cruise control

My cruise control hasn't worked since I've owned my 89 xj 5speed 4.o. so I'm looking for advice on what to check.

Thanks for any help.

the actuator on the throttle body is vacuum controlled. Apparently vaccum leaks make it act funny.
There should be a yellow box under your steering column, that's the cruise box. I've seen a few pictures of burnt diodes on the insides.

There is also a switch on the brake pedal you might check. The switch can be disassembled and cleaned if needed. It also has a vacumn line to it from the actuator. The switch releases the vacumn on the actuator just in case the cruise control goes haywire.

Just spent 10 days fixing my cruise control in anticipation of a cross country trip, so of course I think I'm an expert now.

The first thing I would check is the fuse. It's not part of the regular fuse block under the driver's side dash, but it's in a separate connector nearby.

After that, I noticed that the controller box (the yellow box under the driver's side dash) is often improperly adjusted.

So as long as the servo holds vacuum then it's probably an electrical problem?Any tips on adjusting the "yellow box"?

If your cruise control is not working then it is not an adjustment issue. You should not start in that end. I have have had 3 faults with my cruise on my 89.

The first was a vacuum leak at the bottle in the bumper. The vacuum line was loose.
Second time the switch with the vacuum fitting on the brake was loose. To find it I put a small compressor on the line from the actuator that goes through the firewall. I then listened for the hissing sound of a leak. Pushed the switch into position so there was no leak.
Third time there was a broken wire by the brake switch.

To find the fault I would go this route:
First check that you have vacuum present at the actuator.
Check that both brake lamps are working.
Check that the vacuum on the brakeswitch are holding vacuum.

Get a schematic.
Disconnect the connector from the yellow box.
Take the following measurements at the connector:
1.use a voltmeter and check that there is voltage present.
2. use a ohm meter and check that the switches on the steering coloum works.
3. Check the brake switch by the connector.
4. Check the pulse encoder (speed sensor). Put the meter into Hertz and drive around the block. The sensor gives out 6 pulses per revolution. You should get around 40-60 hz at normal city speed.

If all these are ok, then may be the yellow box is shot.

regards
Torfinn

I had multiple problems, as well, and the last problem I had WAS a misadjustment of the AMC Module. The sensitivity pot was turned fully clockwise, and the cruise wouldn't engage above 45 mph. I adjusted it down, and no further problems.

Incidentally, my other problems were a leaky vacuum bottle, a blown fuse, and misadjusted clutch and brake switches.

To eliminate the possibility of those switches, it's quite easy to bypass them with a wire at their connectors. Of course, keep in mind that hitting the clutch or brake won't disengage the cruise control in that condition, so be careful.

As far as adjusting the yellow box, I set the centering and low speed pots to about 10 o'clock and the sensitivity to the center of its travel.

Poked around a little today and I found that the clutch peddle switch was gone(damn previous owners)....so I just cut the connector and routed the wire so that the brake switch completes/breaks the circuit.The 4 amp fuse is good and There is vacuum present at the servo and the brake lights work.The vacuum connections are good and the vacuum tank is new not leaking.What kind of adjustment can be done to the brake switch??

I looked for this vacuum switch at the brake peddle but didn't see anything that looked like a vac switch.....anyone have a pic of it?

Thanks for all the help so far,I'm a rookie when it comes to cruise control.....

http://mysite.verizon.net/~chris83803/jeep/cruise_switch.jpg (291k image)

The button faces forward and is pushed in when the brake is not pressed. Pressing the button in blocks the vacumn line and connects the two electrical contacts. Part of the mounting bracket is missing in the picture. If you need to clean it, the switch comes apart by pressing the little tabs. This switch controls both the cruise and sends a signal to the tranny computer if you have an AW4 (tells it to unlock the TC).

lawsoncl said:

http://mysite.verizon.net/~chris83803/jeep/cruise_switch.jpg (291k image)

The button faces forward and is pushed in when the brake is not pressed. Pressing the button in blocks the vacumn line and connects the two electrical contacts. Part of the mounting bracket is missing in the picture. If you need to clean it, the switch comes apart by pressing the little tabs. This switch controls both the cruise and sends a signal to the tranny computer if you have an AW4 (tells it to unlock the TC).

Click to expand...

Forgot to mention that one side of the switch goes to ground and the other is a lightblue/yellow wire.

so I just cut the connector and routed the wire so that the brake switch completes/breaks the circuit.

Click to expand...

Not the best idea. When you step on the clutch to downshift or to panic stop, your engine will rev up trying to maintain speed. There is a reason the factory put the switch on the clutch in manual tranny vehicles. I suggest going to the boneyard and getting the parts to do the job correctly.

Spudboy said:

Not the best idea. When you step on the clutch to downshift or to panic stop, your engine will rev up trying to maintain speed. There is a reason the factory put the switch on the clutch in manual tranny vehicles. I suggest going to the boneyard and getting the parts to do the job correctly.

Click to expand...

... if for no other reason than all the witnesses at the accident scene will tell the officer that you "gunned it" and ran into the vehicle in front of you on purpose...

Den

lawsoncl said:

Forgot to mention that one side of the switch goes to ground and the other is a lightblue/yellow wire.

Click to expand...

Thanks for all the help,Lawson.

I didn't see anything that resembles that switch around the brake peddle....maybe for some reason the p.o ditched that along with the clutch switch....at least they plugged the vac line up good because I don't hear any hissing under there.Time to go back to the yard,I'm practically on a first name basis there lately.So will a vac switch from an auto work on a 5 speed?How hard is it to get out?

Wait a minuet.I just looked at that pic again and it looks like the same connector style that is on the end of a wire hanging under my dash,always wondered what the connector plugged into.I bet thats it.

I'm pretty sure the switch from the auto is the same as the switch for the manual. The wiring schematic shows both the wire from the trans computer and the cruise going to the same spot on the switch. When I was at the pull-n-save, the switch was present on most of the auto XJs and the vacumn line just wasn't connected. It was a pita to get out, btw.

I didn't use the switch when I swapped in the auto. Instead I grabbed a relay out of the parts pile in my garage. I wired it to the brake light switch so that the trans/cruise wire was normally grounded. Hitting the brakes would click the relay and break the ground connection.