M42 Swap Crank No Start

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  • Claytr0n
    Noobie
    • May 2026
    • 2

    #1

    M42 Swap Crank No Start

    Hi everyone, after many hours of trying to diagnose my problem I've decided to ask for some help. I have an 84 323i that has been swapped to an M42 by a previous owner. It has run on the swap before but not since I have had it. When the engine is cranking over the fuel pump is not kicking on and there is no spark. Both the coils and the fuel pumps are getting power and the fuel pump runs when I jump the relay but they are not engaging when I try to start the car. My thought is that the ECU is not getting the timing information it needs from the crankshaft position sensor to trigger these systems and this is what I have tried in order to fix that:

    CPS from a running M42
    ECU from a running M42
    New main and fuel pump relays
    Checking all fuses
    Checking continuity between CPS and ECU, Fuel Pump Relay and ECU, Main Relay and ECU, Main Relay and Fuel Pump relay.

    I got a suggestion that it's possible the crank pulley slipped and now the cam position sensor and crank position sensor are feeding conflicting information to the ECU so this is what I am going to check next.

    If anyone else has other ideas for what might be wrong please let me know because I am starting to run out of ideas.
    Thanks in advance!
  • Claytr0n
    Noobie
    • May 2026
    • 2

    #2
    UPDATE: I checked the timing marks on the crank pulley and they lined up perfectly so now I am kind of stuck. I'll continue to do more research and update this thread if I find anything that fixes it.

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