All 4.3L engines are equipped with a MAP sensor, and use the speed density method to compute the airflow rate. Control module uses manifold pressure to calculate the airflow rate. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes. The control module sends a voltage signal to the MAP sensor. Manifold pressure changes result in resistance changes in the MAP sensor.
By monitoring MAP sensor signal voltage, the control module determines manifold pressure. If MAP sensor fails, the control module supplies a fixed MAP value, and uses the TP sensor to control fuel.
Some models also use a Intake Air Temperature (IAT) sensor. Sensor allows control module to determine intake air temperature. Control module uses signal to delay EGR until intake air temperature reaches about 40°F (5°C). If intake air temperature becomes excessively high, control module compensates by slightly retarding timing.