Scary Cruise Control

The cruise control in my '90 Laredo hadn't worked since I got the vehicle, and exploring around under the dash one day I discovered that the wire harness plug that goes into the back of the yellow cruise control computer was loose. I snapped the plug back in and now all aspects of the cruise control work perfectly--- except for one.

Especially at highway speeds, when I hit the button on the end of the stalk the system kicks in and immediately accelerates the vehicle to about five mph faster than I was driving when the button was pressed. Sometimes, especially it seems if I'm going up an inclined section of road when I engage it, the cruise control will nearly FLOOR the gas pedal, often causing the auto transmission to downshift. I recently installed a high-flow cat and Magnaflow muffler and you should hear this thing when it takes off like this! It's like hitting the afterburner in the Batmobile! It will then steady the speed out a good 5-6 mph higher than what I was travelling when the system was engaged and keep on keeping on all normal like.

My first question is this: is this behavior normal? I don't really have any way of knowing since I'm not the original owner of the vehicle.

I was hoping TPS might have something to do with it. I recently changed the way I adjust my TPS using a multimeter (went from setting output voltage at 4.2 volts to .83% of input voltage) and although now the Jeep runs better, this cruise control behavior remains unaffected.

Any ideas?

:revolver

the tps has no effect on the cruise for the 1990. it could possibly be a problem with the cruise switch wiring shorting inside the steering column giving the module the wrong signal.

there is also a centering adjustment on the side of the cruise module. if you turn the adjustment knob one direction or another while driving you can set the module to the speed when the button was released. you shouldnt have to turn it much.

Do you run bigger tires than stock and if so did you change your spedo gear ??

I recently put the MOPAR cruise kit in my '95 XJ, and it exhibits similar symptoms. If I hit the "accel" button on the cruise going up a slight grade at 55, it immediately drops into 3rd. It seems like the tranny (AX4) is partial to downshifting a little more readily than I would like. For example, in "1-2", it's almost always in 1st. I fixed that by putting in a "force 2nd gear" switch inspired by go-jeep.

My 99 with 68,000 miles has always done somthing like this also. When I set the cruise, the pedal always dips for a second and it accelerates to about 3-4 mph faster than where I hit 'set'. I thought this was normal.

marcus

RichP said:

Do you run bigger tires than stock and if so did you change your spedo gear ??

Click to expand...

it doesnt have anything to do with tire size. the cruise system is going to duplicate the speed it thinks it is going. if the output says 45mph, then it is going to do that. it doesnt know actual speed. only the speed the speed sensor says it is going.

My 1990 did exactly that- gained 6 kph from driving speed when setting the cruise control. A very slight adjustment to the centring screw on the cruise control box under the dash fixed it- after a couple of very slight adjustments, I now have it where it holds the same speed as before setting the cruise. Easy, free fix.