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Slight misfire thru rpm range

Discussion in 'FAST Support Forum' started by fishhore, Apr 17, 2018.

  1. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Note: You may not need or want the added vacuum degrees. But, vacuum timing will help fuel mileage where it can be added, and it will sometimes alleviate steady pedal part throttle rpm hunting. GM only added 6-7 degree vacuum canisters to their 10:1 compression engines back in the day - and these were corporate settings.
     
  2. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    So I’m at 16* initial, total 34*. I checked my “ported” fitting with my vac gauge and it’s showing manifold vacuum so I’m leaving vacuum advance plugged for now. I’m showing 15 on the vacuum gauge at idle, I could get it up to almost 17 steady needle but timing was at 28* so I just set total to 34* and let initial fall at 16*. Reset tune, left a/f ratios at 13.5 and 14.0 for now. Car drives amazing and is much mellower and drops right down to idle without hunting for it or dipping. Big difference with this dizzy upgrade. But. I’m still hearing a very subtle blip out the exhaust while at cruise in all gears. At 60mph and tps sensor around 5-6% cruising I can’t hear it but the road noise may be covering it up. It’s the same noise as before just much much more subtle now. I ran a/f up to 14.5 cruise for a few miles but it was worse there.
     
  3. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Another thing I noticed which may or may not matter is my tps volts at wot are 3.8. Is this normal?
     
  4. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    You may need to reset the TPS - watch the IAC and keep it at 20 (fully warmed engine). Bring your initial up 2 degrees to 18 and try it with the total at 36. You may be able to reach 20 initial with a mechanical total of 38 - just don't go higher than 38. At least you are now at the minimum recommended FAST initial of 16. When you make changes in A/F, only make them a tenth at a time. Too much at a time confuses the computer map building. All the maps in the range need time to correct for new settings.
     
    Last edited: May 16, 2018
  5. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Reset tps after adjusting iac today. And then reset again during computer restart. Should I see full volts thru tps ?
     
  6. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Just what showed as full when you were setting the TPS with the throttle opened wide..
     
  7. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Ok just making sure 3.8v at wot is ok
     
  8. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I may have to send computer to fast for them to test. That’s the only thing that hasn’t been altered or swapped out yet
     
  9. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    3.8-3.9 sounds good at WOT.
     
  10. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I’m gonna just let the computer learn for the next 100-200 miles and see how it goes. I’ll send in the computer and monitor after that. The way it all runs besides this little puff out the exhaust at cruise I get makes me positive everything is fine but it’s worth having them check the computer if it doesn’t clean up after some learning
     
  11. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    You need to finish working on the timing first before sending in the computer.
     
  12. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I just may have found a problem. I bought a tanks inc efi fuel tank and pump in tank set up and just hooked up the pump positive to the red wire labeled pump positive coming out of my Ez Efi loom. And then just grounded the pump. Looking through the instructions again I notice something about using a relay.
     
  13. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    The red wire cones off the FAST fuel pump relay in the harness. That isn't a problem. A quick check for the relay is to listen to the pump when you turn the key on. It will cut off after a few seconds if the engine isn't started. You still need to find your optimum timing and add in the correct vacuum timing.
     

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