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M52B28 Swap Running Issues

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    M52B28 Swap Running Issues

    Hello everyone,

    I just purchased a 1991 318is that has 100k mile M52B28 single VANOS swap. Car had been swapped about a year ago and hadn't had many miles put on it until I purchased it. Been driving the car and wrapping up a few swap related things that hadn't been done and noticed a few issues with how the engine runs.

    1) Noticed its has an intermittent hot start issue where it'll start up fine, run for a few seconds, then sputter and die. If I try again, it wont start, but if I wait about 30 seconds, it'll start and run fine with no issue. Only does this when the engine is hot and has never stalled after it has been started again. Car smells like gas when this happens, but the evap system is not hooked up currently (VTA right now under hood, intake vacuum line blocked off, getting that fixed soon), so the smell is most likely coming from that.

    2) It backfires a ton when I left the off throttle, at any RPM, driving or in neutral. The backfires are very loud and consistent too, both when the engine is cold or hot. It doesn't have any catalytic converters, but I feel it shouldn't have that much overrun.

    3) Noticed that it doesn't have much power above 1/2 throttle. Below 1/2 is feels great, no hesitation, tons of power. But above 1/2, it feels like it should have more.

    Pulled codes from the ECU and its throwing codes for the evap, secondary air injection system (deleted), and secondary O2 sensors (also deleted). I don't think this ECU has been re-flashed by the previous owner. Is a re-flash required for a swap, causing the issues I'm seeing?

    I understand it could be multiple things causing issues like this (vacuum leaks, fuel pump, fuel filter, cam/crank position sensor, etc.) but where should I start?