Question about 1995 Geo Prizm
A MAP sensor problem will cause the symptoms you are experiencing. The MAP sensor is critical because you have a speed density type fuel injection
system. Without the MAP sensor signal or an inaccurate one, the ECM won't know the engine load for ignition timing and fuel injection adjustments. The engine computer is detecting a high voltage condition on the MAP sensor signal circuit.
Inspect the vacuum hose going to the MAP sensor. Replace it if is looks cracked or if it collapses on itself. Make sure that the MAP sensor has vacuum by disconnecting the hose from the sensor when the engine is running and feeling for vacuum.
If you have vacuum, you can check the MAP sensor and its circuits with a multimeter. There are three wires going to the sensor. I am not sure on the colors, but Yellow should have 5 V on it with the key on. Brown is ground and should read close to 0 ohms. Light Green with a Red stripe should have 5V on it with the key on. If you backprobe the MAP sensor connector with it plugged into the MAP sensor on the light green/red wire and apply vacuum to the sensor, the voltage should drop.
Posted on Jul 20, 2009
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Posted on Jan 02, 2017
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