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Thread: First Drive Out

  1. #1

    Default First Drive Out

    So, I finally got this thing to move under its own power the other day. When I was pulling out of the garage in the driveway it was idling just fine, when I blipped the throttle to move it some more, RPM went up as did AE, but then it almost went down to 300 RPM. What's strange is I see my spark moving from my Base Spark Table of 20° to 28°. So I'm assuming Idle Spark control has to do something this.

    I'm thinking definitely something with DBW and Ramp Down, idle etc. When I look at the datalog I see IAC at 30%, which is what I'm showing as my IAC Hold Position. I have Ramp Decay at 3.0. RPM above is 1000, RPM to Re-enable is 50 RPM.

    When I'm looking at the datalog, I'm seeing RPM fall, but then I see IAC jump to 44% from my 30% even though my TPS is showing 9%. Timing jumps from my base 20° to 28°, which again leads me to Idle Spark.

    As soon as IAC jumps to 40ish and even jumps to 50% is when the RPM starts dropping to almost 300 when I'm commanding 780 RPM. I think I'm in the ballpark of the correct area to look, but I'm not sure what it could be. AFR is showing a bit rich, but I wouldn't think that would be enough for it to stumble. P Term is 40 and D Term is set at 60. Thank you in advance.
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  2. #2
    Join Date
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    Default

    Quote Originally Posted by 72tutone View Post
    What's strange is I see my spark moving from my Base Spark Table of 20° to 28°. So I'm assuming Idle Spark control has to do something this.
    Yes, that's the Idle Spark control varying the ignition timing to stabilize/control the idle RPM. It can be temporarily be disabled (Idle ICF) when viewing the idle timing with a timing light.
    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.

  3. #3

    Default

    Thanks Danny. I figured as much. I'm just trying to figure out as to why it plummeted so much. In the attached datalog from 3.4 seconds into the datalog you can see it go from 2180 RPM and slowly creep down to 300 or so RPM.

    Why would RPM fall and kPa go up? That doesn't make much sense to me if throttle is closed. Shouldn't kPa be going down as I'm in vacuum as the throttle is closed?

  4. #4
    Join Date
    Dec 2009
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    Default

    Quote Originally Posted by 72tutone View Post
    Why would RPM fall and kPa go up? That doesn't make much sense to me if throttle is closed.
    Because there's not enough RPM to produce vacuum.
    Low numerical kPa is high vacuum. Higher numerical kPa is low vacuum.

    Shouldn't kPa be going down as I'm in vacuum as the throttle is closed?
    Not when the RPM has dropped well below idle.
    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

    Default

    Get your fuel dialed in first. The part most missed on any idle routine is proper fueling at idle. Without this dialed in, there are no parameters in spark or idle that will fix erratic conditions.

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