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Thread: Truck running poorly.

  1. #1

    Default Truck running poorly.

    So I recently installed the Sniper EFI & HyperSpark distributor and Holley CD box on my fresh 383 in my Suburban. It runs & drives but it's missing semi-inconsistently and I feel like it's low on power, but who knows. It's a new engine so I have nothing to compare it to. It's really obvious for some reason when I shift to 3rd and accelerate at medium to heavy throttle. Sometimes it sounds slightly off at idle too. It's got a dual-plane intake with the center partially milled out. I have the progressive throttle linkage installed and that setting which I can't remember off the top of my head is put into the computer.

    Things I've checked:
    Pulled all plugs which were new with the new engine and 3 of the 8 did look richer than the others, but weren't fouled.
    Did a compression check and all cylinders were at ~180 psi.
    Checked at night for any arching, but saw none. Wires are almost new MSD Street Fires and cap & rotor are new with the HyperSpark.
    Static Timing was checked with timing light and matched settings on the Sniper at 17°.
    Also, I just double checked the timing by setting the timing to 20° on the handheld and checking with the timing light from idle till about 4000 and it held stead the whole time.
    I just did my first real datalog, but for some reason it's telling me it's not a valid file, but I can see it on my laptop using the Holley EFI software. Thank you for any help as I really need this rig running right. EDIT: I think the datalog should've worked now.
    Attached Files Attached Files
    Last edited by Gandyman64; 10-08-2019 at 07:04 PM.

  2. #2


    Take the progressive linkage off until you have the Sniper working properly. The Sniper isn't designed for progressive linkage and you shouldn't be re-engineering your Sniper until you have some expertise.

  3. #3


    I'll try that tomorrow. Before I put it on it drove absolutely terrible as it's a manual and the getting going was just miserable with the stiff pedal and spinning tires every time you give it the smallest amount of throttle.

    I was messing with it more tonight and it seems I think my factory timing curve is part of the problem. In the areas it starts breaking up it was still at the static timing of 18°. Seemed if I put my foot in it further the timing would jump up to 32° or so then run great. Cruising around under 2000, it would just stay at 18°.

  4. #4


    There’s an article on EFISystemPro about timing curves. Download the Holley V5 software and cut/paste the timing table from the built in base configs into your Config File after switching timing from basic to larger 2D Table.
    If you have higher efficiency heads, let me know. I have a decent table with slightly lower advance.
    Last edited by HeavyChevy; 10-08-2019 at 10:58 PM.

  5. #5


    Thank you. I'll look into that tomorrow. I have the Summit aluminum 170cc heads that I guess are made by Trick Flow and have been blended/polished so they might not be AFRs, but should be pretty efficient. Quench is right at .40 and calculated 9.4 compression ratio.

  6. #6
    Join Date
    Dec 2009


    (Gandyman64, please don't type your posts like you're texting. It takes me a long time to edit it. At least use Spell Check before posting.)
    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.

  7. #7


    Sorry about that. Bad habit, I know.

  8. #8


    You have some wiring issues. Right click in the datalog view and select Mark Data Points. You'll see the frequency of points is not consistent and often when things get jumpy you have big gaps. How is the truck grounded? Not the Sniper, but your main battery grounds. I wonder if you have an exhaust leak too. Your AFR is all over the place.
    69 Camaro
    400 SBC, ProCharger D1SC

  9. #9


    The main battery ground goes to engine block then large ground strap to frame. There's a smaller wire from battery ground to body along with numerous straps between frame & body. I've cleaned them all and checked with a Ohm meter and it's showing I have good connections.

    I changed location of the WBO2 sensor as I have Tri-Y headers and it was only reading two cylinders and moved it down just past the collector. I checked for leaks using a stethoscope and found none.

    Here's the latest datalog since moving the WBO2 and giving it more base timing. To me it looks better, but I'm still trying to figure out what I'm really looking at. It drove way better, but seems to go too rich at times.
    Attached Files Attached Files

  10. #10


    Looks better, but I still think you have some EMI. For example, look at the 233-235 second mark. See how the AFR line goes fuzzy? That looks like interference. Are there any plug wires near your WBO2 wire?
    69 Camaro
    400 SBC, ProCharger D1SC

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