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Thread: Rich mixture at idle.

  1. #1

    Default Rich mixture at idle.

    I installed my second Atomic, but the setup is not working properly.
    I can't get the idle mixture fixed and the set idle AFR will not be reached.
    Car is idling rich, about 11.0-12.5 AFR and not reaching its idle (650), but hanging around 750 - 800.
    Above idle, after cleaning up the overload of fuel, the mixture reaches the AFR value for cruise (14.1), without trouble.
    So it's only at idle. Yes, complete setup has been done. Including the idle adjustment.
    The first four pictures are showing the dash when the ignition has come on. The other six pictures are showing the information when the car is "idling".
    Anyone with an idea?
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    Last edited by jpf12; 01-05-2020 at 06:12 AM. Reason: Attached files

  2. #2


    Depending on your altitude, the MAP sensor should read 29.9 inHg at sea level KOEO. The calculated MAP sensor reading at idle shows only 7 inches of manifold vacuum, and the fact the idle target can't be reached, verify there are no vacuum leaks. The target idle AFR is a tad lean, try 13.8-14.2 AFR. EFI likes more initial timing as well, something like 16°-18° BTDC. I'd lower the fuel pressure as well to 42 psi.
    Last edited by tcm308; 01-06-2020 at 04:11 AM.

  3. #3


    What should the MAP reading be at idle with a stock cam? Only 7, if I understood you well? In that case, it must be a huge leak somewhere.

    Ignition timing is useless for the rich idle AFR value, as well as changing the AFR value in the handheld for now.

    Changed all the items of the Atomic today with a new one, piece by piece. No effect. Might be the always bad Edelbrock Performer intake connection to the carburetor gasket. Still not Holley shaped, but Rochester instead.

  4. #4
    Join Date
    Dec 2009


    Quote Originally Posted by jpf12 View Post
    What should the MAP reading be at idle with a stock cam? Only 7, if I understood you well? In that case, it must be a huge leak somewhere.
    7 kPa would be more like deceleration. A stock engine should idle around 20-35 kPa. (MAP kPa to inHg (vacuum gauge) to PSIG)
    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, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, BBK 80mm TB, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 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/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 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 MT tires.

  5. #5
    Join Date
    Jan 2010
    Brisbane, Australia


    Shouldn't the engine be warmed up, so it CAN Learn? Your photos show ECT & IAT just after cold start. And Learning is off.
    A stock cam should have a MAP of about 10 inches, 20 inHg on a vacuum gauge. So your MAP of 22 shows you DO have a vacuum leak that the throttle body "sees". Gary
    Regards, Gary

  6. #6


    To work out the engine vacuum using scan data, the MAP reading at idle is subtracted from the MAP KOEO value, which represents the BARO in your area. You could connect a vacuum gauge as well to confirm the readings match.

  7. #7
    Join Date
    Jan 2010
    Brisbane, Australia


    Yes, correct. So with the OP, he has MAP of 22 kPa or about 7-8 inHg vacuum. He says stock camshaft, so the Sniper is not reading the vacuum correctly, 8 would be a bracket racer cam. Most likely a leak at the throttle body gasket. Gary
    Regards, Gary

  8. #8


    JPF12, what do you have set for "Fuel Pump Type" in the initial settings?
    I agree with TCM308, the fuel pressure may be a bit high, especially for idling with a stock engine.
    The calculated manifold vacuum is a bit low too, the Atomic needs a minimum of 10 inHg vacuum.
    MSD Tech Support

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