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S52 OBD2 Swap - Spark + Fuel, Crank No Start.

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    S52 OBD2 Swap - Spark + Fuel, Crank No Start.

    Hey guys,

    Happy new year!

    I am trying to get my project running. For last 2 months I have been stuck with it not wanting to run and idle . I am keeping the OBD2 setup and a DME was purchased with EWS deleted. I am using a S52 swap wiring harness adapter.

    I have checked multiple times the essentials to get the car at least running. The spark is strong, fuel feed and return hoses are hooked up properly.

    The engine will crank, hesitates to start but wouldn't. It will sometimes throw a back fire out from the throttle body.

    I tried spraying brake cleaner on the throttle body, just to give it a jump, and it would fire up for a second, and then dies off immediately.

    I have a few reasons that might cause this, but I still want to get some confirmation and insight before continuing the diagnostics.

    1. DME / ECU is malfunctioning.

    2. Timing is wrong, thus creating a backfire coming out from the throttle body.

    3. Cam or crank position sensor is bad, preventing the engine from starting.

    4. There is one ground that is not hooked up (pictures attached below), let me quickly explain why:

    I have previously attached that black ground to chassis and it sparked, so it must be a negative coming from the battery side.

    The reason I didn't attach it back is because I really don't know where does it go!

    This short video I took will show you which cable I am talking about: https://youtu.be/AiQeSLXx1Xs

    I taped the cable in red color tape so it wouldn't touch the chassis by mistake and start a fire.


    If anyone has experienced something similar to this or have some knowledge to share I would greatly appreciate it! I will actually send you beer money if your suggestion works

    Thank you for taking the time to help me out as this is my first time doing any swap and I am not in the mechanics field at all. I am not afraid to make mistakes, as long as I learn from them


    Click image for larger version

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    #2
    That cable looks to be the original positive +12V wire that supplies power to the starter on the M20. You must have run another power wire to your S52 starter?

    That cable junction you have in your hands (in the video) is the +12V junction that is supplied by the battery in the trunk - follow the big black wire that runs through the firewall to the truck. If you have hooked up grounds to this junction block you will have all sorts of issues....

    Comment


      #3
      ^ what he said. On m20 cars there is a grounding lug on the passenger side shock tower. As far as timing goes, did you mess with the vanos or anything? Only other way to mess up the timing is if you use the wrong crank balancer from a non vanos. I assume all the sensors are obd2.

      If you pull the valve cover off, it's rather easy to make sure your timing is correct enough to start. It will run with the vanos installed a tooth off.....



      Comment


        #4
        Before getting all diagnostic-tear-down, have you verified the injectors are actually pulsing? Fuel pressure on the lines won't matter much if the injectors are not energizing. Pull up the fuel rail, leaving the injectors, harness and fuel lines attached, bump the starter and see if there's fuel coming out of the important end of the injectors.

        Seeing it started on ether, I would lean towards the injectors being stuck or not being energized at all.

        Since you have spark, I am leaning towards the crank and cam sensors doing their jobs, and the wiring to be near correct.

        The black cable used to be the m20 starter/alternator junction. Since the PO tied into the stock e30 battery block, it's just a loose end. Can attach it to the starter on the outside large terminal if you don't want to cut it out.
        Last edited by ForcedFirebird; 01-04-2021, 03:32 PM.
        john@m20guru.com
        Links:
        Transaction feedback: Here, here and here. Thanks :D

        Comment


          #5
          Originally posted by ForcedFirebird View Post
          Before getting all diagnostic-tear-down, have you verified the injectors are actually pulsing? Fuel pressure on the lines won't matter much if the injectors are not energizing. Pull up the fuel rail, leaving the injectors, harness and fuel lines attached, bump the starter and see if there's fuel coming out of the important end of the injectors.

          Seeing it started on ether, I would lean towards the injectors being stuck or not being energized at all.

          Since you have spark, I am leaning towards the crank and cam sensors doing their jobs, and the wiring to be near correct.

          The black cable used to be the m20 starter/alternator junction. Since the PO tied into the stock e30 battery block, it's just a loose end. Can attach it to the starter on the outside large terminal if you don't want to cut it out.
          That's my thinking as well. Except that since it must be all injectors not firing therefore no power to the Injector rail?

          What do spark plugs look like? wet at all?

          Comment


            #6
            You can take a prybar and place one end on the injector and the other to your ear. You will hear an audible click if they are firing. But that doesn't necessarily show as much as a visual like John said. Keep an extinguisher near by!



            Comment


              #7
              Thank you guys for all the tips. I will keep working on the car and keep updating here if I find the issue.

              Comment


                #8
                Originally posted by ZekeTheSneak View Post
                You can take a prybar and place one end on the injector and the other to your ear. You will hear an audible click if they are firing. But that doesn't necessarily show as much as a visual like John said. Keep an extinguisher near by!
                Right. I've had them "click" but either have a very bad spray pattern, barely spray at all, and even some that steadily dripped with rail pressure.
                john@m20guru.com
                Links:
                Transaction feedback: Here, here and here. Thanks :D

                Comment


                  #9
                  Update:

                  The engine started :) Thank you guys for the awesome help!

                  The problem was the with the fuel pressure regulator (Huge thanks to Blake for suggesting that!)

                  Fuel was not being regulated (not pressurized) into the cylinder hence chocking the engine and not allowing it to start.
                  That also explains why there was fire coming out from the throttle body.

                  I have used the a 97 528i M52 fuel rail that has a built in fuel pressure regulator and bolts right up to the S52 OBD2 intake.

                  The engine didn't run at first couple of tries after putting in the new rail. But the crank seemed much more healthier than before, so I tried again and boom! it started :)

                  Hope this thread helps someone in the future.

                  Thank you again for everyone that helped :)




                  Comment

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