Low range engine braking issue

[Pilch]

Has anyone had any issues with their KK when engine braking in Low Range? When engine braking in 1st low range my KK gets to around 1800rpm and will then accelerate on its own all the way to redline. This however does not happen in 4WD Auto or 2WD.

Any thoughts on the cause before I start throwing new parts at it? My first port of call is to replace the TPS.

Any help greatly appreciated.

[Wiz.au]

I don't know for sure, but I'm wondering if you 'need' to engage the "Hill Descent" for low range engine braking to function like we all would expect?

I'll try mine next chance I get and report back.

Oh, Throttle Position Sensor...not likely I would think. If the TPS was faulty, your vehicle wouldn't drive right.

In fact I can't think of any individual sensor that would cause that. To my thinking, it's the software in the ECU that is not doing what it should based on the input it is receiving from the various sensors: Wheel speed via ABS rings, Engine RPM via Crank Angle Sensor, Throttle position from TPS, Gearbox Pressure sensors from Valve Body & Gear / 4WD selection switches.

If ABS or RPM were faulty your Dash Tacho and Speedo would be jumping around all over the place, which I HAVE seen.

Anything else should throw a fault code. Actually, that would be the best place to start if you haven't checked already. See what OBDII codes are logged, if any?

[MidnightMods]

My JKUR will run away in 1st LR, You still need to tap the brakes or shift up. the hill descent will just pulse the brakes, leading to very hot brakes and a scary ride so use with care.
I found I need to shift up to 2nd or 3rd, apply the brakes and then shift back down (auto) to keep it under control.

[spoondog]

I have a manual 3.6 Jku and it will hold for a bit but as soon as the revs creep up a little it also runs away, I have to keep tapping the brakes to keep a steady speed. And if I use any throttle at all just to try and get a little bit more speed it takes off. My old 3.8 manual was the same.
I put it down to the poor throttle mapping, the two jk's I have owned have had the worst throttle lag of any car I've owned.

Sent from my SM-T805Y using Tapatalk

[MidnightMods]

Throttle control mapping changes in low range Vs high range .
But yes the hi range mapping is pretty crap

[Pilch]

Thanks all for the responses. I'm off on another trip in acouple of days so will try a few things and definitely take a look at the OBDII for any fault codes or unusual outputs.

Would an aftermarket throttle controller like the wind booster likely have any impact?

[MidnightMods]

Not in low range because the delay is disabled.

Its not the throttle that is making the car run away, I would think its tuned that way to avoid damage to the engine and drive train to reduce pressure on the drive line.
After a few trips I worked mine out and I feel happy and safe in using engine braking even in extreme descents