- Bypass the control module by connecting the carburetor vacuum port and the single vacuum hose (upstream of temperature-sensing vacuum control valve) to the distributor, together, at the rear of the engine.
- Check the distributor vacuum advance operation. If it is correct, the difficulty is probably in the modulator system.
- Return all connections to normal. Pull the hose from the carburetor vacuum port and connect a vacuum gauge in its place. Note the vacuum reading at 1,500 rpm. Remove the gauge and replace the hose.
- Bypass the control module as in step one. Connect the vacuum gauge to the primary (outside) distributor vacuum connection. Note the vacuum reading at 1,500 rpm.
- Remove the control module bypass hose. Reconnect the module hoses. If the vacuum reading is zero or less than that in step three, check for blockage or leaks in the vacuum system. If the vacuum readings are about equal, proceed with step six.
- Leave the vacuum gauge connected as in step four. With the engine idling at normal operating temperature, raise the rear wheels. Disconnect the thermal switch from the pillar post. Hold it in your hand long enough to warm it above 68°F.
- Shift into Drive and slowly accelerate to 35 mph. Note the vacuum reading. If the gauge reads zero at all speeds, check the electrical connections, hose connections, and control module. If the vacuum cuts in between 20-30 mph, the system is operating correctly. If the vacuum cuts in at start of acceleration or before 20 mph, check the electrical connections, hose connections, control module, and speed sensor.
- Unplug the sensor. Using an ohmmeter, attach one lead to each speed sensor wire connection. The reading should be 40-60 ohms at room temperature.
- Attach one ohmmeter lead to the black wire on the speed sensor and the other to the sensor housing. The ohmmeter should read zero.
- If the readings are not correct, replace the sensor. It is not repairable.
See Figure 1
- Unplug the switch. Connect one ohmmeter lead to the gray (or white) wire and the other to the black.
- Warm the switch in your hand. The ohmmeter should read zero with the switch at 58-68°F or higher.
- Chill the switch with cold water. There should be an ohmmeter reading at 58-50°F or lower.
- Replace the switch if the readings are not correct. It is not repairable.
- Unplug the connector for red and gray wires from the module. Reconnect the red wires with a jumper wire.
- Connect a vacuum gauge to the carburetor vacuum port. Run the engine at fast idle and note the vacuum reading. Reconnect the vacuum hose.
- Connect the vacuum gauge to the primary (outside) distributor vacuum connection.
- Ground the gray (or white) wire from the control module.
- Run the engine at fast idle and note the vacuum reading.
- Replace the control module if the vacuum reading in step five is not the same or slightly less than that taken in step two. The module is not repairable.