1984 GM Cruise control trouble shooting instructions needed

[klwinter2]

I can not figure out why my cruise will not activate.
It has vacuum up to the actuator and varying voltages from the steering wheel buttons to the control unit..

I have a wiring diagram and have tested everything I can think of.

Does anyone have the actual trouble shooting process diagram?

The only think I have not tested in the VSS... I dont know how to test it..

Kenneth

[sly]

I'll grab a spare I have on hand and see if I can figure a simple way to test it without an oscilloscope.

edit: not really. you need to be able to see the output and see if it's a nice triangular shaped wave from about -2 to +2 V IIRC (may be +/- 1.5). It's very rare that the VSS goes bad, but it does happen. you can test it by hooking a digital speedo to the VSS circuit or a tripminder and see if they meter out mileage correctly, but short of having any of that on hand, you can't really test them with a basic multimeter. The better test may be to just make sure the wires aren't shorted to each other in the harness. Ringing out the wires and making sure they aren't cut/damaged would be the best bet without other test equipment. Too bad you're not near me, I could test that in about 10 minutes.

[tjc78]

Did they use the backup vacuum deactivate switch in 84? That could be causing the trouble as well.

[gadget73]

They do. Thats the first place I'd check, just because its by far the easiest thing to fool with. Under the dashboard, above the brake pedal you'll find a button that needs to be fully depressed when the pedal is up. If its not, the cruise won't work. You can function check it with a vacuum pump. Under the hood at the cruise servo there is a line from one side of the cruise ball to the other with a tee in it. Pull the line that goes down into the dashboard and pull vacuum. If it doesn't at least mostly hold, the dump valve is bad or out of position. fix that and test it again.



An analog voltmeter may test the VSS, but a tripminder is probably more reliable. Most people don't happen to have scopes that will run on 12v.

[sly]

yeah... that little electronic kit scope I have comes in epiccally handy for automotive stuffs.

This is the one I have. works great. I modified mine and put a BNC jack on it in place of the RCA jack, but they make BNC-RCA adapters too. I already had a bunch of BNC type leads from school... so that my reasoning.

http://www.robotshop.com/en/jye-tech-1mhz-single-channel-digital-oscilloscope-kit.html?utm_source=google&utm_medium=base&utm_campaign=GoogleUSA

[ReneGoFast]

Vacuum Sucks! Now I Have Cruise control.

[QUOTE=gadget73;726657]They do. Thats the first place I'd check, just because its by far the easiest thing to fool with. Under the dashboard, above the brake pedal you'll find a button that needs to be fully depressed when the pedal is up. If its not, the cruise won't work. You can function check it with a vacuum pump. Under the hood at the cruise servo there is a line from one side of the cruise ball to the other with a tee in it. Pull the line that goes down into the dashboard and pull vacuum. If it doesn't at least mostly hold, the dump valve is bad or out of position. fix that and test it again.


Whoohoo! Gadget73 you are a genius....I have been driving my 89 grand Marquis for years with out cruise, unable to find any troubleshooting guides not knowing what to look for, and in 5 minutes under the dash I now have Cruise Control. So simple yet so confusing not knowing where to start or what to look for..I reached up and pushed the plastic plunger back into a hole that looked likea cigarette lighter until the plunger was depressed, an presto it works! Now, what is suppose to keep the plunger/ actuator from popping out of that hole.?

[drhill]

For whatever it's worth, my problem turned out to be a shorted vss wire under the car...everything is a ok now...already done 1000 miles on our trip many of which were on cruise!

[jaywish]

Allright glad to hear it.

[gadget73]

Now, what is suppose to keep the plunger/ actuator from popping out of that hole.?

Cool, glad you found it. THe plunger is supposed to have little plastic ribs that keep it from falling out, but they wear out over time. Usually it holds OK unless someone has been under the dash and bumps it though.


drhill, nice fix on the VSS wiring. Wiring faults can be a pain to chase out.

[klwinter2]

cruise control troubleshooting

Still no cruise..
Test completed:
Brake lights fixed and working
Steering column dump valve tested and working
varied voltage output correct from each cruise function button.
Vacuum present at actuator.
Throttle actuator cable functioning
Actuator disassembled and inspected.. I applied vacumn but could not figure out which internal solinoid to charge to see the cable move... Any insight.
12 Power to the buttons and control unit...

What else...??

I would like to be able to know what wire to bypass to get the actuator to pull the cable...
Car ignition on..
Remote vacumn source to actuator
Apply voltage to ( ------ wire) to make the cable move...

Please make suggestions...

[klwinter2]

THe VSS is the only input that I can not test for the proper input

How did you discover the VSS fault.?
I have examined the sensor and wires. There is not obvious damage..

Kenneth

[91merc]

They do. Thats the first place I'd check, just because its by far the easiest thing to fool with. Under the dashboard, above the brake pedal you'll find a button that needs to be fully depressed when the pedal is up. If its not, the cruise won't work. You can function check it with a vacuum pump. Under the hood at the cruise servo there is a line from one side of the cruise ball to the other with a tee in it. Pull the line that goes down into the dashboard and pull vacuum. If it doesn't at least mostly hold, the dump valve is bad or out of position. fix that and test it again.



An analog voltmeter may test the VSS, but a tripminder is probably more reliable. Most people don't happen to have scopes that will run on 12v.

on mine the little plastic tab on the side of the brake pedal that catches said button is broken