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  • ZZ6 target idle

    1970 Chevelle, ZZ6 crate motor, man. trans. w/ac
    The original problem was stalling when the clutch was pushed while de-accelerating with the AC on,
    The target idle was at 750 and the IAC at 7% with the engine warm. When I attempt to increase the speed via idle target change (engine warm, TPS at zero and green check mark on) no idle speed change occurs. When the ac is on the idle slows and does not return to the 750 the ecm shows. I have managed to improve the stalling by increasing the minimum idle learn rpm which seems to stop it from drooping so far that it stalls but don't understand why the ECM will not bring the idle up when the target speed is increased.

  • #2
    Keep Target idle speed at 750.
    To raise idle to desired RPM, turn idle screw Clockwise on throttle body.

    Then, after the idle screw adjustment, Power-cycle ign off, for 15secs, then on to verify throttle #value is at zero.
    if not at zero then, try a few more times.



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    • #3
      My car idles at 850. This is also a little more voltage to run the fans when they turn on.

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      • #4
        Sorry for the delayed response. the car is 45 min. away. I reset the idle with the screw and it runs fine, no stalling so I could just leave it as is. As I suspected the IAC is now at zero and (hot) idle is totally controlled by the throttle plate position. So I still am curious as to why the ECM will not allow me to increase target idle and fails to maintain the minimum idle with the ac on.
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        This gallery has 2 photos.

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        • #5
          Why is your fuel pressure indicating 142 psig and your AFR SP 0. Seems to me that would cause all sorts of problems.

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          • #6
            Thanks for the reply, there is no fuel PSI input to the system and I assume that is the default reading. Actual pressure is 58 LBs.
            Don't know what AFR SP is and not sure it has anything to do with what I am asking ? As stated the car runs fine.

            I found AFR SP (air fuel ratio set point) in the manual. I surmise that reading is in error. And agree that if the ECU was really trying to maintain zero the car would not perform well
            Last edited by johnatkens; 08-21-2020, 06:49 AM.

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            • #7
              That kind of puzzling that the AFR SP is reading zero. After you tap Edelbrock on you tablet go to Advanced Tuning > Air Fuel Ratios and you should see 3 Set Points, Idle, Cruise, and Acell. What are they? Now go back and tap Diagnostic Mode. Any red buttons?

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              • #8
                Customer " JohnAtkens" Does not have a Pro Flo 4 kit.

                He has GM Performance EFI crate engine with a NON-Tunable Calibration. https://www.chevrolet.com/performanc...zz6-efi-deluxe


                So it looks different than a PF4 display ==no Fuel pressure sensor, AFR SP = is not settable.

                With his tune he is unable to adjust anything.

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                • #9
                  Originally posted by 2700 Cast View Post
                  Customer " JohnAtkens" Does not have a Pro Flo 4 kit.

                  He has GM Performance EFI crate engine with a NON-Tunable Calibration. https://www.chevrolet.com/performanc...zz6-efi-deluxe


                  So it looks different than a PF4 display ==no Fuel pressure sensor, AFR SP = is not settable.

                  With his tune he is unable to adjust anything.
                  THANK YOU, that is the answer I needed !
                  FWIW the owner likes this system so much he is planning 2 more installs this winter, both will Pro Flo 4 kits

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                  • #10
                    Wow, roll me over and pat me down with flour. My dumb azz didn't see that this is a non ProFlo 4 system or a third party poster.
                    Last edited by CorkyE; 08-22-2020, 07:39 AM.

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