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.
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HOMESERVICE MANUALSCHEVROLET1990R 20 P/U 2WD V8-350 5.7LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONSCAN TOOL TESTING AND PROCEDURESPOSITIONSMAP - MANIFOLD ABSOLUTE PRESSURE
1990 Chevrolet R 20 P/U 2WD V8-350 5.7L
MAP - Manifold Absolute Pressure
1990 Chevrolet R 20 P/U 2WD V8-350 5.7LSECTION MAP - Manifold Absolute Pressure
Indicates voltage signal from MAP sensor. Voltage readings are low when manifold pressure is low (high vacuum), and signals increase as manifold vacuum decreases. With ignition off and engine stopped, manifold pressure is equal to atmospheric pressure and voltage signals will be high (nearly 5 volts). With engine running, normal readings are 1-2 volts.
Comparison of sensor readings with readings from known good sensor can be used to isolate malfunctioning sensor. Sensors have a color code tab in the connector cavity, and sensors with the same colored tab have identical calibration. Readings from sensors with like identification tabs should be the same to within ±.4 volt.
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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.