Announcement

Collapse
No announcement yet.

Wiring Help

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Wiring Help

    I need help interpreting the wiring schematic here. I have most of it figured out, but I'm a little confused about the DB9 connector. The schematic shows the brown SPARK B wire going from the DB37 to the ICM, and then there's a yellow SPARK B wire coming from the DB9 to the ICM. How is this wire connected to the Megasquirt? I imagine this is the tach signal wire which was jumpered on the MS board, but I just want to make sure I'm not missing anything. Also, the picture is a bit unclear about the shielded twisted pair wire from the CPS which has a drain wire. I connected the drain wire to pin 2 and the black ground wire to pin 1. Is this correct?

    I plan on using the FIdle wire (PWM Idle wire from the harness) to power my aftermarket electric fan, so the only thing I have to add to this circuit is another 4-pin relay, right?
    I added boost control to the board with the spare transistor location (boost control kit bought from DIYAutoTune) and I chose DB37 pin 6 as my signal wire.

    I was thinking of including the knock sensor and oil pressure sensor into the system, but I'm not sure how it ties in with the harness/circuit board. Is it difficult to add these after wiring everything else?

  • #2
    By the looks of it, that is a 3.57 board. The two spark wires are to control the individual coils of the ICM. Originally the MS did not have the DB9, there were 3 LEDs on the side of the box to display rpm, fuel enrichment and I think power. On the 3.57 boards you can repurpose those LEDs to do what you want. It looks like one of them was repurposed to control a coil.

    The stock oil pressure senor is a simple on/off switch that trips at something stupid low around 3-5psi. If you plan to log oil pressure you will need a sensor that can read pressure and then run it through an an ADC circuit. You may have configure a separate gauge for this with a generic spare input.

    If you plan to use a knock sensor, you will need a knock box/add i card. Look it up on the MS forums and see if it is compatible with your version of MS.
    -6S Resident Mechanical Forensics member #001.
    1995 SC2 Turbo 3.6L DOHC, 6sp manual, Ford 8.8 rearend running on MS3x.
    1998 F-250 5.4L triton...stock.

    Comment


    • #3
      I'm going to start over, because I think I see where I am getting mixed up. My Megasquirt 2 does not have a DB15 (don't know why I was thinking DB9) and you are saying that it was added later, so my board is not a V3.57. So I have to add a circuit to one of the LED outputs to control the second coil of my ignition system and the yellow wire would be that output (which in my case would need to be wired to one of the spare wires on the DB37)? I was under the impression that the GM HEI (and by extension GM DIS) only needed one wire to the coil driver. I've been looking at both pages of the MSExtra manual and I'm no nearer to understanding than I was before.
      Last edited by Jooshmeister; 01-09-2020, 09:51 PM.

      Comment


      • #4
        The GM HEI will work on the OBD1 ignition system. The OBD2 system has the PCM controlling the coils individually, which would require two control circuits.
        If you have an OBD1 system make sure to install inline a 1/4 watt or more 10k ohm resistor between the MS and the ignition control module on the EST wire (sparking timing advance wire). If you don't install it you will get some weirdness in the higher RPMs that will cause misfires and a loss of power.
        -6S Resident Mechanical Forensics member #001.
        1995 SC2 Turbo 3.6L DOHC, 6sp manual, Ford 8.8 rearend running on MS3x.
        1998 F-250 5.4L triton...stock.

        Comment


        • #5
          Originally posted by S.Bretz View Post
          The GM HEI will work on the OBD1 ignition system. The OBD2 system has the PCM controlling the coils individually, which would require two control circuits.
          If you have an OBD1 system make sure to install inline a 1/4 watt or more 10k ohm resistor between the MS and the ignition control module on the EST wire (sparking timing advance wire). If you don't install it you will get some weirdness in the higher RPMs that will cause misfires and a loss of power.
          This is so confusing...

          So I've built my Megasquirt to have VR tach input and no ignition bypass circuit, so I have to add the bypass circuit and change the tach circuit to Hall/Opto to make it work with the OBD2 ICM? Why does the picture above show the crank position sensor wired directly to the Megasquirt instead of the ICM if that's the case? From what I understand, the sensor should be wired to the ICM and the ICM should output a Hall/Opto signal to pin 24 and I can exclude the shielded twisted-pair wire on pins 1, 2 and 24.
          Last edited by Jooshmeister; 01-20-2020, 02:35 PM.

          Comment

          Related Topics

          Collapse

          There are no results that meet this criteria.

          Working...
          X