DESCRIPTION
System uses manifold vacuum to power a throttle servo unit. When speed adjustment is necessary, the servo moves the throttle by receiving a varying amount of controlled vacuum from a transducer.
The speedometer cable from transmission drives the transducer. A cable from the transducer drives instrument panel speedometer. There are 2 control switches operating speed control. The first is a "CRUISE" slide switch with "OFF", "ON" and "RESUME" positions.
The second is a "SET-COAST" button switch located on the end of turn signal lever. It controls engagement of transducer. Two brake release switches are provided.
An electric switch disengages transducer. A vacuum valve (switch) decreases vacuum in the servo unit to quickly return throttle to idle position when the brake pedal or clutch is depressed.
OPERATION
This system is designed to operate at speeds above 25 MPH. "CRUISE" switch must be in "ON" position to activate speed control system. Driver accelerates to desired speed, then partially depresses and slowly releases speed control "SET-COAST" switch button.
To change speed setting to higher speed, depress accelerator until desired speed is reached, then fully depress and slowly release "SET-COAST" switch.
To change speed setting to lower speed, depress "SET-COAST" switch fully. Hold in this position until vehicle has decelerated to new desired speed setting. Then, release "SET-COAST" switch slowly to re-engage speed control.
Speed control system is disengaged by applying brakes. To accelerate vehicle to previously set speed in memory, slide "CRUISE" switch to "RESUME" position.
Accelerator pedal may be depressed at any time to override speed control system. Release of accelerator returns speed to previous level. Sliding "SET-COAST" switch to "OFF" position or turning ignition "OFF" will also disengage the system and erase the "RESUME" memory.
PRELIMINARY INSPECTION
- First make a visual inspection. Check the system to make sure there are no bare, broken or disconnected wires, or pinched, damaged or disconnected vacuum hoses.
- The servo and throttle linkage should operate freely and smoothly. Servo linkage should be properly adjusted. If the visual inspection does not reveal any problems, further testing is required.
CRUISE SYSTEM INOPERATIVE
Disconnect brake and clutch switch. Check continuity with pedals in "free" position. If continuity shows an open, adjust or replace the brake/clutch switch as necessary. Check the vacuum release valve and the combination vacuum release valve/converter clutch switch for vacuum operation. If leaking, replace. If misadjusted, adjust.
SERVO CHECK
- Disconnect the electrical connector at the servo. Make sure the connector and pins are free of corrosion. Check resistances. Resistances should be as follows. If not, replace servo unit. SERVO PIN RESISTANCES Pin Number Ohms A-C 10 E-C 10 B-D 5
- Turn off ignition switch then disconnect the body harness connector from the Vehicle Speed Sensor buffer amplifier. Connect a Speedometer Signal Generator (J-33431) to amplifier connector. Disconnect the servo throttle linkage at the servo unit. Set the signal generator to 54 MPH and 30 Hertz square wave position. Start the engine and move mode switch slider to "ON" position.
- Depress and release "SET/COAST" switch. Servo should pull to approximately 28-42% of servo position travel and hold. Move cruise lever and slider to "RESUME ACCEL" position and hold for 3 seconds. Servo will pull to the full stroke position and hold.
- After releasing slider from the "RESUME ACCEL" position, the servo will return to 28-42% of the travel position. Momentarily move the CRUISE lever slider to "RESUME ACCEL" position. Servo will pull to the 28-42% position of travel and hold.
- If tests in steps 3) and 4) do not perform as indicated, check the harness for defects, then make electrical and pneumatic tests as needed. If steps 3) and 4) do perform as indicated, a buffer amplifier or pulse modulator generator defect is indicated.
ELECTRICAL CHECK
Check fuse. Check chassis ground and harness. Perform continuity checks with ohmmeter between controller and servo. Check the Mode Control Switches by replacing with a known good switch or test for continuity as listed in Mode Control Switch Continuity table.
| Set/Coast Switch | O = Open, C = Closed | |
|---|---|---|
| Normal | ||
| Position Slider | Off | |
| 1-2 | O | |
| 1-3 | O | |
| 1-4 | O | |
| 2-3 | O | |
| 2-4 | O | |
| 3-4 | O | |
| Normal | ||
| Position Slider | Off | |
| 1-2 | O | |
| 1-3 | O | |
| 1-4 | O | |
| 2-3 | O | |
| 2-4 | O | |
| 3-4 | O | |
| Normal | ||
| Position Slider | R/A | |
| 1-2 | O | |
| 1-3 | O | |
| 1-4 | C | |
| 2-3 | O | |
| 2-4 | C | |
| 3-4 | O | |
| Depressed | ||
| Position Slider | Off | |
| 1-2 | O | |
| 1-3 | O | |
| 1-4 | O | |
| 2-3 | C | |
| 2-4 | O | |
| 3-4 | O | |
| Depressed | ||
| Position Slider | Off | |
| 1-2 | O | |
| 1-3 | O | |
| 1-4 | O | |
| 2-3 | C | |
| 2-4 | C | |
| 3-4 | C | |
| Depressed | ||
| Position Slider | R/A | |
| 1-2 | C | |
| 1-3 | C | |
| 1-4 | C | |
| 2-3 | C | |
| 2-4 | C | |
| 3-4 | C | |
MODE CONTROL SWITCH CONTINUITY
Mode Control Switch Wire Identification. Scheme 1
PNEUMATIC CHECK
- Disconnect bead chain or rod and electrical connector at the servo unit. Start the engine. Apply 12 volts between A and C. Apply 12 volts between E and C. Servo should move full stroke. If not, check the vacuum hoses to the vacuum supply. Remove voltage from E and C.
- The servo should move a full stroke. If not, disconnect vacuum brake release at the servo and plug the servo. Momentarily apply 12 volts between E and C to allow the servo to full stroke. If the servo holds its position, adjust the brake vacuum release valve or replace the valve. If no defect is found in any of the tests, replace the electronic controller.
Servo Terminal Lettering. Scheme 2
1.9L 4-Cylinder & 2.8L V6 Engines
- With cable assembly installed to cable support and carburetor, install cable assembly to servo bracket, using second ball only on servo chain on cable.
- With throttle completely closed (ignition off and fast idle cam off) adjust cable jam nuts until there is a .040" (1.0 mm) clearance between throttle lever stud and end of cable slot. Tighten jam nuts.
2.0L 4-Cylinder Engine
- With cable assembly installed to cable support and carburetor, install cable assembly to servo bracket, using second ball only on servo chain on cable.
- With throttle completely closed (ignition off and fast idle cam off) adjust cable jam nuts until cable sleeve at carburetor is tight but not holding throttle open. Tighten jam nuts.
4.0L 6-Cylinder Engine
Using third ball only on servo chain, and with throttle completely closed (ignition off and fast idle cam off) adjust cable jam nuts until there is a .040" (1.0 mm) clearance between stud pin and end of slot. Tighten jam nuts.
4.8L 6-Cylinder Engine
With cable assembly installed and using second ball only on servo chain, install servo assembly chain on cable assembly. With throttle completely closed, (ignition and fast idle cam off), adjust cable assembly jam nuts until there is .040" (1.0 mm) clearance between lever pin and end of cable assembly slot. Tighten cable assembly jam nuts.
All Gasoline V8 Engines
With ignition off and fast idle cam off (throttle completely closed), adjust length so that rod assembles over end of stud. Install retainer.
6.2L V8 Diesel Engine
With engine not running and idle screw against stop, assemble lower end of rod link to throttle lever and upper end to hole closest to servo which will provide a minimum of .040" (1.0 mm) slack.
