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Full M42 rebuild - timing off

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    Full M42 rebuild - timing off

    E21 m42 swap, '95 long block, 91' ECU and intake. I can get more specific if need be but I think the platforms are nearly identical.

    I finally got the engine in and wiring set. I tried to do a test crank and after 10-20 seconds of cranking, nothing.

    This morning, tried to crank it again except I left the fuel prime. When I hit ignition, almost immediately, I hit a huge misfire and the ICV hose blew off.

    A few basics, I see spark when the plugs are pulled, I know fuel is there (high pressure line wasnt fully tight and had a bit of a leak)

    More importantly, I fear that timing is WAY off. Maybe I set TDC at exhaust and not compression. My oil reeks of gas so it must be seeping past the rings when Im not getting ignition.


    1) How can I confirm TDC is at compression and not exhaust stroke?
    2) Any other variables that can have timing off?


    I get that the arrows on the cam sproket should be up, the lobes at the front should point to each other at 45degrees, and the squares at the back of the cam should be level. I just cant figure out how to confirm which cycle im on

    Thanks for any help. If I have the wrong idea, let me know...

    #2
    I'm 95% timing is ok just wanted to make sure.

    I was wondering, there are pegs that are on the cam gears both are in sync around 7 o clock on the gear. Ive seen some images where cam is tdc and the pegs are opposing, at 7 on the intake and 4 o clock on the exhaust. What's the correct way here?

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      #3
      See here for some info on correct timing:
      https://www.r3vlimited.com/board/sho...d.php?t=374858

      If the timing is good, maybe verify that the coil packs are wired properly and connected to the correct plugs?

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        #4
        If you want to know if your on the correct stroke hook a leak down test on it. If your showing like 80 percent leak down. Rotate the engine again to TDC and retry your leak should be minimal which means thats the stroke you want to be on.


        1989 325is l 1984 euro 320i l 1970 2002 Racecar
        1991 318i 4dr slick top


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          #5
          Good idea on the leakdown test. I need to try that.

          I will verify the coil packs are correct. That's a good idea since I wasnt 100% sure but should reverify. I didnt think I could mess it up based on how the wiring is set up but its totally plausible.

          I ran a compression test and I dont think it was *damning* but it's not great either. To note, this is a $25 Harbor Freight test so the numbers could be weak from that.

          I did a dry and wet run, here are the numbers.
          Dry: 125/135/145/145
          Wet: 145/150/150/150

          Thoughts? Cylinder 1 is not 100% great, especially on the dry test.

          Comment


            #6
            Originally posted by bmwman91 View Post

            If the timing is good, maybe verify that the coil packs are wired properly and connected to the correct plugs?
            I want to verify a few things...

            The order should be the following, correct?
            Cyl 1 - Coil 3
            Cyl 2 - Coil 2
            Cyl 3 - Coil 1
            Cyl 4 - Coil 4

            edit: Im using coil on plugs and matched the plugs by the following diagram

            Last edited by jaredmac11; 05-06-2018, 07:23 PM.

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              #7
              I guess it was the coil order. I read some other threads that said they follow the order of the cylinders, 1-2-3-4 and it fired right up.

              I think the piston ring on one is going to be a problem but Im going to enjoy the car for now.

              Comment


                #8
                I tried 1-2-3-4 and the order was off. That diagram above shows cylinder number, not firing order. I was running wasted spark so I still got cylinder 1 and 4 to fire and was running on 2 cylinders, able to idle sort of. After I looked at it, I rewired to match the correct firing order which should be 1342. That fixed it and i could drive it on megasquirt

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                  #9
                  Were you running spark cables to the coil packs or Coil on Plugs?

                  It was 11PM and I have an open exhaust so I didnt run it long, but it started right up with 1-2-3-4.

                  I'd like to get to the bottom of this-- I see a ton of conflicting orders when I tried researching this the very first time. Something tells me it would run like dog crap if the order was off by even 1 plug, let-alone 2 or 3

                  Comment


                    #10
                    #1-4 in the diagram refers to #1-4 cylinders (front-to-firewall). That is for the wiring as you have found. Firing order in the ECU will be 1-3-4-2, as is the case with almost every I4 engine.

                    And yes, if you mix up one connection, well, that means that you messed up at least TWO since there are only 4 connections. It would either not run at all or run so poorly that you would know instantly.

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                      #11
                      Originally posted by jaredmac11 View Post
                      Were you running spark cables to the coil packs or Coil on Plugs?

                      It was 11PM and I have an open exhaust so I didnt run it long, but it started right up with 1-2-3-4.

                      I'd like to get to the bottom of this-- I see a ton of conflicting orders when I tried researching this the very first time. Something tells me it would run like dog crap if the order was off by even 1 plug, let-alone 2 or 3
                      I was running coil on plug. I also was running standalone ecu. If you are running a 91 ecu (175 iirc) then it should just plug and play.

                      I would check tdc, make sure cam gears arrows are pointing up and I hear there is a tdc lock on the back of the crank so I would check the crank and cam are both at TDC.

                      Coil 1 should go to cyl 1, thats probably part of the problem.

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