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Thread: CL Comp chasing tail wildly.

  1. #1
    Join Date
    Apr 2020
    Location
    SoCal
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    1

    Default CL Comp chasing tail wildly.

    Hello everyone. I'm new here, and a novice at HP EFI. Have no posted in the forum before. My engine is a zero-time Chevy 572, and I guesstimated the Target Air/Fuel Ratio based on looking over other calibrations for big blocks. Engine has never been run on a carburetor. Cam is 250°/260° int/exh @ .050". Car is 3400 lbs, clutch, 3:73 final.

    Does anyone have calibrations for this engine they're willing to share? Not much usable on web searches.
    Due to work/family, I don't have time to do the entire tune from scratch.

    I turned off idle timing as it was fluctuating quite a lot, and CL Comp is similar.

    Advice on things I can try to stabilize the CL Comp? It should target 14.7 at 950 RPM idle at all MAP kPa, but returns between 14.0 and 17.2.
    Even with 14.7 commanded, it still idles slightly fat with a light haze gray smoke. Plugs are pretty dark, but still showing some tan and no sign of oil.

    Exhaust is tight, WBO2 is just after collector, car has never been driven, only idle time and some revs to start basing in the Accelerator Enrichment.
    Thanks for any data and advice for this engine. Eric
    Last edited by SixFour; 04-07-2020 at 08:33 PM.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    25,081

    Default

    I'd stop and get someone to help you (this might mean a remote tuning session). I'd contact Chris Myer at EFISystemPro.com or Richard Nedbal (FastManEFI) at EFIExpert.com.
    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

    I can help you. That cam will require some special tuning at low RPM. A remote session is really a training session for you, that ends with your engine being tuned. Go to my website and either send me an email or call me.
    Rich Nedbal
    fastmanefi.com

  4. #4

    Default

    Quote Originally Posted by SixFour View Post
    Hello everyone. I'm new here, and a novice at HP EFI. Have no posted in the forum before. My engine is a zero-time Chevy 572, and I guesstimated the Target Air/Fuel Ratio based on looking over other calibrations for big blocks. Engine has never been run on a carburetor. Cam is 250°/260° int/exh @ .050". Car is 3400 lbs, clutch, 3:73 final.

    Does anyone have calibrations for this engine they're willing to share? Not much usable on web searches.
    Due to work/family, I don't have time to do the entire tune from scratch.

    I turned off idle timing as it was fluctuating quite a lot, and CL Comp is similar.

    Advice on things I can try to stabilize the CL Comp? It should target 14.7 at 950 RPM idle at all MAP kPa, but returns between 14.0 and 17.2.
    Even with 14.7 commanded, it still idles slightly fat with a light haze gray smoke. Plugs are pretty dark, but still showing some tan and no sign of oil.

    Exhaust is tight, WBO2 is just after collector, car has never been driven, only idle time and some revs to start basing in the Accelerator Enrichment.
    Thanks for any data and advice for this engine. Eric
    I agree that with an engine like that and your limited experience and time you should call Rich for a professional tune. However, you might be able to get it stable before you call Rich which will save you both some time. To get the engine stable I'd suggest raising your Target Idle Speed to 1200 RPM for now. Just increase the Target Idle Speed in the software and fire up the engine. Look at the IAC Position and then adjust the idle speed screw to stabilize the IAC Position around 20%. If you can get the engine to warm up and run at 1200 RPM with the IAC at 20% then you're halfway there. Once you have it running at a stable fast idle you can drop the idle speed to 1000 RPM and see if you can get it stable at the lower speed. If you can get it stable then take note of the fuel being used and then compare that to your Base Fuel Table at the same point. You want the Base Fuel Table to have the same values as what the engine uses. That way the ECU doesn't have to do so much adjusting.

    A target of 14.7 AFR at idle most likely is not going to work with a performance engine. Change the idle target to 13.5 AFR and it might idle for you. And it isn't fat at idle with a target of 14.7 AFR. It's actually lean and misfiring due to the lean and the misfires dump raw gas out the exhaust. Your nose tells you that it's rich, but your nose doesn't understand what's happening inside the engine.

  5. #5

    Default

    Is Closed Loop actually oscillating? You may have cylinder imbalance. Very common on engines with non-EFI intake manifolds.

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