Thread: Idle-Jack Dangerous in low range reverse Puma

Yeah I reckon the low reverse on a TDCi is plenty low. In the situation you describe. On the hill and stopped, low range and reverse selected, I just let the clutch and brake go and it starts off super slow and when the idle Jack feature raises the idle speed a second or three later you speed up a little - but still plenty slow. It's like engine idle was 800rpm and ups to 1000 (ish?)

On the worst slopes where you key off or stall stop. Select reverse, key it started, and again you reverse nice and slow.

I don't doubt your experiences. I know what my experiences are. Just cannot figure why there is any difference.

The only dangerous part of the idle Jack feature is when a driver doesn't know about it .... Is in low 1st/rev, trying to move millimetre by millimetre super carefully. When the clutch pedal is below a certain point the activity goes to plan, but a second or two after the clutch reaches a point up its travel and the idle speed gets a 200-300rpm boost, if sure does FEEL like a sudden uncontrolled surge - scares the proverbial out of a man.

But it's not an uncontrolled surge. It's a gentle raising of idle engine speed by 200-300rpm.

In normal operation, low 1st or low rev, the vehicle speed is fine on steep stuff, up or down.

I use low range to reverse trailers, yes it's cheating. I know it's going to lift the revs and drive accordingly. I guess going downhill ti could be a bit of a pain though.

I don't remember mine doing it going downhill though; for REALLY steep hills - I'm talking stuff on the passenger seat falls on floor steep. Maybe I was too busy clenching...

It hasn't bothered me yet but I've been driving clutch versus break at idle for decades.

It is something I've got used to now.
I also use low range for backing most trailers, it actually allows you concentrate in the mirrors with out fear of stalling.
Off road it will idle over rocks, ruts, and fallen branches with the anti stall trying to maintain 1'000rpm.
On downhill decents I find 1st is quite low and the anti stall is helpful as I drop in and out of ruts to chose the best line.

I agree it's fine going forward, so far. But Interesting that you don't mind that lurching out of the blocks experience in reverse Tact. ...I think it's something that needs to be addressed / disabled when in reverse gear. The 2.2 should have enough compression to keep running in low reverse without the idle-jack function. My TDI has no problem with doing so. ...I had a frightening experience in my Puma, with low range reverse on a steep slippery driveway! Rather than a slow controlled uptake in low reverse, with the engine braking keeping the descent safe and steady, it lurches back when idle-jack kicks in and accelerates! ...Anyone else had this experience?

Originally Posted by MrLandy

I agree it's fine going forward, so far. But Interesting that you don't mind that lurching out of the blocks experience in reverse Tact. ...I think it's something that needs to be addressed / disabled when in reverse gear. The 2.2 should have enough compression to keep running in low reverse without the idle-jack function.

Just to be clear. My TDCi doesn't "launch out of the blocks" in reverse. Reverse or 1st in low range behave the same: There is a raising of idle from around 800rpm to around 1000rpm a second or two after the clutch pedal is fully up.

Jacking the idle speed up a few hundred rpm has nothing to do with compression or lack thereof. It is about ensuring the vehicle speed is not too slow for good control on very slippery descents. Thats a LR decision. Not a bad decision I think.

There are times when maybe it would be nice to be able to over ride the feature. Like when trying to maneuver in millimetre precision through tight spots. But knowing how and when idle Jack kicks in mitigates this need somewhat.


Edit: MrLandy - quick check. When the vehicle seemed to have not enough compression and "lurched off" ... Did you have the centre diff locked? Steep slippery descents (low first or low reverse) will see you careening downhill if just one wheel loses traction while CDL is unlocked.

My driving style on steep slippery downhills is to generally "trust the vehicle" by keeping feet off pedals and just steer. CDL locked of course.

If I touch a pedal at all it will be the accelerator, counter intuitive as that may be, to bring things back under control if any slippage occurs.

I have done long greasy slippery clay downhills where there is wheel slip all the way down. But keep the wheels turning all the way, driving the throttle, blipping throttle now and then to get some semblance of steerage. A bit like driving a jet boat - no rudder - you have to hit the throttle with wheel turned to get any change in direction.

On steep rock/shale downhills - again no feet on pedals. Trust the vehicle and steer. So long as the nose is steered/pointed downhill (steering into tipping moments) the savior in sphincter moments is always "Our Blessed Lady of Acceleration".

again - all the above goes out the window if you are needing to creep/crawl through tight spots with millimeters between your vehicle and panel damage - if you care about that.