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M20 went boom

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    #1

    M20 went boom

    so last night i left my apartment to run an errand and out of nowhere...BOOM. Sounded like a tire exploded or something of the like. So i immediately looked at my gauges and saw the RPMs were getting below 500 so I shut off the engine and coasted to the 4 way stop i was approaching. and i probably shouldnt have done this but i decided to start it back up to try and get around the corner and then i shut it off as soon as i turned and coasted to a parking lot. but when i turned it back on..it started fine and ran, but it was rough. so i parked and immediately wondered about the new timing belt i put on a month ago. i pulled that little black plastic back cover off and broke it to pull it out. the belt had tension with just a little play and didn't appear to have snapped from what i could see with that limited space. i know for a fact when i did my belt everything was perfectly in time, the belt had good tension, new tensionor pulley and spring etc. I went the whole 9 yards with this tbelt replacement because i was originally considering replacing my head gasket for the heck of it. and then a couple weeks after doing the timing belt and thermostat (water pump is fairly new), i replaced the oil filter housing seals and stopped my oil leak. ever since the oil leak was fixed it started making a weird noise like a muffled sewing machine. and before i replaced the thermostat, the old one was causing it to overcool to the extent that in the winter, it wouldnt get out of the blue. ive also recently replaced my cat and all sort of ignition and seals. The one thing i havent done lately is adjust my valves. If you guys have any clue what this may be let me know. i'm gonna start tearing the engine apart this weekend and double check the timing belt and valves before i try to rotate the engine by hand.

    Sorry for the long post...figured some background might help
    Tags: None
    #2
    Timing belts are quiet failures. I'm guessing a backfire in the intake somewhere that caused a vacuum leak.
    Lorin


    Originally posted by slammin.e28
    The M30 is God's engine.

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      #3
      ^ that sounds pretty reasonable to me.
      AWD > RWD

      Comment

        #4
        I just replaced the intake manifold gaskets and all sorts of other things intake/ignition related. No fluids leaking either btw, meant to say that in my big post. Ill be tearing it apart this weekend but the back fire sounds a lot better than a messed up piston or valve.

        What could have caused the backfire? As i said it was making that weird noise after i fixed the oil leak.

        Comment

          #5
          Did you blow the intake boot off/blow a hole in it?

          My e28 did that in the HS parking lot. It was a very loud bang! Then car ran like dogshit and shut off. Wouldn't restart. Looked under the hood, I didn't tighten the intake boot enough and it blew off.
          1974.5 Jensen Healey : 2003 330i/5

          Comment

            #6
            Was still on from what i can remember. Ill look over the intake after work and post what i find. Crossing my fingers on this!

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              #7
              My e24 backfired once and it blew the plug out of the connector for the AFM, car ran like shit until I found the problem. Reconnected it and it was fine after that. As a note, the connecter clip was partially broken before this but it has always stayed in place. It has back fired a few times when I've been doing work on the car since then, every time it blows the plug out of the connector.
              90 325i DD/Track
              03 Durango 5.9


              Originally posted by e30mpg
              It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

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                #8
                What could have caused the back fire though?

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                  #9
                  The intake manifold, throttle body, intake boot, afm, fuel rail, fuel pressure regulator, and all vacuum hoses looked good...

                  Im just hoping i didnt get a faulty timing belt and a tooth is missing or something causing the timing to be off...causing the backfire. Ill look at the belt tomorrow

                  Comment

                    #10
                    Broken Rocker arm?
                    I blew one right past the adjuster on the intake side, so I still had contact to the valve, so it idled "ok" but it ran under load like I lost a cylinder. Easy thing to check.
                    https://www.forabodiesonly.com/mopar...re-irs.356333/

                    This Forum is built on love, and powered by Sexual Tension!

                    When I die, I want to go peacefully like my Grandfather did, in his sleep -- not screaming, like the passengers in his car.

                    Comment

                      #11
                      Originally posted by MonkeyMadness View Post
                      Broken Rocker arm?
                      I blew one right past the adjuster on the intake side, so I still had contact to the valve, so it idled "ok" but it ran under load like I lost a cylinder. Easy thing to check.
                      Good point, ive got tomorrow off so here in a bit, when i get home, ill take the valve cover off and inspect it. Hopefully not though. What all could happen if the rocker arm breaks?

                      Comment

                        #12
                        ^ Street car valvetrain failure of any kind is a relatively mild sounding event. No explosion sounds. If you are worried about valve to piston lovin' start with a leakdown test. I still say vacuum leak.
                        Lorin


                        Originally posted by slammin.e28
                        The M30 is God's engine.

                        Comment

                          #13
                          Originally posted by LJ851 View Post
                          ^ Street car valvetrain failure of any kind is a relatively mild sounding event. No explosion sounds. If you are worried about valve to piston lovin' start with a leakdown test. I still say vacuum leak.
                          Even though all vacuum hoses are in good condition and all gaskets are new? I looked over everything including the intake manifold itself to make sure there were no cracks.

                          Comment

                            #14
                            Originally posted by jw 325ic View Post
                            Even though all vacuum hoses are in good condition and all gaskets are new? I looked over everything including the intake manifold itself to make sure there were no cracks.
                            My crystal ball is on the fritz right now, it's up to you.
                            Lorin


                            Originally posted by slammin.e28
                            The M30 is God's engine.

                            Comment

                              #15
                              Originally posted by LJ851 View Post
                              My crystal ball is on the fritz right now, it's up to you.
                              Ha! Im gonna take the valve cover off tonight and then the timing belt cover off tomorrow and check it all out.

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