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Thread: AFR Lean Spikes

  1. #11
    Join Date
    Dec 2009


    Yes, it's in the instructions.

    Sniper EFI Software Help Information/Instructions:
    ‒ On the top Toolbar, click "Help" & "Contents". This opens all Help topics.
    ‒ When navigating the Sniper EFI software, click "Help ?" or the F1 key.
    ...This automatically opens the definitions for that specific parameter. (Holley Sniper EFI Software & Holley 558-443 CAN/USB Dongle)
    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, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core 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, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, 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.

  2. #12


    Thank you Danny, that's were I got the info. I'll try it this morning, hopefully it will resolve my issues!

  3. #13


    So lowering the Advanced Control number to 1 helped a bit but, I found that what helped the most was lowering my idle Target AFR to 13 instead of 14. That way, the idle AFR fluctuates a lot less and not to those crazy lean numbers.

    Since I replaced the rotor, plugs, wires & ignition coil, I decided to start a new tune from scratch this morning in case my ECU Learned from worn/defect ignition components.

    Voila, I just did a 30 miles drive and the car runs pretty good now except for those deceleration lean spikes I'll have to tune, same as last time. I put the AFR number at 13 idle, 14 cruise and 12.5 WOT for now.

    I have a pretty big cam that was installed by the previous owner, I don't have the specs, but it idles at 8-10 inches, seems like it runs way better with 13 idle AFR than 14. It was running fine at 14 idle AFR with my previous components, go figure why.

  4. #14


    You have to manually tune a Sniper when the engine has a big cam. Hook up your laptop, put the Sniper into Open Loop and manually adjust the Base Fuel Table until you find the best AFR. You also need to give the engine a lot of timing at idle when it has a big cam. The Sniper can't "Learn" any of this, it has to be done manually.

  5. #15
    Join Date
    Feb 2020
    Wheeling, WV


    Quote Originally Posted by drzmat View Post
    It was running fine at 14 idle AFR with my previous components, go figure why.
    That's the question I'd be trying to answer. Sure seems to lead back to a cap, rotor, plugs & wires issue.

  6. #16


    My guess is that my initial Sniper install/ECU Learning process was with worn ignition components. When I've put the new cap, rotor, wires, plugs & coil, the Base Fuel Table I had was completely wrong and wasn't working at all.

    With a new tune done from scratch with the Wizard, it was a bit better, but still ran like crap until I changed the Target AFR. Then it was running way better, but I had some "miss" under certain conditions.

    This morning I adjusted my AE vs TPS & AE vs MAP values like I did on my initial tune and it's way better again. I also set my AE vs TPS & AE vs MAP Blanking values to 7 instead of 15. Now I'm happy to see that I'm getting there slowly!

    I still have some lean conditions under deceleration, but I'll adjust the Base Fuel Table manually. I also have some very rich conditions sometimes when I jump back on the throttle after a lean deceleration, it create a kind of bog or miss for a moment. Anyway, I'll post some datalogs as soon as I have some time. Thanks everyone for your help!

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