jeep question
 

been doin a bunch of work on a buddie's '89 jeep cheeroke. its got a 9" lift and 35x12.50's. has a very wierd problem that has me stumped so figured i'd ask yall. whenever it's in 4 low in reverse, the gas seem to hammer its self. its normal idles around 800rpm in gear, whenever its in 4 low in reverse only its the idle jumps up to 1500rpm and soon as u let off the brake sugres backwards, once its back in forward gears, its idles like and drives like normal. doesn't act up when its in 2wd and 4 high in reverse or any in forward gears, just 4 low reverse. any idea on why its doin that or how to fix it. i know its not a chevy but thanks. chris.

Re: jeep question
 

not a mechanic, but would the vacuum on the trans have anything to do with it?

Re: jeep question
 

Sounds like it's possesed! My girlfriends' Cherokee did the same thing, except it did it on the highway, peddle would go to the floor for no reason, even after we disconnected the cruise! Fortunatley it blew up before we had to fix it. :lol:

Re: jeep question
 

Bad mount maybe?
Allowing it to torque over when in low?

Something is moving enough to cause the issue and being in low, it will have more torque output than when in hi...dunno kinda guessing due to it being a jeep.

Does the throttle linkage physically move?

Here's three possible things could cause an RPM increase.
*Mechanicle movement of the throttle
*Change in vacuum (already mentioned)
*Timing changes somehow

Fill in some blanks please...
Carbed or injected?
Standard or auto tranny?
Hard linked throttle or cable?

Re: jeep question
 

Check the vacuum lines that engage the front axle. Willing to bet the lines or vacuum actuator is leaking.

Although I am not sure why it's doing it only in reverse, but it's a place to start.

I'd also check the throttle cable. Sounds like it's been shortened or it could be binding.

Is it the stock motor? I-4 or I-6? Probably the craptacular Renix FI. I'd check the computer and see if it's throwing codes.

Re: jeep question
 

thanks for the replies.

straight 6, injected, auto trans, front hubs are locked in all the time so no vacum lines to it. no throttle cable that i can see, all looks like linkage. just replaced the transmission mount so it no that shifting. it only acts up when it feels like it, no every time. real wierd. thanks, chris.

Re: jeep question
 

Look at the right hand side front axle tube. It should have a vacuum actuated coupling that disconnects the passenger side axleshaft.

Re: jeep question
 

any possability that the 4wd shifter and the auto shifter are crossing against something when its in 4 low and reverse? a wire, anything that could pull on the throttle