 - 171psi. Not concerned about actuals, just variance. I'm happy with the results, but I'm also open for criticism ---
     
  8. BlwnAway

    BlwnAway Well-Known Member

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    #6 BlwnAway, Apr 24, 2013
    Yes, the adapter changes things and you are correct, as far as general health & running conditions go ypu're looking for variences as long as they are close to each other you shouldn't have many problems. (within reason of course)
     
  9. BThayer23

    BThayer23 Well-Known Member

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    #7 BThayer23, Apr 24, 2013
    huh. Looks like low variance, but also low readings. Was there anything that caused concern or is this just a status check?
     
  10. oldbrokenwind

    oldbrokenwind Active Member

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    #8 oldbrokenwind, Apr 24, 2013
    Month or so ago, I had the rear PCV hose connection blocked off --- BSH OCC installed on the driver side hose. This caused serious oil consumption --- crankcase pressure blocking the turbo oil drain line, so oil leaked thru the turbo seals into the turbo air inlet chamber, and mixed with the air. Totally defeating the purpose of OCC! Anyhow, I'm still seeing occasional smoky exhaust and wanted to ensure it wasn't rings / pistons, but residue in the air hoses / FMIC. So far, I'm convinced it's residue. The puddle inside the turbo inlet chamber is gone, after routing the rear PCV thru a "Tee" connection at the OCC.

    Lotsa opinions on the subject of OCC connections. I'm planning on a lengthy summary of my OCC installation by next month. Should be of interest to those with sudden high oil consumption. Will be a new thread.

    As for these low readings, I'm looking around locally for a shorter hose for my compression gauge. Maybe cut and splice my existing one. While shopping for a gauge, I saw some kits had short, metal adapters, instead of a hose. Didn't look like they would fit inside our spark plug well, so I opted for a hose.
     
  11. BlwnAway

    BlwnAway Well-Known Member

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    #9 BlwnAway, Apr 25, 2013
    Sort of wanted to clarify what I said, as far as "normal operation" goes, if there's too much of a difference between one or more of the cylinders the ECU will read it as a fault & give you a missfire code, if there's not the car should "act" normal, but if it were truly that low overall, even though the ecu isn't recognizing a fault there is a problem somewhere, I'd say a leakdown test is in order at least.
     
  12. ScottinBend

    ScottinBend Space Cowboy
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    #10 ScottinBend, Apr 25, 2013
    I would suggest (if possible) another compression test with a different gauge.....just to eliminate a possible calibration issue before paying for a leak down test. Seems odd that all the cylinders would be down equally.
     
  13. oldbrokenwind

    oldbrokenwind Active Member

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    #11 oldbrokenwind, Apr 30, 2013
    Shortened the compression gauge hose length with a splice from 23" to 16" and tested the low cylinder again, twice --- once hot then cold. Was expecting significant differences, but the cold (sat overnight) was 100psi and the hot was 95psi. Both down from the 105psi a couple days ago. I probably screwed up the splice, and have a small leak.

    Now that the leak down test has been explained, I'll bet thats what the dealer did for me a couple years ago. I can't believe my gauge is that far off, or that it's worn that much --- dealers 168 - 171 to my 105 - 115.

    Anyone have experience with the two different tests and their results --- on the same engine, in the same time frame?
     
  14. C.I.

    C.I. New Member

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    #12 C.I., Jun 18, 2013

    If it were your gauge, I would think you would get different readings on different tests, given if the gauge is faulty. I would think the odds of being faulty unlikely.

    run the test with the engine warmed to running temp.

    On my 04 R53, the test produced the following:
    #1-- 145
    #2-- 150
    #3-- 150
    #4-- 145

    hope that helps.
     
  15. DustinT

    DustinT New Member

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    #13 DustinT, Jun 24, 2013
    your readings are pretty low. Is this a gauge that you know is good? Could you borrow a known good gauge to compare results with? If you actually have that low compression, I think you'd see the car isn't running as well as it did when new.
     
  16. oldbrokenwind

    oldbrokenwind Active Member

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    #15 oldbrokenwind, Jul 29, 2013
    Bought a whole new gauge kit, just to get the correct hose size. First set of readings (post #5) was with the new hose and my old gauge --- it has better resolution between numbers. Tried it again last week with the new gauge (just one cylinder) --- no significant difference!

    Obvious conclusion, after squirting a little oil in the cylinder and getting an increase of about 20lbs --- shot rings. Still runs nice, but time to start considering the bottom end upgrades.
     
  17. genik

    genik Member

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    #16 genik, May 26, 2014
    What would be the default psi readings of a compression test for a 2008 R56S? Does BMW documentate the default readings somewhere in the manual?
     
  18. oldbrokenwind

    oldbrokenwind Active Member

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    #19 oldbrokenwind, May 26, 2014
    Like Dave says --- nothing in the manual! However, when a dealer checked my '07S, at my request, they documented the following --- "All cylinders are within 5% of each other and between 160-180 PSI. Checked OK." Don't know where they got these numbers, maybe a manual not available to the general public? I put a lot of faith in this dealership's service dept. Can't say the same for all of them.