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Discussion Starter · #1 ·
I just finished installing my MS CAI w/ straightener and I also have a dashhawk. I am getting AFR's from 20 to 30 whenever I let off the gas when cruising while still in gear. I reset the ECU and have not gone WOT. I am not worried about my LTFT and STFT (6 to 10) since I just installed the CAI and reset the ECU. I understand the fuel trims will get better after some more mileage.

But I never paid attention to my Air/Fuel ratios before I installed my MS CAI so I am not sure if the 20 to 30 AFR after letting off the gas pedal is normal. This also happens to me when I am idling, give it the car a little gas, not WOT but just to rev it up a maybe 1000 rpm and then let off the gas. Again the AFR goes up only after I let off the gas pedal.

I am trying to think through it and the only reason I can think of is that after I let off the gas, the BOV recirculates the air which could in turn give me high AFR.

Let me know if this is completely normal or is my car a ticking time bomb.
 

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Mine jumps that high whenever I let off the throttle...but dont worry about that...its normal.
 

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It is normal because when you are engine braking you are not using any gas... Totally normal. My afr gauge only goes to 20 and it goes to that and blinks which means it is above 20. You are totally fine. You should only worry if you are cruising or stomping on the gas.
 

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Normal...mine is 29 deccelarating. Your car is not a ticking time bomb. :) Enjoy it. And I've ran worse fuel trims with the mscai, so your fine.
 

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The car measures the AFR in terms of lamba from 0 to 2 with 1 being a perfectly stoich ratio of 14.7:1. If the car is not injecting fuel, the leanest the sensor can read for lambda is 2 which translates to 14.7x2 or 29ish.
 

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Discussion Starter · #9 ·
Thanks guys, that helps relieve alot of worries. I haven't pushed my speed3 hard at all since installing the MS CAI. Will probably wait for more mileage so the fuel trims can get better. But under normal acceleration the AFR's are around 14.7 to 15. I am going drive it again tonight and log it on my dashhawk just to make sure.

Thanks again folks
 

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Sounds like things are running normally, then... never hurts to be too careful :) Just make sure that it richens up when you accelerate hard under boost (you might see as rich as 10.5:1 at WOT in some gears).
 

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I just got my DH too, and I'm seeing 29.xx on my AFR when i let off the gas or engine braking. So I'm glad I ran into this post. One thing I am concerned about ismy AFR when cruising...it is at about 14.xx...I thought a safe AFR is suppose to be 11-13? Am I at risk here??? Or are you guys just talking about AFRs at WOT (or near WOT)? Thanks.
 

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[quote author=kalix link=topic=137744.msg2984256#msg2984256 date=1236642716]
I just got my DH too, and I'm seeing 29.xx on my AFR when i let off the gas or engine braking. So I'm glad I ran into this post. One thing I am concerned about ismy AFR when cruising...it is at about 14.xx...I thought a safe AFR is suppose to be 11-13? Am I at risk here??? Or are you guys just talking about AFRs at WOT (or near WOT)? Thanks.
[/quote]

Cruising at low loads anywhere from 14-16 is safe, the car is targeting best fuel economy. It should only dip below 14.x when you're getting on it pretty good.
 
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