Tech Tips
Temperature Sensor
Is your fuel injected Z (1995 and up) consuming a lot of gas, fouling spark plugs, stumbling on acceleration, or hard to start?
The fault may be with your temperature sensor.
The coolant temperature sensor (75-79) or cylinder head temperature sensor (80 and up) plays an important role in the performance of your Z car. The sensor “tells” the engine management computer the temperature of the coolant or cylinder head so that it, the computer, can adjust the injector pulse width (the length of time the injectors stay open and therefore the amount of gas that can enter the combustion chamber). The sensor talks to the computer by way of varying resistance (ohms). When the temperature is low the resistance of the sensor is high and vice versa.
How can we accurately diagnose a bad sensor? First we need a couple of tools. The most important tool is a factory service manual. The factory manual not only shows the location of the sensor but it also contains a graph and chart that clearly indicates the relationship between temperature and resistance. We will also need an ohm meter. With the engine stone cold, disconnect the sensor from the harness. Using your ohm meter, measure and record the sensor resistance. Start the engine and allow it to reach approximately 120 degrees as indicated by the coolant temperature gauge. Stop the engine, measure and record the sensor resistance. This step is important because the sensor must be accurate not only at the temperature extremes but also throughout it’s range. Restart the engine and allow it to reach normal operating temperature or about 180 degrees. Stop the engine, measure and record the sensor resistance. If any of your findings vary significantly from the factory specifications, you have a defective sensor.
It’s important to note that if your car has a defective thermostat, stuck fan clutch or anything else that prevents the engine from reaching normal operating temperature, it CANNOT operate at maximum efficiency.
A word of caution, some models employ a short wiring harness between the sensor and the main injection harness. If you find that the sensor is OK, you may have a bad sensor harness. It too can be checked with your ohm meter. It should measure 0 ohms. Frequently the connectors at either end can, over time, become corroded effectively blocking the resistance signal from reaching the computer. As a practical matter whenever I find a bad temperature sensor and a sensor harness that’s old and therefore suspect, I replace both simultaneously. It just makes good sense.
Good hunting!
Mike McGinnis
Banzai Motorworks
The fault may be with your temperature sensor.
The coolant temperature sensor (75-79) or cylinder head temperature sensor (80 and up) plays an important role in the performance of your Z car. The sensor “tells” the engine management computer the temperature of the coolant or cylinder head so that it, the computer, can adjust the injector pulse width (the length of time the injectors stay open and therefore the amount of gas that can enter the combustion chamber). The sensor talks to the computer by way of varying resistance (ohms). When the temperature is low the resistance of the sensor is high and vice versa.
How can we accurately diagnose a bad sensor? First we need a couple of tools. The most important tool is a factory service manual. The factory manual not only shows the location of the sensor but it also contains a graph and chart that clearly indicates the relationship between temperature and resistance. We will also need an ohm meter. With the engine stone cold, disconnect the sensor from the harness. Using your ohm meter, measure and record the sensor resistance. Start the engine and allow it to reach approximately 120 degrees as indicated by the coolant temperature gauge. Stop the engine, measure and record the sensor resistance. This step is important because the sensor must be accurate not only at the temperature extremes but also throughout it’s range. Restart the engine and allow it to reach normal operating temperature or about 180 degrees. Stop the engine, measure and record the sensor resistance. If any of your findings vary significantly from the factory specifications, you have a defective sensor.
It’s important to note that if your car has a defective thermostat, stuck fan clutch or anything else that prevents the engine from reaching normal operating temperature, it CANNOT operate at maximum efficiency.
A word of caution, some models employ a short wiring harness between the sensor and the main injection harness. If you find that the sensor is OK, you may have a bad sensor harness. It too can be checked with your ohm meter. It should measure 0 ohms. Frequently the connectors at either end can, over time, become corroded effectively blocking the resistance signal from reaching the computer. As a practical matter whenever I find a bad temperature sensor and a sensor harness that’s old and therefore suspect, I replace both simultaneously. It just makes good sense.
Good hunting!
Mike McGinnis
Banzai Motorworks
