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Missing badly under load, need help!

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  • Missing badly under load, need help!

    I have the Holley Sniper 4150. Just got the truck running and I can't figure this out. The truck idles good and I've set the IAC to the adjustment from Holley. For some reason the truck will barely pull its self after about 1800 to 2000 RPM. I've checked the fuel pressure and it's staying at 60 PSI even when revving the engine, which is another thing. When in park revving the engine, there's no miss. It's fine, but under a load, it misses like crazy. I'm new at all of this so looking at the datalog is kind of hard. Seems fine other than the AFR jumping up & down. This Sniper is off of another truck and when I put it in my truck I went through the Wizard and everything. Not sure if it's RFI or what. This is also on a Ford 302 and I've also installed 9mm Ford Racing wires to eliminate RFI. Not sure what it is, but please help. I'll upload a couple of datalogs.

    This engine is a rebuild 302 from S&J Engines. It has less than 2000 miles on it. The transmission is a 4R70W Transmission with a TransGo AODE-3 Manual shift conversion/reprogramming kit and a new stock torque converter. GM HEI Distributor running in coil negative per instructions. E303 Ford Racing camshaft. No other modifications are made to this truck.
    Attached Files
    Last edited by aawill1996; 01-22-2023, 05:52 PM.

  • #2
    Are you able to confirm pressure when you have it in gear and rev it? Revving it in Park/Neutral often will not show a drop in pressure, but a clogged filter or poor performing pump may not be able to keep up when there's a true load on it. Incorrect timing, poor spark, or excessive plug gap can also cause this type of problem, so look beyond fuel.

    We need to see your Config File in order to properly evaluate the datalogs. Download the Config File from the ECU using the Save As function. Rename the file so we can be sure we are looking at the Config File stored in Sniper memory.

    While checking things remove the air cleaner and have someone turn on the ignition while you're looking down the barrels. Ensure that all four injectors are providing a prime shot. A failed injector or loose injector connector may allow the engine to idle, but not to operate under load.


    • #3
      aawill1996: Missing because of a fuel delivery problem, or an ignition system problem?

      Originally Posted by Danny Cabral
      Clamping a timing light on each cylinder, works well for misfire detection (watch for consistent flashing).
      Test drive it with a timing light taped to the windshield if you have to.

      Also, ensure all the fuel injectors are operating. You can use an injector noid light (LINK), an injector probe (LINK), or even
      a long screwdriver used as a stethoscope (placed between an injector and your ear, listening to each working injector).
      Other less definitive methods for MPFI applications, include infrared temp gun readings on header primary pipes,
      or a wet rag on header primary pipes. However you do it doesn't matter, just confirm combustion on all cylinders.
      May God's grace bless you in the Lord Jesus Christ.
      '92 Ford Mustang GT: 385"/6.3L SBF, Dart SHP 8.2 block, forged steel crankshaft & H-beam rods, forged pistons, Trick Flow Twisted Wedge 11R 205 CNC Comp Ported heads, 12:1 compression ratio, 232°-244° duration/.623" lift/114° LSA camshaft, TFS R-Series FTI Comp Ported intake, BBK 80mm throttle body, Holley Dominator MPFI & DIS, Holley 36-1 crank trigger, MSD 1x cam sync, PA PMGR starter, PA 200A 3G alternator, Optima 34/78 Red battery, 100HP progressive dry direct-port NOS, R134a A/C, Spal Dual 12" HP 3168 CFM fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, Earl's -6AN fuel system plumbing, Walbro 255 LPH in-tank pump & Pro-M -6AN hanger, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio Ford AOD, 10" 3000 RPM C6 billet converter, B&M Hammer shifter, Stifflers transmission 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.


      • #4
        I've been helping aawill1996 with the project. So I'm available to try and answer any questions that'll help him get this thing running appropriately. Thanks for the help. All advice is appreciated.


        • #5
          We need the actual Config File so we can see what the Learn data looks like. Are you tying into the Sniper TPS signal for the transmission, or do the modifications not require a TPS signal?


          • #6
            OK, I have figured it out. The bug I believe going to drive it some more tomorrow. I checked fuel under load only drops 1 psi, but when checking timing under load it was erratic. I found that it was dropping voltage to the distributor, how why, don't know but I found another 12V wire on original truck harness and now runs great. Thank you for everyone's help I greatly appreciate it and will let you know tomorrow if all is good. And if not I'll pull the Config File and post it along with another datalog. Thank you.

            And the Holley is tied into a hot wire by itself, it's actually the wire that goes to the old injector harness. The transmission is full manual with that kit, so there's no TPS needed and would not tap into it even if I needed to because Holley says not to.