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Electric fans causing voltage drop and stalling megasquirt

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    Electric fans causing voltage drop and stalling megasquirt

    I am currently running a 16" spal fan on the radiator and a 14" chinese special fan on the ac condenser. I started with just the 14" wired into the stock power and ground except I bypassed the temp sensor in the rad so it was always powered and i cut the ground to the relays in the fuse box and ran that back to the megasquirt. with this set up I had no issues except the car ran a little hotter than it had with the OEM aux fan.(big surprise). I added the spal fan to try to help with the cooling and just added that to the same aux fan wiring and they are triggered by the same ground to megasquirt. It was running fine like this for a while.
    Recently I got a stereo system for the car and I figured with the added aux fans and the stereo I was putting a lot on the alternator so I upgraded to the larger alternator from the 750il(i think). since this 'upgrade' I noticed when the fans cut on i see the voltage drop from 13.7-13.5 to 13-12.8. this drop is there if I'm driving or idling. when I'm idleing sometimes this causes the idle to stumble and sometimes the car stalls. I turned up the idle voltage compensation and it got better but sometimes it doesnt catch.
    Also, sometimes when I'm driving the car cuts off when I'm cruising. There is no sync loss, and the rpms slowly drop as im slowing down and the car always fires right back up. it feels almost like fuel overun kicking on or like my spark coils are loosing power. once i was going down hill and kept it in gear and pumped the throttle and it wouldnt come back till i cycled the ignition off and on...then it was right back on. of course this problem is intermittent and I havent been able to get a data lot of it on the road...every time im out logging it drives fine. then when I have my gf in the car and we are going somewhere it cuts of 2-3 times. I have logged it cutting off in the drive way and idling and all sensors look good...its just like someone cut the power to the ignitnon coils.

    Am i maybe overpowering the ground wire from the fan relays to the Megasquirt? Maybe I should suspect the alternator i swapped in? (it was in my old e30 with a stereo with no issues)
    Could this be interfering with my coils?
    My last guess is I have some kind of wiring short somewhere?

    any thoughts would be appreciated.

    #2
    I just looked up a data log from before the alt upgrade and the voltage drop was greater with the smaller alt. from 13.1 off to 12.5 when the fan came on. I'm guessing that while the voltage drop is too much, it's probably not the cause of the random stalling.

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      #3
      Are you sure the voltage is correct in megasquirt? Mine is pretty wrong (shows 12v, and its got a proper connection so it should be 13 like the battery has on it), i believe there is a calibration you can do.

      Why not put it back to OEM mech fan? My M20 has no issues keeping cool here in Australia with only the mechanical fan on the front of the engine.

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        #4
        I'm considering putting the oem fan back on...idk why but ever since i got my air conditioning working and replaced the aux fan last summer, the car struggled to keep cool unless i was moving. I replaced the fan clutch, rad, tstat, etc first and it didnt help so i went with the spal fan which handled it. maybe the parallel flow condensor restricts airflow? this car is working toward a turbo and I'm gonna switch to a late model cooling setup next time i do a timing belt as this is an 87is. for this reason I'll need the electric fan to keep room for the intercooler. Just wondering if i should expect this much voltage drop.

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          #5
          How is the fan wired?

          what size is your alternator cable?

          what size is your ground?

          Zach@Zakspeed.us

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            #6
            I'm running a fairly large stereo setup with my electric fan and only had issues with my old volvo fan. The amperage draw was CRAZY with that thing, but it moved some serious air. I thought it was normal til I replaced it with a DEPO fan. (meant to order another genuine volvo and got duped instead.) Decided to just run the DEPO and couldn't believe how much less draw it had. This is on a turbo m42 and AC is still ice cold. I also get similar voltage's and drop numbers but it's only for about a second, then back to high 13's. I agree on checking grounds as well as health of current alternator and battery.
            ------------------------------------------------------
            1982 528e - Sold
            1987 325e - Totalled
            1990 325is - Sold
            1997 540i6 - Sold
            1991 325ic - Sold
            2013 335i - Sold
            2005 X5 - Daily
            1991 318is - *work in progress*

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              #7
              I just spliced the fan connector in place of the OEM aux fan connector. then i bypassed the rad temp sensor that would normally trigger the fan. the ground is triggered by one of megasquirts programmable outputs which is a ground. I cut the ground to the fan relay and connected that to the megasquirt ground. I believe that this ground triggers the relay so megasquirt doesnt see the large current draw but i could be wrong.
              I'm probably dealing with 5 different problems right now so It will be a combo of different things....I really think I might start planning on building a home made wiring harness for the entire car. a lot of my 30 year old wires seem so brittle and I always have electrical gremlins that seem to come and go. I can never get the problems to happen in the driveway, only when i'm far from home.

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