Air Charge Temperature Sensor

by Bob O’Neill and Bob Lincoln

The signals from the Air Charge Temperature sensor and the MAP sensor are used to monitor both the temperature and pressure of the air entering the combustion chamber.  This information is used by the ECU to calculate fuel delivery.  This is especially important at WOT or wide open throttle. 

In the 1984 model year, the sensor was a thermistor (temperature-sensitive resistor) used with a fixed resistor; together they measure between 5,290 ohms to 5,610 ohms at 77° F.  Using the resistor with the thermistor increases the accuracy of the sensor at higher temperatures.

The sensor design for 1985 and later years used just the thermistor, which measures between 9,120 ohms to 10,880 ohms at 77° F. In both cases the voltage from the sensor should be around 2.5v at 77° F.

The sensor was not used in 1988 model year Turbo I engines; the ECU used results from the battery temperature and coolant temperature sensors to calculate the incoming air temperature. Still, for Turbo 2 engines, the sensor was used, because the temperature of the air charge could vary based on how efficiently the intercooler cooled the air charge.

The sensor was discontinued after 1991 for TBI engines.

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