do these automatically idle up/accelerate in 4 low to climb over obstacles?

[ShadowsPapa]

while up against a curb, took my foot off of the brake, and waited. It went from about an 800rpm idle to about 1000rpm and tried to climb the curb. FYI, it maintained the higher rpm the whole time, but did not climb over(about a 6" obstacle).

Mine finally backed down again once it decided it couldn't make it over the 4x4s. It took a few seconds, but I watched as the RPM eventually went back down.

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[Lunentucker]

Just try with brake on and you are right. No RPM gain
Put is there any way to turn this off
Thanks

Brake = no go
No brake = go
Keep at least one hand on the steering wheel too.

 

[ShadowsPapa]

Brake = no go
No brake = go
Keep at least one hand on the steering wheel too.

Man, where's your sense of adventure?!?

 

[Artsifrtsi]

My '05 TJ (6sp manual X trim)ups the idle when crawling without putting foot on throttle, and without an electric throttle. Does it in 2, 4H, and 4L. It's all about keeping the motor from lagging/dying. At a stop, if you slowly let the clutch out, you'll see the RPM drop, then it'll ramp back up to prevent a stall.

Definitely not a new thing...

 

[ShadowsPapa]

My '05 TJ (6sp manual X trim)ups the idle when crawling without putting foot on throttle, and without an electric throttle. Does it in 2, 4H, and 4L. It's all about keeping the motor from lagging/dying. At a stop, if you slowly let the clutch out, you'll see the RPM drop, then it'll ramp back up to prevent a stall.

Definitely not a new thing...

IS it "upping the idle" or simply maintaining the idle?
Upping means if it idles at 800 normally, then it actually INCREASES idle speed to above 800 RPM.
Maintaining means if it idles at 800 and you start pulling it down, it tries to maintain that 800 RPM but doesn't rise above it.
Without an electronic/motorized throttle body, all it can do is adjust timing and fuel injectors for the load.
But this is very different from that.
This actually increases base idle speed, and then REDUCES it again. Nothing at all about preventing a stall.
If you run up against blocks in 4L and then take your foot off the brake and gas, you can watch it ramp up 200 to 300 RPM - then slowly back down. That's hardly doing something to prevent a stall because if you wait long enough, the idle actually returns back down to 800 - yet you are still in the same set of circumstances.
There's no need to prevent a stall because this only happens with foot OFF the brake, yet with foot ON the brake, you have the same exact load, the same exact RPM. There's no "preventing a stall" to this.
If it was, then every time you came to a stop, the engine RPM would climb - it doesn't.
This climbs only when you take your foot off the brake.
These, as with older engines, always maintain idle speed under a load - this is not that. This is an increase, then a decrease.

Bottom line - when you let the engine settle to a warm curb idle at about 750-800, then hold the brake and put it in gear, it maintains that 750-800 RPM idle speed.
You put it in 4L, put it in gear, foot on brake, it idles at 800.
Run it up against blocks, foot on brake, idles at 800. Take foot off brake, it starts out at that same 800, then slowly ramps up to roughly 1,000.
So, what's the difference between brake on and load on the engine vs. blocks stopping it from rolling - same EXACT load on the engine -the truck is stopped and it's in gear, idling.
It doesn't jump, it ramps up.
There is zero difference between sitting in gear blocked by 4x4s compared to sitting in gear being held by by the brakes and yet with the former, it ramps idle up.
There is no need for it to try to maintain a stall.
Think really hard about that - because you are saying when you come to a stop light, it's going to stall unless it changes idle RPM - but it doesn't, it maintains the 800. So why does it then increase the RPM when you take your foot off the brake with it stopped by an obstacle? There's no more load on the engine than when you have foot on the brake.
This isn't that.
This is a very different situation.
And we can't compare a stick to an automatic with this feature - apples and oranges.
You can't stall an automatic - the torque converter prevents it.

 

[Artsifrtsi]

It's king of a combination. It sees the load, bumps the idle high enough to prevent a stall, and then drops. In 4L, it really is noticeable, and sometimes un-nerving as you'd expect a little drop in speed in certain scenarios, but it will increase and can buck on a tall enough obstacle.

 

[ShadowsPapa]

Dan - I found reference to it with the JK - seems it was introduced with the JK/Wrangler -

A guy with a TJ was complaining about it.
It's a crawl feature, and some of the tuners take advantage of it and allow tweaks.

It's for low RPM crawling over obstacles where using the foot could cause too fast a change in speed. It's specifically for crawling over rough ground.

You nailed it - it's a feature for crawling, started with the JK apparently. Only in 4L from all the stuff I've read this AM -
Put it in 4L, leave your feet off the pedals and it slowly crawls (but with limits on the high side of the RPM like I found, it doesn't seem to go over a certain RPM)
What the other guys with the JKs were saying is that if the obstacle is large enough, it won't get over it (like my testing - it's got limits) but for a slow controlled crawl over rough stuff within those limits, it's a feature for crawling.
As long as you know it's there, and are smart - it shouldn't cause trouble on ramps as you should always be hovering over that brake pedal anyway in such cases.
This isn't really connected to anything else, and I suspect if you used the automatic's manual mode, you'd have some nice control over it.
It's about crawling, KEEPING up forward motion - not about not stalling as nothing with an automatic is going to stall anyway. They just don't, no matter how old, even with carburetors.
I've found other references where tuners have given more control over it and taken advantage of the feature. I found people who just got into the JK from other Jeeps complaining about it - then JK owners explaining it.

