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Microsquirt VR signal lost around 4,800 RPM

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    Microsquirt VR signal lost around 4,800 RPM

    Started tuning my DedericMS plug and play MS2 yesterday, and ran into an issue with losing the VR signal around 4,800 RPM. The VR signal looks clean otherwise, but I still need to get a timing light on the car to make sure the tooth #1 angle is perfect. When reaching 4,800, it's like fuel cut/redline, and the lost sync counter does go up.

    The Dederic box is Microsquirt v2.2 based, running MS2/extra firmware. He ships the board with a 10k ohm resistor on the VR+ (pin 47). DIYAutotune's PNP kit is also Microsquirt based, and they supply their kit with an 18k resistor. In other documentation, they mention a 10-20k resistor depending on the application. For reference, MS2 boards come with a variable potentiometer for the VR signal, so they are able to fine tune it using the pot.

    I tried wiggling the CPS bracket on the motor, but there is not much play there. The air gap is minimal. I pushed it as close to the toothed wheel as possible, but didn't try going the opposite direction (as far as possible from the wheel).

    Should I just try the 18k resistor? Or even possibly using the proto area on the daughter board to put a potentiometer like MS2 uses?

    EDIT: I just checked my air gap between the crank wheel and the CPS. It's very tight, probably about 0.3-0.4mm. I am going to try and back it off to the 1.0mm spec this weekend before changing anything on the MS board.
    Last edited by Digitalwave; 12-21-2017, 10:50 AM.

    #2
    im having the same problem, car ran verywell rebuilt my motor now im getting a sync loss at around 2500. what was your solution.
    sigpic
    86 325e now 327iturbo hx35 ms2
    DRIFT CAR
    warped my mamifold sell me your RSI MANIFOLD

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      #3
      Haven't fixed it yet (busy with the holidays). I will report back when I do.

      In the mean time you should:

      1) Check the resistance on your TPS. Disconnect it from the wiring harness, it's the connector closest to the driver's fender next to the diagnostic port. Pins 1 and 2 of that connector should have 540ohms of resistance, +/- 10%.

      2) Check the air gap on your CPS to the crank wheel. The spec is 1.0mm +/- 0.3mm. Mine was way too close, but moving it back didn't change anything. I've seen people report that moving theirs closer helped, but I wouldn't count on it.

      3) Determine what, if any, resistor you have on the VR signal. Mine had a 10k ohm. I am trying 12k, then 15k, then 18k next. From what I can tell, the resistor will typically solve the issue. It can definitely depend from car to car. Recommended in the 10k to 20k ohm range. You want it "just right," because if you go too far, the car will go to redline, but you won't have a strong enough signal when cranking the car.

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        #4
        I had this same issue with my car on MS for a long time - losing signal right before 5k. It was fine on the stock 173 ecu.
        Everything checked out, but I was convinced it was the CPS still and it turned out to be so.

        The car would rev freely to 7k if I pushed the CPS closer to the wheel with my thumb while a friend revved the engine. My CPS was 6 months old, but aftermarket.
        A genuine HELLA CPS fixed the issue. The difference in quality is apparent side by side.

        1991 325iS turbo

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          #5
          I am using an OEM Hella CPS (metal) and it tested out okay, but I know that doesn't mean it's "good." They are still available new from ECS for about $145. I'll order one next if the resistors don't fix my issue. After that, the next thing to replace would be the crank wheel/harmonic balancer.

          EDIT: I just now tested some different resistors. It didn't fix or alter the problem much. Going to order a new OEM CPS and try that next.
          Last edited by Digitalwave; 12-28-2017, 07:58 AM.

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            #6
            I feel like a broken record but, +1 for checking your cps gap...had me confounded for months. In MS2 there are 2 screw head potentiometers that you can adjust to correct the VR signal that are inside on the megasquirt board. From what I understand one is like a lower limit and the other is an upper limit for the VR signal. You may want to look into that.
            https://www.diyautotune.com/support/...megasquirt-vr/

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              #7
              Also, If any of you guys are near maple shade NJ, I'd be happy to take a look at your set up with you.

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                #8
                Originally posted by kyleconstantine View Post
                I feel like a broken record but, +1 for checking your cps gap...had me confounded for months. In MS2 there are 2 screw head potentiometers that you can adjust to correct the VR signal that are inside on the megasquirt board. From what I understand one is like a lower limit and the other is an upper limit for the VR signal. You may want to look into that.
                https://www.diyautotune.com/support/...megasquirt-vr/
                I did try my air gap as close as possible to the wheel as well as the largest possible gap. That didn't change anything, so I set it to the factory spec (1.0mm). My sensor looked like it had contacted the crank wheel at some point, so maybe that messed it up. I am installing a brand new OEM CPStoday or tomorrow to test next.

                MS2 does have two potentiometers for fine tuning the signal, but Microsquirt does not. Microsquirt (which is what I am using) uses a resistor (R26) on the VRIN+ pin.

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                  #9
                  Damn my reading comprehension is bad late night. I'm using microsquirt as well. It's a whodwho built unit. if the new cps doesn't solve your problem ill check out what size resistor he has installed in mine.

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                    #10
                    No worries! Mine is a blueapplesoda/Dederic. I think they both (blueapple and whodwho) used 10k resistors on their builds. I have a good feeling that the new CPS is going to fix my problem, but we will see soon.

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                      #11
                      Happy to report that the new OEM CPS fixed the issue 100%. I am back running the 10k resistor that came on my daughter board. Cranks and goes to redline no problem.

                      Comment


                        #12
                        Awesome to hear...it seems motronic is just not as picky as megasquirt when it comes to the vr signal.

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