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    #1

    Compression test

    I changed the rear rotors/pads and changed the oil and filter tonight after work before I went home. The boss was around and was like, "your car is missing on a cylinder." I knew it had been running rough at idle for a long time but I didnt think about it cus I dont really care lol. I thought, "meh, its an old car. I dont care. I'm not gonna worry about it." Well... A little over a month ago probably I drove to Ohio and back which is about a 5hr round trip. It was a night drive and I noticed on the way there the car was missing every once in a while at highway speeds. On the way back it just kept getting worse to where the car would buck REALLY bad. It was late so I was gonna check on it the next morning. When I went to check on it, it didnt miss like it did before so I just dismissed it and said fuck it until it comes up next. It hasnt happened since then and right now its just idling rough. When you rev it up it doesnt seem to be a big problem. We pulled spark plugs and they looked ok. Ended up doing a compression test. That was some bad news and I didnt know that it was as bad as it was. The numbers were as follows:

    Cyl 1 - 120
    Cyl 2 - 94 or so
    Cyl 3 - 73 !!!!! WTF?!?!?!?!?!??!
    Cyl 4 - 94 or so
    Cyl 5 - 120
    Cyl 6 - 130

    So... the engine only has 171k miles on it. The compression on a good engine should be around 140-150 and consistent in all cylinders right??? Pretty much something in Cyl 2-4 is fucked up. I could deal with all of em being 120-130. But 70-90??!?!?!?!!! WTF?! So... next week we are gonna do a cylinder leakage test and try and figure out what the problem is. I've officially decided... my car is a beater. It really sucks though because the week before Christmas I hit a van and I'm not fixin it ;) Now the engine thing. If its a big problem, I am just gonna find a decent used m20b25 and swap engines. Just lettin everybody know :) Sorry about the long post.

    Will
    RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
    Welcome e30 (brilliantrot '90 325is) 12/23/06
    DaveCN = Old Man
    My signature picture was taken by ME! Not by anyone else!



    Originally posted by george graves
    If people keep quoting me in their sig, I'm going to burn this motherfucker down.
    Tags: None
    #2
    clearly the answer is to stick a turbo on it

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      #3
      yeah those #s are all over the place and very low in general. Mine were ~150 across the board with a stock motor, and about ~165 after my headwork, with 175k on the bottom end.
      Build thread

      Bimmerlabs

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        #4
        lol Thats what I thought. oooooo low compression. Turbo time beyotch! I'll just go to Lowe's and pick up some white PVC tube for my piping and pick up a turbo from the junkyard.

        Will
        RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
        Welcome e30 (brilliantrot '90 325is) 12/23/06
        DaveCN = Old Man
        My signature picture was taken by ME! Not by anyone else!



        Originally posted by george graves
        If people keep quoting me in their sig, I'm going to burn this motherfucker down.

        Comment

          #5
          Originally posted by nando
          yeah those #s are all over the place and very low in general. Mine were ~150 across the board with a stock motor, and about ~165 after my headwork, with 175k on the bottom end.
          Yea. I cranked the car while my boss checked the compression. He got this really bad face on cyl2, 3, and 4. I asked him the numbers as he did each cylinder and when he said cyl2 I freaked out a little bit. Then he went to cyl3. He said 73 and I was like... holy shit....... lol So... I dunno if I wanna just find a used decent engine from another car, or just finding the problem and fixing this one. If anybody has an m20b25 they wanna get me for cheap... let me know ;)

          Will
          RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
          Welcome e30 (brilliantrot '90 325is) 12/23/06
          DaveCN = Old Man
          My signature picture was taken by ME! Not by anyone else!



          Originally posted by george graves
          If people keep quoting me in their sig, I'm going to burn this motherfucker down.

          Comment

            #6
            Judging from what you've posted, I would say that you've got a blown headgasket. Check the coolant for oil, and oil for coolant. Its probably worth doing another compression test just to rule out any errors with the first one.
            '91 318is
            sigpic

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              #7
              I guessed the same thing as Brew.

              but like Will said on AIM, it could be a lot of things.

