jeep question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

71chevytruckguy · 01-25-2008, 01:08 PM

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.

bad_turbo · 01-25-2008, 02:07 PM

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

Chris27 · 01-27-2008, 04:30 AM

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.

vtblazer · 01-27-2008, 04:56 AM

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?

*FormerMember* · 01-28-2008, 06:10 AM

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.

71chevytruckguy · 02-03-2008, 03:56 PM

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.

*FormerMember* · 02-03-2008, 10:48 PM

Quote:

Originally Posted by 71chevytruckguy

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.

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

Blue_71 · 02-04-2008, 08:06 AM

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

01-25-2008, 01:08 PM	#1
71chevytruckguy Registered User Join Date: Jul 2005 Location: Kernersville, NC Posts: 599	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. __________________ its a work in progess. 71 c-10 lwb, in the middle of frame off restoration. 69 c-10 swb, drag truck, 406 sbc, balanced, comp 292 cam, ported, polished, gasket matched, and bowl blended pro comp 210cc heads, 2.02/1.60 ferrea valves,1.6 roller rockers, re curved hei with msd 6al box, 2-step rev limter, accel 300+ wires, ported victor jr intake, holley 750 double pumper carb, dynomax 1 5/8 headers, 4 spd munci m-20 with super case and iron midplate, mr. gasket vertigate shifter, 5.38 pro gears with full spool, 33 spline moser axles and c-clip elimators, line-loc, 5 gal fuel cell, holley blue pump. 7.807 @ 88.37mph 1.60 60FT 80 g-20 van, tow rig, cammed 305, th350, 10 bolt 88 jeep wrangler, dd, 258, ax-15 swap, 4.5" lift, 33x12.50's, lockers, 3.55's

01-25-2008, 02:07 PM	#2
bad_turbo turbo enthusiast Join Date: Jan 2004 Location: carmichael, ca. Posts: 1,826	Re: jeep question not a mechanic, but would the vacuum on the trans have anything to do with it? __________________ "But daddy, I didn't hit them all with a stick"...what my 6 year old tells me when I pick him up from school early for fighting "

01-27-2008, 04:30 AM	#3
Chris27 Blazerless Join Date: Nov 2006 Location: Kelowna, BC, Canada Posts: 274	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. __________________ 72' K5 Blazer 4x4 350TBI/700R4/NP205 3/4 ton diffs. Daily driver. SOLD 69' Beaumont 388/700R4 11.70@116 77' Bronco, Wife's mall cruiser/poser 4x4. Capable but too pretty to go offroad.

01-27-2008, 04:56 AM	#4
vtblazer Registered User Join Date: Oct 2003 Location: Central Vermont Posts: 8,538	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?

01-28-2008, 06:10 AM	#5
FormerMember Account Suspended Join Date: Feb 2004 Posts: 3,051	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.

02-03-2008, 03:56 PM	#6
71chevytruckguy Registered User Join Date: Jul 2005 Location: Kernersville, NC Posts: 599	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. __________________ its a work in progess. 71 c-10 lwb, in the middle of frame off restoration. 69 c-10 swb, drag truck, 406 sbc, balanced, comp 292 cam, ported, polished, gasket matched, and bowl blended pro comp 210cc heads, 2.02/1.60 ferrea valves,1.6 roller rockers, re curved hei with msd 6al box, 2-step rev limter, accel 300+ wires, ported victor jr intake, holley 750 double pumper carb, dynomax 1 5/8 headers, 4 spd munci m-20 with super case and iron midplate, mr. gasket vertigate shifter, 5.38 pro gears with full spool, 33 spline moser axles and c-clip elimators, line-loc, 5 gal fuel cell, holley blue pump. 7.807 @ 88.37mph 1.60 60FT 80 g-20 van, tow rig, cammed 305, th350, 10 bolt 88 jeep wrangler, dd, 258, ax-15 swap, 4.5" lift, 33x12.50's, lockers, 3.55's



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