Cruise control won't accelerate or decelerate, but works otherwise

[iroc86]

I think I'm having an issue with the cruise control in my '89 Grand Wagoneer, but I'm not sure what the problem might be. When cruise is engaged, I can't increase (or decrease) my speed using the buttons on the turn signal stalk. I need to completely turn off the system, accelerate (or decelerate) to the new speed, and press the engagement button again. Besides this issue, the cruise control system works great.

For example, if I'm cruising along at 45 mph and hold the R/A button until my vehicle reaches 50 mph, the Jeep will decelerate back down to 45 mph as soon as I release R/A. The same thing happens with the Decel/Engagement button, except in reverse.

Every other cruise system I've used has worked differently... tap R/A to increase by 1 mph, or tap Decel/Engagement to decrease by 1 mph.

I've already swapped out the yellow cruise control box with another one, to no avail. Do I have a problem or is this just the way that AMC designed it?

[jeepjerry]

I think your lucky that it works that much... ...ive never had an AMC or Jeep that the cruise worked on.....

[BGW]

The same thing happens with the Decel/Engagement button, except in reverse.

Haha I read this really fast and for a second there I thought you were using the cruise control while driving in reverse!

Here is what the manual states:

"To Set Cruise Control
Accelerate to the desired speed, turn the CRUISE switch
to ON, push in the engagement button, then release it.
Take your foot off the accelerator pedal and the set
speed will be maintained, with some variations when
going up or down hills.

To reset Cruise Control to a faster speed, accelerate to
faster speed using the accelerator pedal or R/A
(Resume/Accelerate) button, then push in the engage-
ment button and release it. To reset to a slower speed,
push in the button all the way and hold it there until your
Jeep vehicle slows to the desired speed, then release the
button.

To disengage Cruise Control, apply the brakes lightly,
turn the control to OFF. When the ignition switch is OFF,
the Cruise Control is also disengaged."

Mine works like that, and I think the cruise control was the same in the later model years.

I would think the yellow box would be your problem, but since you've already replaced it, I don't really know.

[iroc86]

Yeah, I guess I should be lucky that it even maintains the speed.

Thanks for the excerpt from the owner's manual, BGW. It seems like my system sort of works the way it's supposed to, except for the hold-to-decelerate bit. Hmm...

[jeeper54]

Strangely enough, mine works too. Except that when I engage it, it will speed up about 5 mph.

[Mark Wilde]

When using the buttons to accelerate/decelerate, you have to push the engagement button to lock in the speed. At least I have to on mine. Mine also speeds up 4-5 MPH when engaged. Sucks having to guesstimate, but at least it works!

[iroc86]

I played around with the cruise control some more this morning. Based on what everyone here is saying, I think it's working the way it's supposed to (though different than what I'm used to on every other car I've owned -- it IS a FSJ, after all!).

Mine also seems to speed up about 3-4 mph when cruise is engaged. I've found that to accelerate a small amount, I can press the Decel/Engagement button due to the 3-4 mph offset. Counterintuitive, yes, but it seems to work. Similarly, deceleration requires slowing 3-4 mph below the intended speed and then letting go of the button, which lets the vehicle "catch up" to the intended speed.

From what I've read, I think the 3-4 mph discrepancy could be tweaked by adjusting the Centering control on the cruise box. I might try it and see what happens.