Quote:
Originally Posted by theunchosen
......The ECU is going to inject roughly a gram of fuel for 15 grams of air. . .and if the throttle is closed it just means you get the same power as you would at idle(it wouldn't rev high) but you inject a ton of fuel most of which gets burned in the cat. If the air isn't getting in somewhere somehow it won't stay revved up like that, you can't burn more fuel than air allows.....
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You can't assume a constant air/fuel ratio level. Get any car on a dyno and watch the afr and you'll see it jumps around everywhere. If you put this truck on a dyno and held a constant speed and then jumped out of the throttle, I garuntee you the ratio would not sit still.
We know that when a motor runs closed loop it determines the amount of fuel to add on the fly based on input from other sensors. Its making constant adjustments all the time, it works well but its definitely not good enough to always have the exact same afr in all situations.
The way that the afr changes in this instance when you back out of the throttle is a result of how GM constructed the fuel mapping on the ecu.