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Odd ball application.

Discussion in 'FAST Support Forum' started by robfrey, Mar 13, 2018.

  1. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    I am trying to run a FAST XFI on a turbo charged 292 in line Chevrolet motor.
    Nobody makes a dual sync distributor for this application. I was able to mount a discrete cam sensor and trigger off A magnet that I installed in the cam gear. I am also trying to run a MSD Pro Billet distributor and get the crank signal for the inductive crank pick-up from it. I understand that if I can not get signal ahead of cylinder firing, I can not have the XFI control the timing. As luck would have it, I was able to disconnect the vacuum advance can, then rotate the pickup in the housing so that the XFI would see the signal approx 50 degrees before top dead center, then of course lock the pickup in place. I thought this would work as the pick-up moved independently of the rotor position so the rotor phasing is correct. The problem is that the ECU is just not seeing the crank signal (no indicator light). I ohmed out the pick-up and checked the air gap and both are near center of MSD specs.
    Any ideas beside building some sort of custom crank sensor?
     
  2. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    I will try to put it on the oscilloscope when I get a chance and post a pic of the signal.
    What is the minimum voltage rise that I need to see a trigger?
     
  3. Fastmanefi

    Fastmanefi Active Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    Did you disable the discrete crank input? Inductive signals have a polarity as well. Only a scope would tell you that. You need at least .4 volts at cranking RPM.
     

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  4. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    By disabling do you mean grounding the digital input, then yes.
     
  5. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    At 200 rpm (100 distributor shaft speed)
    [​IMG]
     
    Last edited: Mar 13, 2018
  6. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    I grounded the discreet crank input Brown and white wire from pin A8, correct?
     
  7. Fastmanefi

    Fastmanefi Active Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    Yes. The Brn/Wht to the Blk/Wht. Signal looks ok. The Crank LED should blink assuming the ECU has power.
     
  8. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    I grounded it directly to battery ground.
    Let me change it around in the morning and try again.
    I think there may have been a wiring error. We may have for a split second put 12v+ through the sensor ground.
    It went though a relay coil first. It still would have 12v but low amp. I can confirm if this happened in the morning also.
    Any other test I can run?
     
  9. Fastmanefi

    Fastmanefi Active Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    You should not disable by tying to battery ground. Sensor ground is different. Look at the schematic and you'll see the difference. 12V to the sensor ground would smoke the ECU because the sensor ground goes through electronics.
     
  10. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    I did not put 12v+ through sensor ground like a thought we may have.
    Also, the brown and white discreet crank sensor wire was grounded to sensor ground but not crank sensor ground.
    It was grounded to the black wire with white stripe. Is that ok?
     
  11. Fastmanefi

    Fastmanefi Active Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
  12. robfrey

    robfrey New Member

    Joined:
    May 5, 2010
    Problem traced to bad ecu.
    Never found any wiring issues and it was a new XFI unit (bought 9 years ago) so I’m not sure why it did not work. Crank sensing seems to be the only thing not working.
    Swapped in another ecu and it worked.
     
  13. Fastmanefi

    Fastmanefi Active Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA

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