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Thread: Hot Start Issues

  1. #1

    Default Hot Start Issues

    Hello all. I'm hoping to get some help. I know this type of post has been put up before, I did use the search function and I'm pretty sure I have read all of the existing applicable posts with issues like this, but my problems persist.

    5.3L turbo LS engine, been running Holley HP for years on this setup and decided to change to a larger TB 90mm, and an LS2 intake. Install easy, no problems. However, no matter what settings I adjust, I cannot get this thing to consistently start cold, start hot, or idle appropriately following any existing instructions, and the IAC values are all over the place. I'm certain there are no vacuum leaks.

    The biggest thing that is very aggravating is when I did get the 5-8% IAC Position in hot idle, it just counts down to 0% IAC Position. I'm not sure why it does that, but it's perplexing. I don't understand what's commanding it to do that.

    Quite honestly the best it has run is with the dang IAC unplugged. But I know it serves a purpose so I'd like to get it right, but I have no idea if I'm getting any closer or not. I couldn't even say if it has too much or not enough fuel at cranking, but I'm assuming it is rich if I have to feather the throttle, but when I lean it out, it still doesn't start and stay running on its own.

    Here's what I have so far. I have changed all of these settings high and low, doesn't really fix what ails the car. Still doesn't want to start without hitting the throttle. It idles rough, and I have followed all directions on getting 5% IAC Position at hot idle. I've reset the TPS as required after every adjustment. The throttle has a 1/8 hole drilled in the blade. I have spent 4-5 hours messing around with this and I'm blown away that I'm no further along than I was when I first cranked it over with this new manifold.

    Idle Speed, 900 RPM
    Idle Spark P Term 30, D Term 50
    Advanced Idle Control, Slow, Stepper
    IAC Hold Position, 15%
    IAC Parked, 50% across the board
    Ramp Decay Time, 2.0 sec
    RPM Above Idle To Start Ramp, 1200 RPM
    RPM Above Idle To Re-enable Idle Control, 150 RPM
    Startup IAC Hold Time, 4 seconds/Decay Time, 4 seconds
    Target AFR 13.5
    Cranking Fuel 6 lb/hr
    Running E85, 10°-12° timing in idle area.

    I didn't change the initial settings from my setup before, but I ended up getting away from those settings since I couldn't get it to run right. With my previous intake setup I could bump the key for 2 seconds and the thing started every time regardless of air temp, or whatever.

    Any help would be appreciated. I feel like I have it all covered, but I must be missing something. Took the car to the track yesterday and was very excited to run and the dang thing wouldn't start once I was in the lanes, just cranked and cranked, got it closer tonight but still wasted a trip and lots of $$ to get there.

    I'd like to add, this car is track only, virtually no street driving. Does it really affect anything if I just unplug the IAC and set idle where it's happy at 1K RPM, and be done with it? Shouldn't really matter, right? Cam is 223°/227°, 114°+3.

  2. #2
    Join Date
    Dec 2009


    Quote Originally Posted by 80malibuturbo View Post
    Cranking Fuel 6 lb/hr. Running E85, 10°-12° timing in idle area.
    E85 fuel probably needs more Cranking Fuel.
    If you take the time to study this, you'll be a startup tuning expert: (Good Starting Advice Thread - Especially posts #2, #4 & #6.) Pay special attention to the "TIP" in post #6 of that same thread.

    I'd like to add, this car is track only, virtually no street driving. Does it really affect anything if I just unplug the IAC and set idle where it's happy at 1K RPM, and be done with it? Shouldn't really matter, right?
    Sure, if you don't need the IAC valve. However, you can't just unplug the IAC motor, because it'll be permanently open at whatever position it was when you unplugged it. It should be removed or blocked off.
    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.

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