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I agree I am nit picking now but a closed throttle and high rpm (plus
750-1500 rpm I think you said) is not quite the same as torque reversal although it is certainly indicative.This, for me, has been a very intertesting exchange and I thank you for you explanations and patience.
The point is that the ecu doesn't *need* to detect "torque reversal" to know when to shut off fuel. All it needs is RPM and throttle position.
a
Not at all. think about it - take the engine out of the car and put a handle on the crank - you can turn it with your own hand! Why is it hard to believe that thousands of lbs. of moving car can't do that? The friction of moving turning the engine without fuel is what slows you down when gearing down. It's often good practise to be in a lower gear and off the throttle when descending a steep hill - the engine resistance will slow you or keep you at a constant speed. If there were fuel being fed to the engine to "keep it running" then there would be no braking effect.
NB: I know this is the case with a manual transmission, but IIRC, there are instances where an automatic still feeds a tiny amount of fuel during "rundown".
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