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Thread: Suddenly I'm going 20 AFR on decel, what gives?

  1. #1

    Default Suddenly I'm going 20 AFR on decel, what gives?

    Hi. I have a Sniper Stealth 4150. I noticed driving the other day I started to go lean 20.0 AFR on deceleration and that's never happened before. So I checked for exhaust leaks and find one at header flange very small. I replaced header gasket no more leaks, but I still go lean 20.0 AFR on deceleration. I've tried old tunes that I know didn't do that still does it. I start over from Wizard with fresh tune still does it. What gives, WBO2 sensor bad? I posted a datalog of driving if anyone can look and tell me why they think I'm lean on deceleration and it can't be a tuning issue cause never did it before just started.
    Sniper_0018.zip

  2. #2

    Default

    Your Base Fuel Table is probably a little lean in that area. It most likely doesn't matter as long as the engine doesn't shut off. There's no load on the engine so running lean isn't going to hurt anything. If you want to add 10% fuel in that area of the map, you could.

  3. #3
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    Quote Originally Posted by proaudio View Post
    the other day I started to go lean 20.0 AFR on deceleration and that's never happened before. I've tried old tunes that I know didn't do that still does it.
    If your sure it has never performed like that in the past then something has changed. My first thought is the timing. When was the last time you have checked your physical timing? Vacuum leak? Look very close at the entire exhaust system from the cylinder head to a couple feet past the WBO2 for any sign of a leak.

    I start over from Wizard with fresh tune still does it.
    I don't recommend doing this. Are you able to tune it with your laptop?

    Has anything else changed, such as vacuum at idle? The problem could be anything that would allow air in during max vacuum events, meaning above idle RPM with the throttle plate closed. I don't think it's an WBO2 sensor issue. Usually when they fail they are erratic everywhere not just on deceleration.

  4. #4
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    http://forums.holley.com/showthread....1842#post61842 (Learn Table - Diagnostic/Troubleshooting Tool)
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