My cruise control stopped working. I have checked the clutch and brake switches and I have good vacuum. My speedometer works so I have ruled out the VSS. That leaves the Cruise Control Servo in the engine bay and the Cruise Control Module in the dash. The Cruise Control Servo is next up on the testing. So, does anyone know what the pins are on the Cruise Control Servo so I can bench test it by activating the vacuum solenoids inside it to see if the diaphragm moves? Any other ideas on this?

 

Be sure to start with the fuse, and check your power and ground (switch function).

 

Give me a day to send u the Factory Service Manual diagrams.

 

Fuse, power and ground all good. Thanks in advance for the service manual diagrams. The only one I could find didn't give any info on the pins for the actuator to be able to bench test it.

 

So, I decided to take my Cruise Control Servo apart to see how it works. Here is what I found. There are three solenoids to operate the servo mechanism. The first solenoid is the Vacuum Valve that allows vacuum to pull air out of the diaphragm and allow the diaphragm to pull on the throttle cable. The second solenoid is the Vacuum Release Valve that rapidly lets air into the diaphragm to release pull on the throttle cable. I cleaned mine and reassembled it. I then tested the two solenoids to verify they "clicked" in and out with 12 volts (using a current limited power supply) applied and released. They both worked. I then hooked the vacuum and release lines from the car to the servo connector pins (connector disconnected) with it running and connected the 12 volts to both solenoids at the same time. This should be normal operation so that the vacuum was applied and the release valve was closed. The diaphragm pulled all the way in. After removing 12 volts to the vacuum valve solenoid, the diaphragm held in the pulled-in position. I then removed the 12 volts to the release valve solenoid and the diaphragm released as air was let in.

Now to the third solenoid. It appears to be the computer control solenoid that varies how far in the diaphragm can pull the throttle cable. On my bench test I didn't get any movement applying or removing 12 volts across the solenoid terminals that I could tell from the solenoid relative to the diaphragm. I assume that it is designed to push out and prevent the diaphragm from pulling in further than the computer will allow. That is pull in more when the car drops below the desired speed and push out when the car exceeds the desired speed. Anyway, I am thinking my servo may be bad but I am not sure I got a valid test on the third solenoid.

Here is the pinout I created for my 92 servo:

Looking at the back of the servo (opposite end from the diaphragm) and with the connector pins down at the 6 o'clock position, I arbitrarily labeled them 1 through 5 with 1 being on the left end of the pins.

Pin 1 -- Vacuum Control Valve Signal (A) (Likely pulled to ground by the computer when Set)
Pin 2 -- Control Solenoid Signal 1
Pin 3 -- Common Connected to one side of the Vacuum Control Valve (B) and one side of the Vacuum Release Valve (D) (Probably 12 volts when Cruise is turned on so the computer can ground the signal lines)
Pin 4 -- Control Solenoid Signal 2
Pin 5 -- Vacuum Release Valve Signal C (Likely pulled to ground by the computer when Set)

Note: The Vacuum Control Valve opens when activated and the Vacuum Release Valve closes when activated.

I will need the wiring diagram to see how Pins 2 and 4 are connected to the computer to get a better idea how it is supposed to operate.