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Thread: Air/Fuel Ratio very erratic, please help.

  1. #1

    Default Air/Fuel Ratio very erratic, please help.

    Hi. We've just installed a Sniper and are getting very erratic AFR readings. In Learn mode it's up around 30-35 and trying to make the mixture richer to the point of blubbering. If we restart the setup and take it out of Learn mode, so it's using the base mapping it runs around 18 and sounds much better, although a bit lean. Much as one would expect at 18. I would think that the display would show accurate and consistent air/fuel mixture readings regardless of whether it's in Learn mode or not. Seems like something computer related, as we have checked and rechecked everything we can think of. Any help is greatly appreciated. Scott

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    Without datalogs and a copy of the Config File it's hard to say.
    Check for air leaks in the exhaust upstream of the WBO2 sensor. For some reason it is reading more air then it should.
    Could be caused because the spark plugs have failed from excessive fuel causing a miss fire. Check over all exhaust gaskets and welds.
    Could also be caused by EMI/RFI/Noise/etc.
    Capture a datalog. If you don't have the USB dongle, you can still perform the same by placing the 3.5" TSLCD SD card into your PC.
    Open the Holley Sniper software with your current config then overlay the datalog.
    Right click on the Graph and select "Mark Data Points". Zoom in and the marked data points should be consistently spaced along the time axis.
    Look for negative times (it should start at zero then increase in time only) and sensors that present incorrect values/spikes/etc.
    Additionally perform a few forum searches for EMI/RFI/Noise.
    Many posts and links on how to investigate further and resolve.
    1970 XW Fairmont (presented as a GT Falcon Replica), 351 Cleveland with Aussie 302 2V closed chamber heads. Edelbrock F351 2V dual plane intake manifold. Camtech CT21544 (234/238@050", 570/579lift, 2600-6200rpm quoted range, 110lobes) 1.73:1 roller rockers. AOD Transmission. Ford 9" 3.5 Diff ratio. Pacemaker #PH4050 2v Tri-Y extractors to 2.5" Hi Flow V-Tex merge pipe with dual 2.5" exhaust through Hooker Aero Chamber Mufflers. Holley Sniper EFI 4150 Super Sniper 650 with HyperSpark Ignition.

  3. #3

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    Wouldn't you think readings should be consistent without looking at datalogs?

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    The readings you see on the screen are instantaneous values for that brief moment in time.
    All analysis should be done by reviewing datalogs as it will help reveal what is happening over time and potentially reveal other issues.
    The AFR does jump around a little especially during early Learning & tuning of the tables. But should not be pinned lean between 30-35.

    Examples: With Closed Loop enabled, a small air leak in the exhaust could present a lean AFR. The ECU compensates by adding more fuel. More fuel may foul the spark plugs causing them to miss. If they miss, you get a lean condition each miss causing the ECU to compensate by adding more fuel. Now repeat as it continues to get worse. Or with the heat of the exhaust gases, one of the gaskets or welds could be expanding and contracting letting air into the exhaust system presenting a lean condition. Then the ECU compensates by adding more fuel, etc.
    Check the spark plugs. Are they fouled (black carbon/wet fuel)?
    Check exhaust gaskets, welds, look for pin holes leaks, etc.
    Perform a datalog and review. Check for EMI/RFI/Noise/negative times, in the datalog.
    1970 XW Fairmont (presented as a GT Falcon Replica), 351 Cleveland with Aussie 302 2V closed chamber heads. Edelbrock F351 2V dual plane intake manifold. Camtech CT21544 (234/238@050", 570/579lift, 2600-6200rpm quoted range, 110lobes) 1.73:1 roller rockers. AOD Transmission. Ford 9" 3.5 Diff ratio. Pacemaker #PH4050 2v Tri-Y extractors to 2.5" Hi Flow V-Tex merge pipe with dual 2.5" exhaust through Hooker Aero Chamber Mufflers. Holley Sniper EFI 4150 Super Sniper 650 with HyperSpark Ignition.

  5. #5

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    Erratic readings like that usually indicate an ignition problem. When the ignition misfires you get unburnt air in the exhaust system which the WBO2 sensor reads as lean. Pull your plugs, check your wires, do the drill on the ignition system. I'd bet that is where your problem started.

  6. #6

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    I'll check and move any wiring around the high tension leads and I'll pull the plugs and make sure none are partially fouled. I'll check header temps to make sure all are fairly even. I'll figure out the datalogging if I don't see any improvement and get back with you guys. Thanks for the tips.

  7. #7

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    Another thing could be a bad WBO2 sensor.

  8. #8

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    Good call Schweigert. I would've lost money on that one. Final update. Finally got frustrated enough with all the inconsistencies to call Holley's tech line. Jason asked for some datalogs so I got him one. He was seeing what looked like potentially a battery voltage problem, but when I ran another datalog while looking at battery voltage the voltage problems didn't show up. Jason at Holley was really patient and helpful as I was pretty frustrated. I'm sure he spent a fair amount of time going over the datalogs. He wanted to try an WBO2 sensor and got me an WBO2 sensor overnighted, but was ready to have me overnight the throttle body if it didn't help. RAN GREAT. Just like it should. So thanks to you guys and a huge shout out to Jason at Holley for his help and Holleys support system.

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