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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
    You do, you just aren't noticing it with the driveline connected.
     
  2. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Ok iam going to start from scratch and not even trust where they put the timing tab. Will start over with the piston stop in number one cylinder and make sure tdc is correct then start from there.
     
  3. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    That's best. You need the mechanical initial (no vacuum) at about 16-20 degrees, slope at 4000, and a total mechanical advance of no more than 18 degrees. Afterwards, there may be some vacuum advance changes needed such as degrees and vacuum load %.

    You can't set the optimum F/A until the timing is corrected.
     
    Last edited: May 6, 2018
  4. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    So I set initial at 14 and ended up at 34 at close to 4000 rpm. No vacuum advance hooked up. Still a little rough through the rpm range in neutral. Lowered idle to 13.5 from 14.0 and cruise to 13.8 from 14.3. Almost instantly cleaned up my revs. Went for a little drive of only about 1 mile so computer really didn’t learn much but it’s already much better. Almost all of that slight miss I could hear is gone and the transition from cruise to Accel stumble is gone. Guessing it will get better as I drive it more. I was really focused on keeping those af ratios up not giving the engine what it wanted I guess. Will work more on timing in a couple days. But Could not get engine to ping/detonate putting load on the engine in 4th gear going about 25 up a slight hill.
     
  5. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    What's happening is your exhaust temp is staying higher than it should be (headers likely glowing due to the over rich A/F), and you might not be getting noticeable detonation, but you are getting pre-ignition. The higher exhaust temps will also get the plug wires and boots. Don't fool yourself. You need at least a 9 degree distributor (18 degrees mechanical advance) or less with a 4000 slope, that will allow a higher initial timing setting and a leaner fuel mix. The cap to rotor phasing may also be off. At 5000 RPM, you can bet this engine as it now will eventually self destruct. If you aren't smelling an over rich fuel smell from the pipes, something is wrong with the O2 sensor readings and/or the enrichment settings. The inside of your exhaust pipes should be light gray, not sooty black. The enrichment settings should be at zero during this process. If you haven't already reset the ECU with the Wizard, you should.
     
    Last edited: May 6, 2018
  6. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I did a ecu reset and put about 15 miles on the car just a little bit ago and it’s running better than it ever has. Did not have any fuel smell and just smelled my clothes and they don’t smell either? What is wrong with running the timing where it is for right now to diagnose? 14 initial with 34 all in isn’t going to hurt anything? It may not be optimal but they are safe numbers? o2 correction actually picked up fairly quickly with the new tune and was < +-4 or so most of the drive. All my enrichment settings are at 0
     
  7. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I also hit all my header tubes at the head with my temp gun within minutes of shutting off the car and none were abnormally warm? Ceramic headers but no excess heat
     
  8. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Somehow, your O2 readings are off. That's the only explanation - or you would have a noticeable fuel smell and overly hot exhaust header temps with those numbers. The tail pipes would also run sooty black. The timing will not be that bad in relaxed driving unless you run above 4000 rpm and the timing goes higher. What was the exhaust header temp? The timing still needs correction. Once corrected, you will be able to run the ported vacuum with the dist. vacuum canister, and this will improve mileage and drivability.

    13.5 is fat for an idle F/A.
     
    Last edited: May 7, 2018
  9. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Corner header pipes were all around 600-615* at idle and centers all around 630-650*
     
  10. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Temp gun aimed about 1” from flange at head
     
  11. A A

    A A Well-Known Member

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    Jun 22, 2014
    That sounds good and tends to again indicate something leaner than 13.5.
     
  12. fishhore

    fishhore Member

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    Aug 15, 2014
    I thought a leaner mixture could burn hotter?
     
  13. fishhore

    fishhore Member

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    Aug 15, 2014
    Or would overly rich burn out into the header?
     
  14. A A

    A A Well-Known Member

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    Jun 22, 2014
    Overly rich burns hotter in the header as more fuel burns outside the cylinder. Best power is made with higher initial timing and timing optimized with leaner mixtures that are not so lean as to burn pistons or valves.
     
    Last edited: May 8, 2018
  15. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Has anyone tried the hei dizzy that fast has?
     
  16. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    If you must run HEI, the MSD PN 8365/83653 would be a better choice. HEI (coil in cap) is not the best ignition solution. Personally, I would run the MSD 8361 or 8360 with a FAST E6 or MSD 6A ignition box and firewall or block mounted coil (E92 or Blaster) for them. All you'll need to do with the 8361 or 8360 is install the black advance bushing that comes with them. They come with the correct springs installed.
     
  17. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Ok I have a msd 6a now. But my dizzy is just a cheap Chinese billet that came on the engine. Looking to upgrade.
     
  18. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    A FAST E92 coil or the blue MSD HVC Blaster coil with the MSD 8161 Pro Billet distributor would be a nice upgrade and will compliment your EZ EFI 1.0 and MSD 6A very well. The round MSD Blaster coils can also be used but must be mounted vertical.
     
    Last edited: May 11, 2018
  19. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    What is the tps sensor voltage supposed to be at idle? I swear it’s always .2 but has been showing .3 the last few drives. Have re calibrated it with no change. Car was running great and now It’s acting like it’s cutting out during throttle transitions? Like a fuel related issue
     
    Last edited: May 12, 2018
  20. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Check for sticking throttle blades (the rear blades should be lightly closed) and reset the IAC and TPS. Idle should be set for 750 - IAC at 20. Once you have a new distributor that allows more initial timing, all of this will need resetting again.
     

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