Cruise Control: Testing and Inspection
Fault tracing, cruise controlAlways start with the following checks in case of cruise control malfunction.
Experience shows that one of the following items most likely is at fault.
Fuses
Fuse No. 1 in the fuse box and in-wire fuse at the pedal assembly.
Vacuum valve at the brake pedal
No vacuum leak permitted. To check:
- Disconnect the big vacuum hose at the throttle actuator. Blow into the hose. It should be airtight.
In case of a leak, check that the vacuum valve is correctly adjusted. It should be fully closed with the brake pedal released. Also check valve and hose for leaks.
Vacuum hose to intake manifold
It should be free from obstructions and not leaking. To check:
- Disconnect the thin vacuum hose at the throttle actuator. Start the engine and use a finger to block the end of the hose and feel vacuum force. Release to check that the idle speed increases and becomes erratic.
Retard switch position
It should be set at a 170 angle to horizontal (see diagram). The retard switch is a mercury switch and it is important that the angle is accurate. Otherwise the flow of current will be interrupted.
Brake light
The governor is grounded through the brake light bulbs. If both bulbs are defective, the governor will not operate.
Brake light wires
Should be correctly connected. Check wiring diagram.
Brake light switch adjustment
The brake lights should come on before the brakes are actually applied.
Clutch switch (manual transmission)
Should be correctly connected (see diagram) and adjusted.
Cars equipped with indicator light should be wired as follows:
The red wire 1 should be connected with the fuse to the positive side of the brake lamp contact.
The brown wire 2 should be connected to the clutch contact with a splice-connector 3.
The red wire 4 should be connected between the clutch contact and the negative side of the brake lamp contact.
The black wire 5 should be disconnected from the clutch contact.
The switch pin should be completely pressed in when the clutch pedal is disengaged.
Wires and connectors
Should be correctly and firmly connected.
Throttle actuator ground wire
Green wire, check for correct ground.
Throttle control bobbin
Mounting screws must be tight and secured with suitable thread-locking compound.
Road speed pickup coil
Check for properly attached wires.
NOTE: The tape around the pickup coil may interfere with proper cruise operation.
If no fault is found, continue with checks A-E, as follows.
A. Check wiring
Use a small drill bit or equivalent to depress TERMINAL RELEASE. Pull out the connector.
Use a test light for these checks.
B. Check cruise control switch
B1. Disconnect the connector at the cruise control switch
B2. Connect a jumper wire from 1 2V current source (for instance the fuse box) to red wire terminal in connector.
B3. Connect a test light across ground and the three wires, in order.
B4. Correct test light indication is shown in table at left. Replace the cruise control switch in case of incorrect indication.
C. Check road speed pickup coil
The speedometer contains rotating magnets which induce a varying AC voltage in the pickup coil. This signal is used to indicate road speed to the governor
Check for AC voltage as follows.
C1. Disconnect the 14 pin plug at the governor.
C2. Connect an AC volt meter (2.5V scale approximately) with a 1K Ohm resistor parallel across the leads to terminals 2 and 3 as shown.
C3. Raise rear wheels off floor and run car in gear at indicated 30 mph.
C4. The voltage signal should show an AC voltage.
The regulator uses a minimum of 0.5 volts at 30 mph (48KPH). You will see an increase in voltage as speed increases.
The pick-up is OK if a voltage is present. If no voltage is indicated, check the continuity of the wires and pick-up coil. The coil's resistance is approximately 500-750 ohms.
D. Check resistance of throttle actuator
D1. Switch ignition OFF.
D2. Depress TERMINAL RELEASE (arrow) and disconnect the connector
D3. Check resistance; see table. Use ohmmeter with high degree of accuracy better than ±2%.
D4. In case of incorrect resistance, first check wiring before replacing components.
D5. If readings are correct, continue with check E
E. Check vacuum motor
E1. Switch ignition OFF.
E2. Disconnect the two connectors for the throttle actuator.
E3. Disconnect the big vacuum hose at the throttle actuator.
E4. Disconnect the throttle cable at the pulley.
E5.
a. Connect ohmmeter NEG to one of the throttle actuator stud bolts.
b. Connect ohmmeter POS, in order, to maroon, orange, and white wires in connector.
c. The ohmmeter should indicate infinity.
In case of resistance readings between 0 to infinity there is a short in the throttle actuator. It should be replaced.
A short in the throttle actuator damages the transistors in the governor, this requires that the governor also be replaced.
In case of no ohmmeter readings, continue on tests 6-8.
E6. Connect a vacuum gauge to the large vacuum hose connection at the throttle actuator.
E7. Apply the parking brake. Gear selector in Park or Neutral. Start the engine.
E8. Connect a jumper wire across ground and orange wire in connector. Connect a second jumper wire from a 12V current source to white and maroon wires simultaneously. The vacuum meter should indicate vacuum. Disconnect the 12V source jumper wire. No vacuum should be present.
Repeat Step 8 several times to make sure the throttle actuator valves operate correctly.
If the throttle actuator operates correctly, replace the governor.
F. Replacing the governor
The governor cannot be easily tested without installing it in a known good cruise system.
NOTE: Perform ALL other tests before checking or replacing the governor.
G. Adjusting governor
NOTE: Use care in performing these adjustments as the potentiometers are the delicate wafer type.
The governor has three adjusting screws. The adjustments are set at the factory for the average vehicle. The adjustment can be set to the factory setting by the following steps.
If the factory adjustments are not suited to the driver of the vehicle, use the following steps to fine-tune the governor.
Remove the governor without disconnecting harness. During the test drive, make adjustments in the order listed below.
CAUTION: Make adjustments while vehicle is stationary.
Low speed switch adjustment
The system should not engage below 30 mph. Hold the cruise control switch in RESUME position. From a low speed, accelerate slowly using the throttle pedal. Note the speed at which the cruise control system engages (the throttle pedal will be pulled down by the throttle actuator).
Turning the screw clockwise increases engagement speed, counterclockwise decreases it.
Centering adjustment
The system should hold the set speed within ±3 mph limits.
Drive on level road with a speed of approximately 45 mph. Switch to ON position and depress SET SPEED. Let the cruise control take over.
Turning the screw clockwise maintains closer control limit, counterclockwise widens control limit.
Sensitivity adjustment
The governor is adjusted at the factory for maximum sensitivity. The cruise control system continuously adjusts the throttle control according to any differences in road and driving conditions.
Sensitivity can be reduced for vehicles driven mostly with light cargo load or to improve fuel mileage. This will also influence the centering adjustment (governor adjustment B) to a certain degree.
If all input signals are correct and the governor cannot be adjusted to function properly, replace it.