engine computer won't let my Liberty engine-brake

downsdou · **Posted:** Fri Sep 22, 2006 10:49 pm

My dealer thinks I'm nuts about this, but I kid you not:

'05 3.7L w/ 4 speed auto: when I shift down, if the engine is at less than 2800 rpm (once shifted into 2nd or 3rd gear) or less than 3700 rpm (once shifted into 1st gear), the computer *applies throttle* until the engine reaches that speed, then releases the throttle and the engine starts to break the vehicle.

I know, I know, you're thinking, "You idiot, that little 3.7L just can't hold the Jeep back so the truck is speeding up on its own." That's what my dealer thinks. Give me some credit -- not an idiot, and I know the difference between a hill too steep for the engine to slow the truck versus a gentle hill where if you just let off the gas, the truck slows down. Unless you downshift it, which makes the computer hit the gas.

It gets better: Say I'm doing about 20 and shift down to 1st. This is about 2800 rpm. The truck speeds up 'til the engine hits 3700 rpm, which is about 30 mph (which utterly defeats the purpose of shifting down to engine break, not to mention scaring my passengers to death). Then the computer lets off the throttle and the truck slows decisively, down, down, down, all the way to 1200 rpm and 10 mph or so. Then the computer hits the gas again (no foot anywhere close to the throttle) and the engine zings back up to 3700, when it lets off again. I've seen it do this cycle 5 times before I ran out of hill.

I can't get a dealer tech to sit in the truck long enough to actually get the truck in a place where it does this. They just check the computer and tell me, operating as designed.

Of course, it also does this in low range, which means, you guessed it, I can't creep/engine-brake at all on hills unless I'm willing to let it get over 10 mph before the computer takes its darn foot off the throttle. Again, if I need to actually crawl it in 4-low, I can't afford to be ripping along at 10 mph.

Anyone ever heard of anything like this? I've been reading all over these boards and haven't seen a similar story.

Jeepjeepster · **Posted:** Fri Sep 22, 2006 11:02 pm

Yup, thats correct. We have had tons of discussions about this trying to figure out why its like this... :wink:

jason thompson · **Posted:** Fri Sep 22, 2006 11:17 pm

never heard of such a thing my self and infact I know that our Kj does better at engine breaking than our TJ
I would try to dissconect the batt for a few min.s and see if it gets better

I am not sure how you wheel but for us we just put it in fisrt & 4lo and stay there
when you put it in first it should almost lock up fully if the engine is reving and slowing I think something is wrong

and as far as 3700 rpm :shock:

we never see 3700 rpm off road and almost never on road unless I realy get on it

FreedomKJ · **Posted:** Fri Sep 22, 2006 11:30 pm

Mine certainly doesn't do that. If your dealer's service deparment isn't cooperation take it up with the general manager, and then the district manager if you still have trouble.

streetKJ · **Posted:** Sat Sep 23, 2006 5:04 am

Ask for an ECU reflash.

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

Mine works extremely well. Which transmission do you have? I have the 45RFE.

Eddo · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 1214

Doesnt work really all the well with the newer 42RLE, but it does work to some extent. Also seems to work a little better in 4-low, but not nearly as good as some other automatic/engine combos.

Mine definitely doesnt apply throttle during engine braking.

Jeepjeepster · **Posted:** Sat Sep 23, 2006 11:17 am

Eddo wrote:

Doesnt work really all the well with the newer 42RLE, but it does work to some extent. Also seems to work a little better in 4-low, but not nearly as good as some other automatic/engine combos.

Mine definitely doesnt apply throttle during engine braking.

Thanks for agreeing with me eddo.

Mine doesnt give it gas, but Ive seen over 3500rpms going down a hill in 2wd and 1st gear. In 4low, it does hold it back, but on steep hills it will speed up alittle to fast. My brothers cherokee and our grand cherokee holds like nothing else. Its a dead crawl in those things.

downsdou · **Posted:** Sat Sep 23, 2006 11:31 am

Thanks for the confirmation that it's a problem rather than a design, folks. It's done it since factory and only has 17,000 on it (and no drivetrain mods), so it was hard to tell at first -- it's the 42RLE, which already has a slushbox TC (which I think is what you're feeling, too, Addict), so took me awhile to really decide it's broke.

I've been wondering about an ECU reflash -- does seem to be engine control rather than trans control, though they'll talk to each other, like when the cruise shifts down the trans on grades. And thanks for the advice on the stealership gen manager -- I haven't gotten out of the service dept. yet. Go spend some quality time banging heads, I guess....

Oh -- and tell me about not wanting to see the revs at 3700 off-road! Argh!

Marlon_JBT · **Posted:** Sat Sep 23, 2006 11:33 am

My sister's doesn't do that... neither did my old Jeep. Something is wrong here.

dirtykj · **Posted:** Sat Sep 23, 2006 1:15 pm

jason thompson wrote:

never heard of such a thing my self and infact I know that our Kj does better at engine breaking than our TJ

This "no engine braking worth a darn" is for > 03 KJ's IIRC.

I know that my '05 exhibits this same behaviour as well. Also, if my speed is too fast, the KJ will not downshift into lower gears (I suppose that makes sense).

dirtykj · **Posted:** Sat Sep 23, 2006 1:16 pm

Marlon_JBT wrote:

My sister's doesn't do that... neither did my old Jeep. Something is wrong here.

Possible you haven't found a steep-enough hill

mb818 · **Posted:** Sun Sep 24, 2006 10:55 pm

driving in the mountains this summer, we found our '05 to engine-brake better with the cruise control on than off... it was like free-wheeling downhill when manually downshifting without the cruise on... but with the cruise set, the computer downshifted and did a nice job holding the speed on steep downgrades... kinda wierd...

Mark

streetKJ · **Posted:** Sun Sep 24, 2006 11:25 pm

mb818 wrote:

driving in the mountains this summer, we found our '05 to engine-brake better with the cruise control on than off... it was like free-wheeling downhill when manually downshifting without the cruise on... but with the cruise set, the computer downshifted and did a nice job holding the speed on steep downgrades... kinda wierd...

Mark

Doesn't cruise control not work under 40mph?

2006KJSPORT4x4 · **Posted:** Sun Sep 24, 2006 11:58 pm

35+ Cruise Control works....or at least on my 05 it was like that...my 06 doesn't have Cruise Control....yet...

Sean · **Posted:** Mon Sep 25, 2006 4:19 pm

not sure if this is related, but when i hold down the coast button when running cruise on the freeway, at say 75-80mph... it will do something to cause the RPMS to scream around 3500, then after about five seconds it will become normal again, all while I am holding the coast button (or whatever it is called) while using cruise.

Jeepjeepster · **Posted:** Tue Sep 26, 2006 11:26 am

Sean wrote:

not sure if this is related, but when i hold down the coast button when running cruise on the freeway, at say 75-80mph... it will do something to cause the RPMS to scream around 3500, then after about five seconds it will become normal again, all while I am holding the coast button (or whatever it is called) while using cruise.

It downshifts into 3rd then locks the torque if you keep holding it. It should slow you down purty quick if you keep holding it. After you release it will pick back up at whatever speed you let off the coast button at. :wink:

KY Liberty · **Joined:** Sat Jul 09, 2005 1:46 pm **Posts:** 1195

I found this on another forum. Thought it might be useful.

http://dodgeram.info/tsb/2006/21-002-06.htm

engine computer won't let my Liberty engine-brake

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