Manifold Pressure/Vacuum Sensor: Testing and Inspection

1984 Chevrolet Corvette V8-350 5.7LSECTION Testing and Inspection

Fig. 022 - Wiring Diagram for MAP Output Check. VIN 8:





CHART C-2D, MAP OUTPUT CHECK

The Manifold Absolute Pressure sensor (MAP) measures manifold pressure (vacuum) and sends that signal to the ECM. The ECM uses this information for fuel and spark control.


Fig. 021 Chart C-2D - MAP Output Check:





1. Checks MAP sensor output voltage to the ECM. This voltage, without engine running, represents a barometer reading to the ECM.
2. Applying 34 kPa (10 inches) vacuum to the MAP sensor should cause the voltage to be 1.2 volts less than the voltage at Step 1. Upon applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. Check vacuum hose to sensor for leaking or restrictions. Be sure no other vacuum devices are connected to the MAP hose.



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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.