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E30 - M62 Charging Issue

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    E30 - M62 Charging Issue

    Hello everyone, I have a recent charging issue with my e30...it is an 87 ETA with an OBD1 converted M62B44 with a brand new Bosch 140amp alternator and a new Napa AGM battery.

    First off, the battery light in the cluster does illuminate and extinguish on startup. While the battery is discharging, the light does not illuminate, however.

    At idle at startup with no accessories on, it will sit at 13.6v. When the electric fan kicks on, it will drop to about 13v...if I turn the A/C and wipers on, and hit the brake pedal, it will discharge down to 9v to the point the wipers won't operate and the engine wants to stall. If I rev it up, it will rise to about 11v with all of these accessories on.

    If there is no excessive load, the charge will rise to 14v without issue. I just don't see how a 140amp alternator can have this much of an issue with a car that came with a much lower amperage one.

    I replaced the alternator through FCP's warranty thinking that was the issue, however, there was no change. The old one and this one tested good. The battery was replaced as well. Again, no change. I also tried a spare DME with no change there either.


    My last thought is the gauge cluster. I am going to try another, however, I am confused as the battery light does illuminate on startup as it should...however, it does not illuminate when the voltage drops, which I find odd. Also, it charges sometimes...so that is odd.


    I'm just looking for any experience or ideas where else to look. I did the M62 swap about 5 years ago and haven't had an issue with it until recently with this, and I'm pulling my hair out trying to figure out if its swap related or somewhere in the body. Also, is it normal for the brake lights to create such a large voltage drop?



    TL:DR - 87 E30 - OBD1 M62B44 swap - 140amp alternator is unable to keep up with stock e30 electrical demand. Alternator and battery confirmed functional. Battery light turns on and off at startup but does not illuminate when voltage drops below 12v. Any incite?

    #2
    Generic advice, but how about a ground issue, maybe one that's corroded and high impedance?

    Also, look back at recent maintenance, and consider what may have been moved, bumped, unhooked or jiggled.

    Comment


      #3
      Check your positive terminal connections. Remove them and clean them with a wire brush

      Comment


        #4
        I just went through the ringer with my m6x alternator. Ended up going through 3 of them and two batteries before finally determining it was just a function of the way I wired the engine swap. I was seeing ~12.3v with the lights and blower on at idle (I don't have A/C). The power windows barely worked at that voltage.

        With an e34, there is two idle bumps. One for headlights, one for A/C. The DME has inputs for both signals. Each one bumps the idle up maybe 50 RPM, not even a noticeable amount unless you really pay attention. I wired one of those DME inputs up to switched 12v, and now I sit at 13+v at idle regardless of what is running, and the power windows are faster than they've ever been.

        My thread where I sorted it out:

        https://www.r3vlimited.com/board/for...mething-for-me
        85 325e m60b44 6 speed / 89 535i
        e30 restoration and V8 swap
        24 Hours of Lemons e30 build

        Comment


          #5
          The grounds have been cleaned and checked, and the battery terminals cleaned...I forgot to mention those, but, those were the first steps! Lol.


          Originally posted by JGood View Post
          I just went through the ringer with my m6x alternator. Ended up going through 3 of them and two batteries before finally determining it was just a function of the way I wired the engine swap. I was seeing ~12.3v with the lights and blower on at idle (I don't have A/C). The power windows barely worked at that voltage.

          With an e34, there is two idle bumps. One for headlights, one for A/C. The DME has inputs for both signals. Each one bumps the idle up maybe 50 RPM, not even a noticeable amount unless you really pay attention. I wired one of those DME inputs up to switched 12v, and now I sit at 13+v at idle regardless of what is running, and the power windows are faster than they've ever been.

          My thread where I sorted it out:

          https://www.r3vlimited.com/board/for...mething-for-me

          Thanks Justin! I will definitely check into wiring that up. I may run the signal from the electric fan switch 12v to that pin on the DME. My issue, though, is that even with accessories on, sometimes the alternator still cannot keep up, regardless of RPM.

          In Florida its common to have the A/C, headlights, and wipers on at the same time while stopped at a red light. In that scenario, it will drop to 9v. I can rev it up to 4k and it won't go above 11v. That doesn't seem right to me at all...as I'm sure the E34 had a lot more electronics going on at idle. I had this issue with two alternators so far.

          Here's two videos I took.

          A/C, Brakes, Headlights on:

          https://photos.app.goo.gl/GXpQtWBoegRMDVdT8


          Everything I could turn on (that's 9v...the decimal is very small, revved up to about 3k RPM):

          https://photos.app.goo.gl/B4NAK1R2nR3MPLJMA

          Comment


            #6
            Update on this...

            I'm having voltage drop between the battery and the cable at the front of the car.

            13.1 at the battery, 11.8 at the cable on the firewall.

            Tried two gauge clusters and went ham cleaning terminals... no difference.

            I will be doing more testing on Monday.

            Comment


              #7
              Time for a new shell I think...

              instagram: @tonerrrr
              High resolution E30 Fuse Box 300dpi PNG

              Comment


                #8
                Originally posted by tonerrrr View Post
                Time for a new shell I think...
                Go fix your M3

                Comment


                  #9
                  Are you doing an actual Voltage drop test? ( positive lead of your meter to Battery positive and negative lead of your meter to the front positive “jump” post ) The measurements you posted suggest your doing an available voltage test. Regardless, that’s a 1.3v drop which is still not good. Do the same test that I described from the battery to the positive of the alternator itself. That will tell you exactly how much voltage is being lost between the two. ( hopefully still 1.3v )

                  After that works your way backwards from there on your big red cable. It’s possible that your actual power cable has some high resistance in it ( corrosion or pinched against something ). Report your findings back here and I’ll try and keep helping :)

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