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Thread: Bosch 49 sticks at 15-15.3 AFR.

  1. #11


    GPatrick, the engine I have likes a lot of initial timing. Before the Sniper, I ran an HEI setup with a boost retarder. I set initial advance with vacuum and mechanic locked for best vacuum readings, then limit mechanical to be all in by 3000 RPM for max of around 34°. From there I limit vacuum advance to not exceed 44°. The Base Timing Table for my setup, I did my best to mirror the HEI settings.

  2. #12


    Thanks for the overview of your timing. Boosted applications are way outside my range of experience. Reinforces the recommendations of knowing your existing timing before moving to timing control. Any luck on the stuck AFR issue?

  3. #13


    My Sniper is being sent back to Holley for testing & repairs. They must be very busy as everything is taking a long time. I'll let you know how everything works once I get it back.

  4. #14


    No luck sorting anything concrete out. I did find this though:
    Sensor failures related to Lambda 1.01 (roughly 15 AFR) could be caused by damaged wires. So this gives me something to look at. Other sources talk about how the sensor heating cycles are performed as some cheap WBO2 indicators put full power to the Bosch LSU4.9 sensors and this burns them up. If the Sniper had a bad algorithm for sensor heating, I'd think more issues would be noted overall regarding failed sensors. Therefore I think the issues related to my problem must be with either my installation or something malfunctioning in my EFU unit.

    UPDATE: A bad PCV/design flaw was allowing oil to be sucked in by the blower. This must have been just enough to throw off the WBO2 readings, but not enough to cause oil/carbon fouling on the spark plugs. The new spark plugs I installed all had fresh oil on the low side of the plug face, but were otherwise pretty clean. This told me something was off. I pulled the blower and found it was coated in oil. After ruling out intake gaskets and valve guide seals, the only thing left was the PCV system.

    I ended up redesigning the baffles in my air/oil separator, using a different PCV valve and installing a one way check valve on the breather side to reduce outside air under vacuum, but allow for pressure to escape at higher RPM or when the PCV system's ability to pull vacuum is exceeded. All in all $5 dollar fix plus fabrication time. If anyone else is experiencing an abnormal lean condition that hangs at 15.1 - 15.3 for no good reason, check your PCV system and for any oil in the intake.

  5. #15


    Thanks for the update. Holley said they'd send me a service ticket, but it has not shown up. I swapped my unit out with one a buddy had (his wouldn't control timing) and my car is running very well. Hopefully I'll get mine fixed soon.

  6. #16


    I've also dealt with oil contamination. Designed my own baffles to keep oil in valve cover and out of PCV. First thing to check when you see lean AFR is the plug wires. You really need to look sometimes they barely burn, but up close you can see it. The Sniper I spoke about sticking at 15.1 was sent back. I don’t know for sure, but I thing a injector got unplugged as the spray pattern was not the same in all four barrels. Symptom was car ran hot & bad. After recieving back from Holley, the Sniper worked flawlessly.

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