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    M50b28 intermittent issues

    I have an OBD1 converted M52B28 in my e30, and it runs great most of the time...however...

    When I start the car every now and then it smells like fuel but idles fine. I have no cats but this is a new occurrence as of two days ago. Coolant temp sensor is a brand new bosch unit.

    Once it hits operating temperature, if I am moving and either push the clutch pedal in or put it in neutral when coasting to a stop the idle surges from about 500-1000. Once I come to a complete stop, however, it recovers and settles where it should be. Only when I'm coasting at operating temp does it do this.

    Lastly, its down on power sometimes. One time I'll accelerate to full throttle in first gear and it will spin like crazy, slam second and it walks sideways, other times I'll get on it and it runs smooth but seems way down on power to the point it won't spin at all...hell it won't even chirp second.

    All vacuum lines and gaskets are new. I am throwing a code for MAF and O2 even though I've tried three different MAFs and two o2 sensors.

    There's no vac leaks from what I can tell. When its cold its fine...all this is only once it hits operating temp, except for the fuel smell issue which just started the other day.



    The thing that gets me the most about this is this started happening and has progressively gotten worse. When I first finished the swap it ran great all the time...but this is becoming more common of an issue with it. Sometimes when I hit vanos it bucks even...not all the time, but sometimes. And high RPM in 4th it falls on its face, I get more pull shifting to 5th and accelerating. I have 3.91 gears so that's normal highway speed there.

    And if you drive the car lightly, like a normal person, you can drive it all over and it will never act up. Its only under hard throttle.


    Thoughts, opinions?

    As I said, it is an M52B28 with M50 intake, harness, sensors, and 413 DME, no tune.

    BTW, I'm still getting an average of about 23-25mpg with it running like this, so, idk.

    #2
    I've got a similar thing down to a T. Been diagnosed as my TRM chip but they're telling me nothing of use.
    1989 Carbon Black 328is

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      #3
      i had something like this but quite a bit more severe. i had a TRM tune as well and that's what my problem was. before looking into more tunes i would go back through to make sure your wiring is still all correct and your ground are good. throwing maf and o2 codes could be leading to fuel issues and that could lead to why it's losing power. check out your fuel pressure when it gets to operating temp and make sure those numbers check out as well.
      If you're not going to do it right, please don't take it out on your car!

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        #4
        I'm still untuned running the stock m50b25 chip, but as I said, it's a problem that has been getting worse, which if it was a tune I'd think it would have been that way from the beginning.

        But fuel pressure didn't cross my mind though both pumps are new. But the inline pump is audible.

        Comment


          #5
          Maybe you need a tune?


          Sent from my iPhone using Tapatalk

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            #6
            Originally posted by E30335i View Post
            Maybe you need a tune?


            Sent from my iPhone using Tapatalk
            Then why would it have ran great then been getting worse over time, but still runs great most of the time? Doesn't seem like a lack of tune would cause that.

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              #7
              Okay but at the initial start your car was learning and now it's compensating for now. Either that or it's like this. You have maf and o2's. That can mean a vacuum leak unheard to the ear. Un metered air coming in. Lean code. But if you have rich then your car is dumping too much fuel. That's just basic diagnostics. I'm not too familiar specifically to your build but if I get schooled I'm glad I'm learning


              Sent from my iPhone using Tapatalk

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                #8
                Originally posted by E30335i View Post
                Okay but at the initial start your car was learning and now it's compensating for now. Either that or it's like this. You have maf and o2's. That can mean a vacuum leak unheard to the ear. Un metered air coming in. Lean code. But if you have rich then your car is dumping too much fuel. That's just basic diagnostics. I'm not too familiar specifically to your build but if I get schooled I'm glad I'm learning


                Sent from my iPhone using Tapatalk
                I've disconnected the battery so it can relearn and no difference there either.

                But that was my thought was a vacuum leak but I cannot find anything. I don't have a smoke machine, but the old brake cleaner trick doesn't show me anything.

                Idk.

                Needs a clutch now though.

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