I just got back from a 350km road trip. On said trip, I decded tit would be a good idea to test out my cruise control. I noticed it did two weird things:

1. It would always cruise exactly 5km lower than where I set it at. Say I'm cruising at 100km/h, I set the cruise, and let my foot off the gas. The truck would always slow down to 105km/h before the cruise kicked in. I tried it at several speeds, with the same result.

2. This is the fun one, with the cruise control engaged, the truck will NOT upshift. I'm cruising in OD, when I reach a slight incline. The cruise give it some gas, enough to downshift into 3rd. The truck accelerates up to speed, the road levels off, but the truck stays in 3rd, hovering say at 4k. The second I hit coast, or turn off the cruise, it goes back into OD.

I actually had an interesting experience where the cruise was set a little high, and I came up to a hill. The truck downshifted into 3rd, then accelerated up to about where it would shift into OD, but instead, it downshifted again, into 2nd, and over-revved the motor.

Why is my cruise control on crack?

 

I think I have just about the same problem with my cruise control... I don't really think too much about it... I just make sure that my foot is ready to hit the break, or my thumb hit the cancel button when it over-revs going up a hill lol

 

The first thing I'd check is the cable adjustments on the throttle body. Both for the CC and the auto tranny kickdown cable. The FSM shows how to adjust both.

 

Good call. The cruise is vacuum operated, so there is always some little fluctuations on hills and such, but as the Goat said, any of the cables that are out of adjustment will make the problem worse.

 

along the same lines, my cruise (5 speed) randomly shuts off on flat surfaces... usually only does it when i have it set at 55mph... any ideas??
the cable is not loose, and everything seems ok...

 

check the vacuum system. in the end i removed my CC because it would flux to much for my liking. i travelled 7000kms with no cruise because it did not work right. and i was not hurting afterwords.

 

The brake light switch at the pedal will shut it down. If that switch is out of adjustment, it'll shut it down. I've also seen a bad brake light bulb do it too (for real)

 

i don't use mine anyways, you could remove it and then have room for an air compressor or something.

 

That is very true! it gave me amazing extra space under my hood! and if you did a cold air intake, you can move the intake to the CC's old location then place a 2nd battery where the intake used to be.

That was my original intention but then i found my 3.4L so i did not want to go through the trouble if i am just taking it out anyway.

 

i have a huge problem with my cruise control. just recently out of the blue, ever time i turn on cruise control it automatically turns itself off, and wont allow me to turn it back on. Any suggestions, let us know

cheers
guys

 

is it possible that the vacume lines could b reversed and make the controls backwards? ???anyone?

 

you may want to look into the solenoids if and when you drop the pan. test them out and make sure they are working properly. you could try disconnecting the battery to clear the stored codes. ive done that with mine on occasion when my cruise light blinks and wont engage.

mt goat has the best suggestion to try first, after all, we all get a bit out of adjustment with age!

keep us posted.

lee

 

Yep, or if the switch on the clutch pedal is too far away from the pedal arm, that was the problem with mine. Hit a little bump in the road and the clutch pedal would jiggle a little and that would kick the c/c off (of course would not apply to an automatic). Sign that one of these two problems is happening is if the c/c will resume the previous speed or not.

I also had a problem with a poor ground connection at the main cab ground point, located close by the c/c module. Nothing was loose, but I pulled all the ground wires, wire brushes the ends and sanded the sheet metal under the screw to clean it all up. What would happen there is the c/c would cut off and would not resume the old speed, since in effect it had been shut off and turned back on.

Mine also drops a few MPH from where it is set. Being an all digital unit, there is no internal gain and offset adjustment like the older analog c/c units used to have. I have been contemplating retrofitting an Audiovox c/c into the my '85 as it is fully adjustable. I run one in my daily driver and it is a much better unit.

I have added a vacuum cannister for mine that helps hold the speed under high load conditions.

 

That's interesting Roger, is that like an air version of a capacitor?

 

Sort of like that. Has a check valve in the inlet line to isolate it if the intake vacuum drops too low. Similar thing is used for the ADD actuators as I recall.

 

Yeah I still have my ADD vacuum cannister up in the attic somewhere.

 

That vacuum canister idea is interesting. I would assume that because my vehicle is a turbo, there is already some sort of vacuum canister in place for the cruise control. I'll check the check valves on it, and maybe add another canister.

 

I have a similar problem. My cruise control sometimes works and sometimes doesn't. Then it will blink at me and go off and not come back on until I turn off the truck then turn it back on again. I am thinking it has something to do with my knock sensor that has been going bad for the past 3 years. I think it is leaning out the engine too much. I would fix it if it wasn't such a PITA to get to and so expensive.

I have also noticed that ever since I put in LED replacement brake/tail light bulbs that the C/C kicks off when I turn my turn signals on. That I think is my laziness in not buying the resistors they sell to install with the LED lights. That would probably fix the prob. I'll try each of these tips and see which one fixes or reduces the problem/s.

 

Thanks for that idea, I'll check it out.

 

Having CC issues? I just fixed mine with a new brake pedal switch. It worked intermittently unless I flicked the brake pedal a couple times before setting it.

By the way, this is a 6 year old thread...