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Thread: 4Di Idles Too Rich

  1. #1

    Default 4Di Idles Too Rich

    Trying to get the idle AFR around 14.7, and no matter what we do, can't get any less than 11-12 in neutral. It will go to 14-15 in gear, but slowly creeps back to the 11-12 range. This is a stock 351W, so nothing crazy. Also, the oxygen compensation always stays at 0, even when driving. The AFR when driving & WOT is fine. Just the idle seems to be nonadjustable. Any help with this is greatly appreciated.

  2. #2
    Join Date
    Dec 2009


    Quote Originally Posted by 2rods View Post
    The AFR when driving & WOT is fine. Just the idle seems to be nonadjustable.
    The TPS voltage at idle (on the 4D & Di systems) has to be set at .58 volts. This is imperative for proper operation.
    If you adjust the idle speed, you must also reset the TPS sensor voltage at idle. Read page 34 below: (Holley Pro-Jection 4Di Manual)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3


    "NOTE: If using a laptop computer, go to Data Monitor. Loosen the TPS screws. Adjust the sensor until the throttle angle
    reading is 29-31. If a laptop computer is not available, use the following method for setting TPS:"
    The throttle angle is 30, so thought it's in range, but can check voltage with meter to confirm. Thanks.

    Voltage is .58. Is there anyone else that has this problem?
    Also, I don't think it's going into Closed Loop as O2 Comp is always at zero.

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