              Comment

                #8
                are you sure you cranked it over the same number of times? usually 3 or 4 times.

                But if so, i would check for blown headgasket or something. Maybe even a warped head.

                Kyle
                1988 M3, 97 840, 99 XJ
                DILLIGAF

                Comment

                  #9
                  Originally posted by rwh11385
                  I guessed the same thing as Brew.

                  but like Will said on AIM, it could be a lot of things.
                  Well, there aren't too many other things that will cause three adjacent cylinders to have low compression. Usually when a headgasket lets go, it leaks compression between cylinders, and causes exactly the sort of numbers that Will's motor got.
                  '91 318is
                  sigpic

                  Comment

                    #10
                    Hmm... well I figure it could be a headgasket, valve seats, or piston rings. But yea, I thought originally the head gasket because of those 3 cylinders. The one in the middle being 73 and the 2 surrounding it being the same as well (around 94). Then the other 3 cylinders being fine. I just drained the oil tonight and switched to Amsoil synthetic. Think I should just buy another head and rebuilt it and put it on there? That might actually be the most cost effective... Timing belt/Water pump needs to be changed in 20-30k miles anyways lol

                    Will
                    RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
                    Welcome e30 (brilliantrot '90 325is) 12/23/06
                    DaveCN = Old Man
                    My signature picture was taken by ME! Not by anyone else!



                    Originally posted by george graves
                    If people keep quoting me in their sig, I'm going to burn this motherfucker down.

                    Comment

                      #11
                      Originally posted by PeaveyBassist
                      Hmm... well I figure it could be a headgasket, valve seats, or piston rings. But yea, I thought originally the head gasket because of those 3 cylinders. The one in the middle being 73 and the 2 surrounding it being the same as well (around 94). Then the other 3 cylinders being fine. I just drained the oil tonight and switched to Amsoil synthetic. Think I should just buy another head and rebuilt it and put it on there? That might actually be the most cost effective... Timing belt/Water pump needs to be changed in 20-30k miles anyways lol

                      Will
                      I'd get yourself a full top-end gasket set, timing belt/water pump/cap/rotor/etc, and then pull the head. Get it checked by a machine shop for any warpage or valve leakage. Probably a good time to throw a hotter cam in there.
                      '91 318is
                      sigpic

                      Comment

                        #12
                        We got a couple heads at work I think I could rebuild. This is my only car because I'm only 18 and work part time while going to school. I figure I can rebuild a different head and just swap heads and stuff on a Saturday at work. I would have the shop owner who has been working with BMW and Mercedes for 15 years help me so I would do it right. If I did it, I would fuck it up for sure. Change timing belt and water pump while I am in there too of course even though I changed them 25-30k miles ago.

                        Will
                        RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
                        Welcome e30 (brilliantrot '90 325is) 12/23/06
                        DaveCN = Old Man
                        My signature picture was taken by ME! Not by anyone else!



                        Originally posted by george graves
                        If people keep quoting me in their sig, I'm going to burn this motherfucker down.

                        Comment

                          #13
                          you have no choice but to replace the timing belt, doing anything otherwise would be M20 suicide. :(
                          Build thread

                          Bimmerlabs

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                            #14
                            Will, sorry about your luck on that. I might know where you can get a good M20 on the cheap. You remember that guy who sold you the diff . . . ?

                            Its really a bad stretch of luck you have had lately. Before your little fender bender and this, I felt that you had a very nice car. Of the ones up at alex's place, yours was one of the cleanest, nicest ones there.
                            Last edited by Dave; 01-07-2006, 07:23 AM.
                            Current Cars
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                              #15
                              The easiest way to see what is causing the low numbers is to do another compression test as you have already done. Squirt ~tsp of normal dyno oil, thicker the better, into the cylinder through the spark plug hole. Give it some time to work its way around the rings. This will temporarily restore compression lost through bad rings.

                              If your numbers come out good this time its your rings.. if not its likely bad valve seating or a blowing head gasket.
                              Tenured Automotive Service Professional - Avid BMW Enthusiast

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