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Thread: 408W with Sniper EFI Project

  1. #1

    Default 408W with Sniper EFI Project

    Here we go!!! This is a post documenting my Holley Sniper EFI install. The Sniper unit replaced my Mighty Demon 750 annular carb on a 408 Clevor build 512hp/520tq. The Sniper setup is running in CD Box configuration, the current distributor is a Mallory Max-Fire which has been running great. The Sniper setup has over 250 miles on it and has been running very well except for the last two weeks around March 1st 2019. We wanted to have several hundred miles on the Sniper before we installed the Dual Sync distributor, MSD 6AL Digital+ and coil. But, we didn't make it. :-( Initial install and seat of pants was a non-eventful and a significant improvement over the Mighty Demon for various reasons.

    After having it towed home via Haggerty on 3/12/19, I started the troubleshooting process, both with Holley documentation and videos, along with forum threads and YouTube videos.

    Issue as of 3/1/19 - While driving the vehicle would suddenly increase RPM without throttle change. This was intermittent and prevented us from moving to the Dual Sync install, as we wanted to make sure the system was working correctly before introduction a new component.

    Issue as of 3/12/19 - Engine will start but will not maintain idle, AFR reads init, heat...35.6. It takes 20-20 seconds after fuel pump primes before it will move from init...heat, etc. which is new. Previously it would crank & read AFR as it should.

    I've performed all of the wiring checks, voltage checks, sensor readings, etc., via the Holley troubleshooting documentation. I have several datalogs of running normal then the problem begins intermittently to today where the problem is constant.

    Click image for larger version. 

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    Last edited by crabbdaddy; 03-13-2019 at 12:38 PM.

  2. #2


    After contacting Holley support, I sent photos of the WBO2 sensor to verify correct installation. Progress! New WBO2 sensor being shipped under warranty.

  3. #3


    If you have a dual-plane intake with no crossover, you could have a bad injector connection. I just had one with mine. Engine rough with high AFRs, would suddenly smooth out and accelerate without input. Would not idle. Repaired the connection to the front passenger injector and all is well. If you look down the throttle bores while someone turns on the key you can verify injectors are working when engine primes; easy check. Even with an intake crossover, mine was experiencing all your symptoms.

  4. #4


    Did you try running the system in Open Loop? If it runs fine in Open Loop, then yes, a bad WBO2 sensor.
    '73 K5 Blazer, built 350 SBC 375 HP/425 TQ, 12" F/18" R suspension travel. Deaver springs with King shocks, D44/12 bolt, 3.73 gears, lunchbox locker F/Auburn Posi R, crossover steering, 35" BFG Mud Terrains, Vintage Air system, PRP suspension seats, lots of custom work, all built by me.

  5. #5
    Join Date
    Dec 2009

    Default (WBO2 Sensor Test At End Of "Wideband O2 Sensor Notes")
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 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.

  6. #6


    Quote Originally Posted by Crusty Old Shellback View Post
    Did you try running the system in Open Loop? If it runs fine in Open Loop, then yes, a bad WBO2 sensor.
    Yes, Open Loop did not work due to various reasons. When the WBO2 was going out, my plugs were severely soaked in fuel. I guess the system was trying to compensate. I'm running a single-plane Track Boss intake, no injector issues. Thanks!

  7. #7

    Smile Issue resolved!

    Okay, she is running better than ever! So I finally had time to dig in and work on the '69. The issue was a bad WBO2 sensor that I replaced under warranty around two weeks ago. But why didn't it run great after replacing the WBO2...well I finally had time to troubleshoot this weekend 3/30/19. It seems when the WBO2 sensor was going out, my plugs fouled out. A great time to replace them with new set of NGKBP6ES. I'm Running AFD 2V aluminum Cleveland heads on my stroked '69 351W block. After replacing the plugs with a new set, and stepping through a new Wizard tune, the '69 is running great! Throttle response is very quick and she revs great. Well worth the trials & tribulations to move to the Holley Sniper EFI system. So much so I'm doing research on adapting traction control with the 275/35/18s, FAYS2 Watts Link & Cal-Tracs she is still a sit & spin. Good times!
    Last edited by crabbdaddy; 03-31-2019 at 10:45 AM. Reason: spel

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