I know that rev hangs are intentionally introduced to modern vehicles that operate on electronic throttle bodies, by programming the ecu to close the throttle valve slowly (in gasoline engines) even when you let go off the accelerator pedal quickly ,so that you can reduce emissions.

I have read that when you close the throttle valve quickly it takes some time for the fuel injectors to cut off the fuel supply making the air-fuel mixture available in the engine to be richer thus causing higher hydrocarbon emissions. So my question is "Will letting go off accelerator at high engine load conditions (say you are flooring it and letting it go completely) will increase the duration of rev hang?".

My logic behind this is that fuel injector will be supplying more fuel at higher loads and hence letting go accelerator at higher load will result in more amount of fuel injected before it responds and cuts off fuel. To burn of this extra fuel completely then you would require more air and hence increased duration over which the throttle valve has to be kept open by the ecu (i.e rev hang). Also in port fuel injected vehicles there will be some fuel that wets a portion of intake runner and this fuel that wets the runners cause more rev-hang in port fuel injected vehicle.

Here is the video explaining rev hang: https://www.youtube.com/watch?v=mm6SSeLivqE

Also a counter argument to this could be that the throttle valve will be opened more at higher loads so the ecu doesn't need to maintain/keep the throttle valve open for an even larger duration to burn the excess fuel injected.

Here is video that seems to show that you have more rev hang at higher load: https://www.youtube.com/watch?v=INtfe3xJXF8

Also what are all the factors that can affect rev hang?

  • I'm not clear that this is related to "Motor Vehicle Maintenance & Repair".
    – jwh20
    Jul 1, 2021 at 17:52
  • 2
    I’m voting to close this question because it's not really about Motor Vehicle Maintenance & Repair but rather design and/or theory of fuel injection systems.
    – jwh20
    Jul 1, 2021 at 17:53
  • @jwh20 A lot of the questions in this site seems to be theory stuffs. But if you would suggest a better alternate site for asking the question it would be helpful. Thanks Jul 1, 2021 at 17:58
  • How about engineering.stackexchange.com
    – jwh20
    Jul 1, 2021 at 18:22
  • @jwh20 I thought about it too but as it turns out engineering is not limited to just automobile engineering alone. There are a lot of branches in engineering and i hope you know that. And i felt this the place that should/would be having more number of people focussed on automobile knowledge than a general site for engineering. Or the least this site has more similar questions like the one i just posted. If you still feel like this question has nothing to do with this site then I have nothing more to prove my point. Jul 1, 2021 at 19:35


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