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Thread: Mid-Range Misfire Problem

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  1. #1

    Default Mid-Range Misfire Problem

    Hey guys, I'm absolutely banging my head against a wall with a Sniper issue and hoping you all can help. This is a 2BBL unit installed on a freshly rebuilt Land Cruiser 2F engine. The truck starts, idles, and runs fine at light load but as soon as I go to heavy throttle (50% TPS & up) the truck starts to misfire & breakup. If you tip out of the throttle it will clear up and start to pull again. If you suffer through it the engine clears up once it hits 3000 RPM or so. It seems less sensitive in the lower gears, but definitely exhibits the problem in 3rd and 4th. Sometimes it's worse than others but it's never completely gone.

    I've been troubleshooting this for weeks and have done the following:
    Checked, rechecked, and rechecked fuel delivery. Always a solid 58 psi.
    Checked timing repeatedly, changed out the distributor and all ignition components.
    Varied plug gap from .030" - .055" with no effect.
    Switched the throttle body unit from another truck to this one and reran the wizard, still had the problem.
    Swapped the handheld between the two trucks, reran the Wizard, still had the problem.
    Wrapped the wiring in aluminum foil as much as possible to shield from RF interference, no change
    Changed out the WBO2 sensor, no change

    I've run a lot of datalogs and spent over an hour on the phone with Holley. I sent them my config file and datalog and they were completely stumped. They pointed me back to ignition problems or something else in the main engine.

    Attached is a datalog file that has a series of pulls. I start from a roll and go to WOT in 3rd gear letting the truck do it's thing. Then I shift to 4th and repeat. After letting off in 4th I let the truck slow down then do a pull in 2nd followed by another in third. In the pulls you can see the Learn percentages are sky high and it's not correcting AFR well.

    In talking with Holley and my own looking at datalog files no one can figure out why the system is going to such high Learn percentages and running rich. During driving it seems like as I tip out and manifold vacuum comes up the system gets happy again and is able to resume good fuel control. The WBO2 signal seems noisy to me, but it's isolated from the ignition by the engine block so I doubt it's getting interference. The truck is definitely running rich when it's misfiring, I've already changed out one set of plugs and the tailpipe has a lot of soot accumulation.

    Any help you guys can offer is much appreciated. I'm about 30 seconds away from throwing this thing out the window and putting a carb back on the engine. 2300_2_WAA.zip sniper_0012.zip
    Last edited by ddl67; 10-16-2019 at 03:28 PM.

  2. #2
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,454

    Default

    Are you at a high elevation?

  3. #3

    Default

    Yes, we live at 8000'. I should've mentioned that.

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    23,096

    Default

    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.

  5. #5

    Default

    I'm not sure what you're pointing me to there. The timing is not controlled by the Sniper (HEI setup from DUI) and it set at a static of 10° with 24° of mechanical advance. I tried it at 5° static and got no change. The truck has only been here at 8000' and not changed elevations significantly, so I don't think that I'm dealing with a sudden change in MAP from baseline (other than the obvious throttle induced changes). I've put two other Snipers on vehicles that did just fine up here, however both were larger V8s. Not sure if that has any bearing on the discussion but it's worth noting I guess.

  6. #6
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,454

    Default

    Change your Target A/F Ratio table from "Simple" to "2D" and setup a proper Target A/F Ratio table.

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