PS - you can't stall an automatic - it's not about stalling.

 

[WILDHOBO]

Dan - I found reference to it with the JK - seems it was introduced with the JK/Wrangler -

A guy with a TJ was complaining about it.
It's a crawl feature, and some of the tuners take advantage of it and allow tweaks.

It's for low RPM crawling over obstacles where using the foot could cause too fast a change in speed. It's specifically for crawling over rough ground.

You nailed it - it's a feature for crawling, started with the JK apparently. Only in 4L from all the stuff I've read this AM -
Put it in 4L, leave your feet off the pedals and it slowly crawls (but with limits on the high side of the RPM like I found, it doesn't seem to go over a certain RPM)
What the other guys with the JKs were saying is that if the obstacle is large enough, it won't get over it (like my testing - it's got limits) but for a slow controlled crawl over rough stuff within those limits, it's a feature for crawling.
As long as you know it's there, and are smart - it shouldn't cause trouble on ramps as you should always be hovering over that brake pedal anyway in such cases.
This isn't really connected to anything else, and I suspect if you used the automatic's manual mode, you'd have some nice control over it.
It's about crawling, KEEPING up forward motion - not about not stalling as nothing with an automatic is going to stall anyway. They just don't, no matter how old, even with carburetors.
I've found other references where tuners have given more control over it and taken advantage of the feature. I found people who just got into the JK from other Jeeps complaining about it - then JK owners explaining it.

PS - you can't stall an automatic - it's not about stalling.

Good research. Nice find. That’s exactly how it works in the wild. And depending on your gear ratio, it works better or not as well. My crawl ratio is 96:1, so it works REALLY well.

I agree that the feature isn’t related to stalling, but you can stall an automatic on tough terrain. I’ve done it with mine multiple times when going carefully up larger obstacles and controlling the throttle to keep the pace to inches per second. It happens, but not often. I’d say a dozen times in two years. But never on the road. Only rock crawling in tough spots. And even then it’s rare.

 

[ShadowsPapa]

Good research. Nice find. That’s exactly how it works in the wild. And depending on your gear ratio, it works better or not as well. My crawl ratio is 96:1, so it works REALLY well.

I agree that the feature isn’t related to stalling, but you can stall an automatic on tough terrain. I’ve done it with mine multiple times when going carefully up larger obstacles and controlling the throttle to keep the pace to inches per second. It happens, but not often. I’d say a dozen times in two years. But never on the road. Only rock crawling in tough spots. And even then it’s rare.

You are literally killing the engine ahead of a torque converter, which has a stall speed of at least 1500 - 2000 RPM?
Engine stall is engine dying, and since the engine isn't directly connected to anything - that should be really really hard to accomplish.
Heck, these guys pulling stumps with pickups aren't killing the engine.

 

[WILDHOBO]

You are literally killing the engine ahead of a torque converter, which has a stall speed of at least 1500 - 2000 RPM?
Engine stall is engine dying, and since the engine isn't directly connected to anything - that should be really really hard to accomplish.
Heck, these guys pulling stumps with pickups aren't killing the engine.

I don’t know why it happens, but it occasionally does. I don’t know at what rpm’s though. Always on an ascent, and almost always when going VERY slowly over rock obstacles. Again, it’s only happened maybe 12 times in 2 years of heavy wheeling, and never on road.

 

[ShadowsPapa]

I don’t know why it happens, but it occasionally does. I don’t know at what rpm’s though. Always on an ascent, and almost always when going VERY slowly over rock obstacles. Again, it’s only happened maybe 12 times in 2 years of heavy wheeling, and never on road.

Must be related to the converter's locking system. Would love to be monitoring that with software during such times when you are climbing like that.

 

[WILDHOBO]

Must be related to the converter's locking system. Would love to be monitoring that with software during such times when you are climbing like that.

Is so rare, and always very gentle rpm conditions. It usually surprises me and I just laugh. From quiet, to quieter. I’d say I’ll pay attention next time, but it doesn’t happen a lot.

 

[Jefe1018]

I guess I never noticed this because my eco diesel just idles up everything in 2H when it’s not in the shop. /s

 

[willys 41]

Try this
Put it in 4W low
pull up to a curb
You will find that as soon as you hit the curb the idle will go up .Put if you lightly apply the brakes the idle will go back to normal
If you want full control crawling over something you will need to have slight pressure on the brake pedal

 

[ShadowsPapa]

Try this
Put it in 4W low
pull up to a curb
You will find that as soon as you hit the curb the idle will go up .Put if you lightly apply the brakes the idle will go back to normal
If you want full control crawling over something you will need to have slight pressure on the brake pedal

That's what's been said - but the feature is for better control over crawling by NOT using the brake or throttle pedal. I can see more to it now and it makes sense as it can control crawling, especially ascent, without breaking the tires loose.
I may end up using this myself in the WINTER one of these days, especially if needing to pull my trailer out in the middle of winter in the snow and ice.

In my testing, a couple of pages back in this thread, the idle doesn't go up "as soon as you hit the curb" but ramped up slowly until it overcame the obstacle then ramped back down a bit more quickly. The ramp up of RPM was slow, the ramp down not instant, but not AS slow as up.
https://www.jeepgladiatorforum.com/...limb-over-obstacles.70406/page-4#post-1151971

It only does this is you are not over-riding with the pedals.

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