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    #1

    Cold accelerating weirdness

    This is a strange one. My sons 89 325i seems to have developed a weird problem during hard acceleration when the car is not yet up to temp. If you push the go pedal to the floor and let the rpm's get in the upper range the car will suddenly lurch for a split second and then continue on as if there was nothing wrong. When this happens the CEL will flash on for as long as the car seems to be electrically dead. This only happens on a cold engine and gets really noticeable with the AC on. When the compressor first kicks in that extra load seems to make the engine halt for that split second until the engine is fully warmed up. With the AC on though it will do this at lower rpms too.

    I am thinking maybe the AFM is bogus at full throttle, but that doesn't explain why it would happen with the AC on and at lower rpm's. Also suspecting maybe the crank sensor is on its way out as this seems to be a definite electrical problem. A fuel problem would not cause the engine to stop running for only a split second IMO, especially because I can hear the fuel pump running and even if the fuel pump cut out for that split second the rail and injectors would have fuel and pressure still during the time it fails.

    Also could be a bad main relay too I guess, but that doesn't make much sense to me either. If it was the relay then the car wouldn't start to begin with and the fuel pump wouldn't work.

    The car runs fine otherwise and idles great as well. Sometimes is hard to start the warm motor and I suspect maybe some slight injector leaking as the cause of that problem as it will fire right up if you push the go pedal down a bit while cranking. Any thoughts on the subject would be greatly appreciated. It is hard to describe such a peculiar issue, but I hope someone will have enough info to help me figure this out. Thanks as always!
    The difference between porcupines and BMWs is that porcupines have the pricks on the outside!
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    #2
    No suggestions?
    The difference between porcupines and BMWs is that porcupines have the pricks on the outside!

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      #3
      Maybe try not going WOT when the engine is cold? I mean, regardless of how it sounds like it's running rich you shouldn't be beating on it when cold.

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        #4
        I generally don't go WOT on a cold engine, but the car does this with the AC on and when the clutch kicks in on the compressor the car kills momentarily under that extra load until the motor is completely warmed up. I thought it was a strange thing for the car to do and tried to isolate the condition. It didn't do it under normal accelerating conditions with the ac off. I could only get it to replicate at high rpm on a cold engine. This is why I said the problem was at WOT at high rpm on cold motor, not because I am abusing the car, but because that is when it cuts out and does the same thing with the AC on at lower rpms. I am trying to figure out the underlying problem without the AC being a factor.
        The difference between porcupines and BMWs is that porcupines have the pricks on the outside!

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          #5
          i doubt it's the CPS - if it was you'd be having weird issues while warm with the AC off too. probably rules out a vacuum leak too.

          my bets are on excess fuel while cold. do you have access to a wideband you can borrow to help with testing? try pulling the spark plugs to see how they look if you don't. speaking of them, how old is the ignition system? because my guess is that this is a real simple fix. spark plugs, wires, cap, FPR or something like that

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            #6
            Spark plug wires have a lot of miles, but everything else was replaced when I did the timing belt a little while ago. Maybe the coil?

            Why would you think this is an excess fuel problem? The car is cutting out, not back firing.

            No wideband for testing either.
            The difference between porcupines and BMWs is that porcupines have the pricks on the outside!

            Comment

              #7
              backfiring isn't necessarily a symptom of excess fuel, but it certainly can be under the right circumstances. reason i say it sounds like excess fuel is that if you had a lean issue it most likely wouldn't only happen while the car was cold - it'd be all the time.

              if you think it might be the spark plug wires arcing out onto the valve cover or something, try this - take a mister/spray bottle, fill it with water and spray it on the spark plug wires/cap/coil while the car's running. if the insulation is poor on any of these the engine will start misfiring

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