Rev hang

[Mrbuck50again]

So this engine has been in the JL for 6 years now and no one has figured out how to fix rev hang on the manual transmission ? Several months ago I was playing with JScan and clicked to delete all error codes (although it didn’t show any) and VIOLA…next time I drove it, rev hang was gone. It lasted for about a month. It’s now back and I sure do miss the short time I had without it.

anyone have a clue on how to fix this?

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[Pape]

Can you reproduce what you did the first time or it was only a coincidence ?

 

[OldGuyNewJeep]

3.45 gearing? Shifting past 4000 RPM?

4.10 or 4.56 and shifting by 3500rpm and no noticeable rev hang.

No livernois tunes available that I am aware of.

 

[Mrbuck50again]

I have to say purely coincidence at this point.

yes old guy …3:45 gears. Yes I occasionally like to shift above 4k. Yes below about 3800 I get no rev hang.

it’s just crazy that no one can figure this out. It seems to be consistent through the manual JL’s. To the best of my knowledge Livernois has not figured it out either. I think most of us are just dealing with it so therea not much demand for a fix.

 

[alphawolff]

It's a tune thing. You'd need to tune it out. Not really many available for the 3.6, especially with the gpec5 pcm

 

[Bayrat]

I agree!! Both of my JK stick 2dr did that, and it's annoying as hell.

 

[COBill]

Note that rev hang is designed into newer manual transmission vehicles as it helps with emissions:

If you've driven a modern car with a manual transmission recently, you've probably experienced rev hang: the annoying phenomena where even after you take a car out of gear to shift up, the revs stay elevated instead of dropping to idle like they should. Well, it isn't some side-effect of a low-quality throttle body or heavy flywheel—that rev hang is engineered in from the factory to reduce emissions.

As Road & Track contributor Jason Fenske explains in his latest YouTube video, rev hang in most modern cars with stick shifts is a result of manufacturers attempting to reduce emissions generated by the engine during gear changes. Why? Well, even after you let off the gas, there's still some fuel remaining in the intake manifold from the injectors that can get sucked into the engine off-throttle. That extra fuel causes a rich air-fuel ratio, which is bad for emissions.

Since modern cars have electronic throttle bodies, the car's ECU can delay how much the throttle actually closes, despite your foot being all the way off the throttle. The delay allows air to mix with the remaining fuel in the manifold, burning off any excess that might otherwise cause an undesirable, high-emission scenario. This throttle delay is what causes rev hang.

If you despise rev hang enough for it to be a deal-breaker in your next new-car purchase, we suggest going for a car with direct injection. Because direct injection shoots fuel directly into the cylinder rather than the intake manifold, there's no excess fuel sitting in the manifold between gear changes that needs to be burned off. As Fenske states, however, there's still a possibility some rev hang can exist due to other reasons. So make sure to drive before you buy.

YouTube: The Big Problem With Modern Manual Transmissions - Rev Hang

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