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Thread: SBC 350 Idling Problems

  1. #1

    Default SBC 350 Idling Problems

    Hi. I have a SBC 350 mated to a Turbo 400. Have recently installed a new cam, very mild and valve springs other than that stock. Having a lot of issues with the Atomic unit idling. It's always surging the air fuel ratio goes between 88-130. Once you have it above idle it seems to work a lot better.
    ECT 78°F
    IAT 27°F
    TPS 0%
    MAP 62 kPa
    Fuel 250 psi
    A/F Ratio 1.26 Lambda
    Inj Duty 5%
    Ignition Timing OFF
    IAC Position 46%
    Any help would be appreciated.

  2. #2

    Default

    From your live data, the calculated manifold vacuum is only 11 inHg if at sea level, should be higher with a mild cam. Verify the cam timing is OK and check for vacuum leaks. The fuel pressure should be around 42-45 psi. Make sure there are no exhaust leaks near the WBO2 sensor giving a false lean AFR. And the IAC count is too high, you'll need to open up the throttle blades. What's the ignition timing and AFR targets?

  3. #3
    Join Date
    Jan 2010
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    Default

    A Lambda of 1.26 is way too lean for idle. Your engine is struggling to run at that lean ratio. Hence the IAC count, and the low manifold vacuum. If you have done an engine rebuild and fit aftermarket EFI at the same time, then too many variables to pinpoint your trouble.
    If you can be sure the engine is mechanically sound, (cam timing correct, valve lash, etc), then you need some more fuel, and possibly ignition timing. What parts are you using in your ignition system, and is the timing controlled by the Atomic? Gary
    Regards, Gary

  4. #4
    Join Date
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    Default

    And what's up with 250 psi fuel pressure?
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, 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, -6AN fuel system plumbing, Walbro 255 LPH pump, 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 M/T Street Comp tires.

  5. #5
    Join Date
    Jan 2010
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    Default

    Yes, I didn't see that Danny, well spotted.
    250 psi or 250 kPa?
    And then coolant is 78°F, which is cold, and IAT is 27°F, which is below freezing.
    So there is so much wrong is this data list, I can't see how the engine is lucky enough to start.
    Can the OP please check your data list, and post a photo from your display? Gary
    Regards, Gary

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