Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Speed Density (Except 3.8L)
All gasoline vehicles except 3.8L are equipped with a MAP sensor, and use the speed density method to compute the airflow rate. ECM uses manifold pressure to calculate the airflow rate. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes. The ECM 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 ECM determines manifold pressure. If MAP sensor fails, the ECM supplies a fixed MAP value, and uses the TPS to control fuel.
2.5L and 4.3L turbo models also use a Manifold Air Temperature (MAT) sensor. Sensor allows ECM to determine intake air temperature. ECM uses signal to delay EGR until intake air temperature reaches about 40°F (5°C). If intake air temperature becomes excessively high, ECM compensates by slightly retarding timing.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.