Engine surge/acceleration when downshifting

Regulator Johnson

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I just got a BL SAS, 2.7 auto. Did my first trail ride and experienced the following. When going down steep hill and manually downshifting to first or second gear, the engine would surge and the vehicle would accelerate (foot definitely off the gas pedal). Not a nice feeling when it is steep and rocky. I was in 4L rock crawl mode. Anybody else experience this or have an explanation?


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TABadlands

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Yep, unfortunately it's a thing. It was discussed at the Nevada Off-Roadeo when I attended in November. Not sure if there's a fix yet? But I know what you mean. It's a little sketchy shifting going downhill
 

mike8675309

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Yep, unfortunately it's a thing. It was discussed at the Nevada Off-Roadeo when I attended in November. Not sure if there's a fix yet? But I know what you mean. It's a little sketchy shifting going downhill
Did you mean downshifting going downhill? That's what the was stated here, it was when downshifting.

Sounds like a programming issue related to some preprogrammed shift behavior with the throttle closed.
 

Drex

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engine breaking force was overcome by gravitational force because you were going downhill. Without using the brakes, your engine revs higher due to the mechanical linkage to the tires/ground as your speed increased until your engine braking matched your downward velocity component. It is very likely that the computer opened the throttle for emissions as a rapidly closed throttle leads to increased NOx emissions. This would greatly lessen the amount of engine braking available.
 

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TABadlands

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It happened to me upshifting from manual 4WD Low toward the bottom of a hill. I didn't experience it downshifting. But I didn't downshift part way down a steep hill. I was already in manual 4WD Low at the top of a steep decline.
 
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Regulator Johnson

Regulator Johnson

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Yep, unfortunately it's a thing. It was discussed at the Nevada Off-Roadeo when I attended in November. Not sure if there's a fix yet? But I know what you mean. It's a little sketchy shifting going downhill
Was there any mention of what might be causing it, e.g., computer software issue?
 

TABadlands

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Was there any mention of what might be causing it, e.g., computer software issue?
It's definitely computer related. I don't recall the specific details the Off-Roadeo Instructor told us regarding why this happens.
 

 
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