I am wondering what my cruise control does. It is working, but each time u engage it and set the speed, it basically skyrockets to 75MPH, so u have play with it to get it to the correct speed, by decel button and u have to hold it for quite a while. It iritates me, I hate things not working properly.

 

Not sure how you're engaging it, but for me just ON, then hold the SET butting for about 5 seconds while maintaining the speed you want, then release the accelerator.
For me the less steady you are with the pedal the longer it takes for the system to "save" that speed setting.

But if you're doing that and it always skyrockets up to 75, then you've got two problems:
1. I can't help you, but other members smarter than me can
2. You have lots of power and that's a good problem to have.

 

Well it is not the lots of power issue. Well, I maintain speed, press the on button and it engages and goes full throttle to 75, where it stays, no matter what was the speed at the time of the engagement. When I press the decel, it slows but goes back to 75 after release, so I just hold it long enough to go 10 miles slower then I want the cruise control to maintain, release it, it raises 10mph and stays.

 

Try this:
1. Press the "On" button.
2. Once you are at the speed you want, hold the "coast" button for 5 seconds, then release.
3. Release your foot off the accelerator and the cruise should kick in.

I /never/ use the "set/accel" button to engage it; I use it only to, well, accelerate.

 

Interesting

 

my 88 started doing that after the first injector pump change. i finally tracked it down to an improperly adjusted cruise control unit to injector pump cable

 

I have not thought about this, I just thought to get rid of the play in the cable. Good point tjc. But I have not touched anything, just observed. I thought it is ruled by the speedo cable, so the adjusting the cable is irelevant. But have to look at it closely.

 

if i remember correctly it need just a tiny bit of slack otherwise it will take off like that.
let me see if i can find the adjustment procedure in the service manual.

 

I'd be interested in this too. Mine was so loose that it wouldn't go above 1/3 throttle(and therefor would lose power going up a hill). I shimmed out the housing on the actuator to take up some slack, and now it goes to half throttle... enough to maintain 60+ up a hill.
But there's still a ton of slack to be adjusted out.

 

i can't scan the manual page for some reason, my scanner is not cooperating today. the book calls for basically no slack at all.
the following adjustment is done at the injector pump side of the cable.

remove the adjuster retainer clip from the mounting tab.
pull the adjuster until a slight tension is felt without increasing idle rpm.
insert adjuster retainer clip slowly until engagement is felt and then push down-word until it locks into position.

 

This is very interesting. Does anyone know what these trucks use to provide speed information to the cruise module since the speedometer is mechanical? And what is the point of holding the set button for 5 seconds while maintaining speed?

When I drove the truck to the port in LA my experience of it was that pressing set/accel would give a full throttle burst to about +7mph above your current speed. Does not sound like a big deal but it is quite alarming especially if you don't know the acceleration will eventually subside. Any additional touch to the set/accel button would add another +7mph or so in the same full throttle fashion. I tried the decel button but I must not have held it long enough as the speed would climb right back when I let go of it. I continued to use it on the open road, but I would slow down to about 7mph less than I wanted, then press the set button and let it take off. If there was very much traffic at all that became completely impractical and a nuisance. I really hope you get it fixed. It does sound like it could be a cable adjustment problem, be sure to post the details if you get it figured out.

 

a two-wire sender in-line with the speedo cable where it comes out of the transmission or transfer case.
So that the computer knows it's a valid input and not a random button press/noise.
Time may vary. I know that I have to hold it for at least a couple seconds.

Just try it out. If it works, it should work well. But I only have a working cruise control on my tan 88, none of the other same-vintage trucks have it work at all, so I don't know if this works due to a quirk or not.

 

So is there a pulse generator there? Mine has one but I thought it was part of the GVOD. You have (a GVOD) also, does it use the same pulse generator for both?

 

No, there's two. The Factory one is after the GVOD sender(the large shiny one), and it's pretty small -- maby 1" in diameter and the same long.

In my case, I have the GVOD sender disabled(GVOD computer as well; it's just hooked to a switch on my gearshift).

 

Thanks, mine is definitely missing the cruise sensor then. More junkyard homework to fix the PO's hackwork. I will send you a PM about your GVOD computer delete... I am curious about this but I don't want to hijack this thread any worse than I already have.