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Compression test - am I doing this right?

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    Compression test - am I doing this right?

    My 325i has had a misfire issue since I got it - rough idle and "puh-puh" sounds when revved.

    I've replaced all the ignition components, adjusted the valves w/ the little spring tool, and smoke checked for intake leaks, while replacing the intake manifold gaskets to be sure. The bitch tube orings were shot so I hoped that was my problem, but no dice.

    I decided to run a compression test since none of those things seemed to help. I'd noticed oil in the coolant when doing a flush - but the head looks pretty new to the car, so I couldn't tell if this was just leftover from a previous blown head gasket or something new.

    Anyways, I did the compression test when the engine was about 1/4 of the way up the temp gauge. I used a cheap Autozone rental. My readings were within 2-3 psi of 80psi across the board, with one 90psi and another 75.

    My question is, does this sound right? Can my engine even run with half the compression it's supposed to have? I tried to get the compression tool plug in there snug to make a seal, but I could only get it in there so tight.

    Just trying to determine what I should do about this misfire since nothing I've tried so far has fixed it. I'd hate to pull the head, replace the gasket, then have the same damn problem when I put it back on.

    #2
    That's really low. Are you getting a good seal? There's an Oring there too.

    Do it when the engine is at operating temperature.
    Originally posted by Gruelius
    and i do not know what bugg brakes are.

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      #3
      An o-ring between the spark plug and the head? There's a rubber o-ring on the compression tester bung...

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        #4
        That is a low reading, anything under a 90-100 is usually hard to start.

        Are you opening the throttle when testing? is it cranking over normal and not slow from a weak battery?

        I would check that tester on another car before taking that as a true reading.
        My M20 Frankenbuild(s)
        4 Sale - Fully Built TurnKey Megasquirt Plug and Play EMS

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          #5
          ^^^Bump for this..Make sure you stomping on the pedel when cranking, alsoo check the oring on the valve

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          [I][I]Turn the tapatalk signature off[/I][/I].

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            #6
            Tried two autozone testers, both with the same results. One of them actually blew a hole in the connector hose.

            I think I'm just going to pick up a quality leakdown tester, since I have an air compressor already.

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