Are you wondering why even after tune up, your ride still has poor gas mileage? The culprit could be the engine's Manifold Absolute Pressure or MAP sensor. This component converts the manifold pressure to corresponding voltage signal and sends it to the engine computer to inform it about the amount of engine load. The data becomes the basis of the computer for increasing or decreasing the supply of fuel to the engine as well as for adjusting the timing of the spark.
If you're suspecting a bad Manifold Absolute Pressure sensor, you'd better do some troubleshooting to help you gauge whether your sensor needs repair or replacement. Here are the steps in testing your MAP sensor:
Things you'll need:
- Hand vacuum pump
- Voltmeter or tachometer
Locating the sensor
Step 1: Depending on the vehicle model, the Manifold Absolute Pressure sensor can be found under the dash, in the fender wall, firewall, or in the air cleaner. In some vehicles, it is installed in the intake manifold.
Step 2: Once you've found the sensor, determine what type it is. A voltage type MAP sensor can be tested using a voltmeter while a frequency type requires a tachometer. If you aren't sure about the sensor type, you can consult your owner's manual.
Checking the vacuum hose
Step 3: Make sure the vacuum hose that's connected to the sensor is in good condition. Check for loose wires and faulty electrical connector. Also make sure that the hose doesn't have any obstruction.
Measuring the reference voltage
Step 4: Disconnect the electrical connector from the sensor. Turn on the ignition key without starting the engine. Determine the reference voltage by connecting the reference wire with the positive lead of the voltmeter. The negative lead must also touch the ground-black wire found at the other end of the connector. If the reference voltage is around 5 volts, then you've now found the culprit. If it's within the specifications, proceed with the other tests.
Step 5: Reconnect the MAP sensor and turn the ignition key off.
Attaching the voltmeter/tachometer to the signal wire
Step 6: Connect the negative probe of the tachometer or voltmeter to the black ground wire and the positive probe to the signal wire.
Step 7: Plug the sensor's connector and make sure the reference wire constantly generates 5-volt signal. If you aren't sure about the proper wire connections, consult your manual.
Disconnecting the vacuum hose
Step 8: Detach the vacuum hose from the MAP sensor and put a hand vacuum pump in its place. Put the ignition key to the .on. position without staring the engine.
Reading the rpm or voltage
Step 9: Take note of the voltage or RPM. The result should be between 4.5 and 5 volts or between 300 and 320 rpm with zero inches of mercury vacuum.
Step 10: Apply 5 inches of mercury vacuum. The output should be around 3.75 volts, or between 275 and 295 rpm.
Step 11: Apply 20 inches of mercury vacuum. You should now read about 1.1 volts, or between 200 and 215 rpm. Verify your findings to what's specified in your service manual. If the figures you've obtained are pretty much out of specifications, then it's now time to replace your sensor.