'93 Buick Regal Cruise Control

Darrenp

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#1
Hey all:
'93 Buick Regal Custom, 3. 8L, 59700 Miles, 3 sp. auto with overdrive and torque lock, all OEM.

I was 1 hr. into a 5 hr. trip over the weekend doing 70 on the cruise control on the Interstate. Everything was fine and the cruise control just turned off, like I had tapped the brake. I tried the set button and the resume button, but the cruise light comes on for about a second and goes back off. The cruise control does not set now.

Should I be looking at the "talkback line" (vacuum hose from the cruise control module that goes through the firewall and to the vacuum break switch on the brake pedal)? It looks a little deteriorated under the hood (at 15 years in that heat, there is no wonder), but is in very good shape under the dash. I pulled the dash cover off and inspected the line and switch under the dash for cuts or mis-adjustment. Fishing a new line through the firewall and to the switch looks like a real pain in the you-know-what.

Or, is there another fuse or breaker for the cruise control someplace other than the three fuse blocks on the car (2 under the hood and one in the glovebox)? I checked every fuse on the car as I do not have the manual. All are good. Any other ideas or concerns on this system?

The car is pristine except for a dent in one door. I do a few trips, and with family being out of state, the smallest trip is 5 hours. Gives me a cramp in my right leg, so I would like to get the cruise working again.

Thanks in advance.

Darren
 

Darrenp

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#2
UPDATE:

Well, the hose from the cruise control to the brake pedal both holds a vacuum and pressure. The diaphram on the outside of the unit where the linkage to the throttle attaches is also in one piece with no holes or tears. Pulled the vacuum line off with the engine running and there is plenty of vacuum at the line.

Is there an electical switch on the brake pedal for this system? The brake switch has two electrical plugs on it. The brake lights work fine. Is the other one for the cruise control or the shift lockout?

Any ideas?

Darren
 

Darrenp

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#3
Hmmmm

Well, this is a first. Nobody has any input. . . . ;D

I will need to contact my local salvage yard and see if they have one of the servo units as I am out of ideas. I can't afford a new one.

Darren
 
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#4
I did completely take apart the servo in my 82 Chevy, the kind with the speedometer cable going in and out with the solenoid locked governor. Had to decrimp and crimp the diaphragm container and just prayed the diaphragm was good and it was, but sure was rusty on the inside, cleaned all that up relubricated an painted and it works like a charm now. Besides the control and brakes switches, this unit is self contained.

Yours is different, just about everything plugs into the PCM, servo has two vacuum switches in it, the vacuum motor, and an AC servo for PCM feedback that all plug into the PCM for control. As does the control switches and the two brake switches, they both have to have closed contacts with zero ohms for the thing to work, plus a good vacuum switch. Your speed control comes from the Vss that hit's the PCM with pulses, but your speedometer and AT shift points also work off that thing.

While I fully rebuilt my 82 without a manual, made my own circuit diagram, wouldn't want to fool with the 93 version without a manual, stuff running all over the place. And typical of GM can well be just one corroded connector, I got in the habit of cleaning all of them, but great care must be used with the PCM, it's easy to fry it.

Drove for over twenty years without cruise, but now can't live without it, too darn easy to get a speeding ticket. You could try alldata.com for the circuit. BTW, the new ones are all electronic, no vacuum to screw around with.
 

Gus

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#5
Saw your post, unfortunately I forgot to look it up at work.....You should have vacuum on the small line to the unit and vaccumm in the line to vac switch at the brake....yes, you should also have an electrical switch at the brake pedal.....you really need a schematic to test the harness at the unit to check for power and ground and signals from the cruise switch and brake switch....if all are ok, then I would suspect the unit....
 

Darrenp

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#6
Thanks.

All connectors are clean and non-corroded. Vacuum is ok, and the vacuum switch at the brake pedal is good by testing with a vacuum applied to the line and depressing the brake. I believe the electrical switch on the brake works because if I try pressing the set switch at speed, I get the cruise light to come on for about a second. If I lightly touch the brake while hitting the set switch, there is no cruise light at all, which is what I would expect.

Since the speedometer and every thing else is completly fine, I think that I am down to the servo unit. I will have to contact my local salvage yard, as with my wife loosing her job, I cannot afford a new one.

Thanks again.

Darren
 
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#7
Something is missing with that flash of light, with my old 82 cruise control, could see it work with my eyes, a governor operated switch had to be closed, the speed lock solenoid was pulsed by the directional level cruise control switch causing that solenoid to energize closing a set of holding contacts to keep that solenoid energized where shutting down the cruise switch or stepping on the brake pedal would de-energize that solenoid by breaking the 12 volt supply.

I did look at your servo at rockauto.com, nothing like the one in my DeVille, but the one in my DeVille was very easy to test with just two solenoid activated vacuum switches in it. Energize one would open the vacuum to the diaphragm where applying vacuum would move the throttle cable, the second solenoid dumped the vacuum in a flash, AC servo was just a coil of wire that I made a continuity check on.

In these newer systems, the PCM does the brain work, looks for that closed contact to start it up, a closed brake switch, Vss signal of the proper speed, around 25 mph equivalent, not sure about the MAP sensor, but apparently yours is getting the pulse from the start switch, but missing something else to keep that solenoid engaged. With a circuit and hand vacuum pump, should be able to test the servo, and make sure the other signals are reaching the PCM. Perhaps someone will post the circuit for you, I lost my access to a host of circuit diagrams when I retired.

Ha, like that old stuff better, can see what's going on, but this new stuff is much cheaper to make, only cost pennies, but you don't get a new one for pennies, more like a second mortgage on your home.
 

Darrenp

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#8
OK. I think that I found out that there is a cruise control servo and a module. The servo is plainly visable under the hood. However, does anyone know where the module is located? ???

I know what it looks like, but I do not know where it is. Is it by the ECM? I don't remember seeing it when I had the splash shields off when I was replacing the radiator hoses. The computer was plainly visible, but I was not looking that hard. If it is there, it is possible that I knocked the wires loose putting the splash shields back after replacing the hoses. Or, please don't say it, is it buried in the dash? If it is in the dash, it will be a royal pain to get to I know. But I want to look at everything and not throw parts at it.

If somebody knows, please let me know. Thanks.

Darren
 
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#9
I can't work on this stuff with some kind of a manual, cheapest would be an alldata.com subscription. Typically after the late 80's stuff like a separate AT or cruise control module is part of the engine control computer or the PCM. That makes more money for the manufacturers, but not quite so easy to troubleshoot as you are dealing with a massive cable full of wires where you can't tell one from the other without a manual.