Boost Engine Performance with MAF Sensor Insights

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Purpose

The Mass Air Flow (MAF) sensor monitors the volume of air (airflow and air density) entering the engine. The MAF sensor sends a signal (dc voltage, low frequency, or high frequency) to the vehicle's computer which represents the quantity of air entering the engine. The voltage or frequency increases when air flow increases. The computer adjusts air/fuel ratio and ignition timing based on incoming air flow.

Location

The mass air flow sensor is mounted in the engine incoming air duct, ahead of the throttle body.

Operation

The MAF sensor uses an electrically heated wire (hot wire-type) or foil grid (hot film-type) as the sensing element. The sensing element is maintained at a fixed temperature above the ambient (incoming) air temperature. The incoming air mass cools the sensing element, increasing the amount of current necessary to maintain the sensing element "at temperature."

The amount of cooling provided by the incoming air mass varies due to factors such as air temperature, density and relative humidity. As a result, the amount of current necessary to keep the sensing element "at temperature" is directly proportional to the "mass" of air entering the engine.

Hot wire-type MAF sensors generate a voltage signal output. Hot film-type MAF sensors generate a frequency signal output.

Drivability Symptoms

The following symptoms may indicate a damaged or defective MAP sensor, or trouble in a related system:

• Hard starting
  
• Stalling, stumbling or rough idle
  
• Hesitation during acceleration or while driving under load
  
• Air/fuel ratio problems (fuel mixture is excessively "rich" or excessively "lean")
  
• Increased vehicle emissions
  
• Poor engine performance
  

Drivability symptoms due to a bad MAF sensor can be similar to symptoms caused by a bad throttle position sensor. Be sure to investigate both areas before parts replacement.

Testing

The MAF sensor can be checked using either an analog voltmeter (for sensors that produce a voltage output signal) of a frequency meter (for sensors that produce a frequency output). Refer to the vehicle's service manual to determine the output signal type (voltage or frequency) and the correct diagnostic tool.

NOTE: Refer to the vehicle's service manual for connector pin identification and signal specifications.

NOTE: It may be necessary to disconnect the wiring harness from the MAF sensor and jumper the POWER and GROUND pins from the harness to the sensor in order to facilitate access to the SIGNAL pin for testing. Be sure to jumper the pins properly.

• Set the test meter to the appropriate scale for the vehicle under test.
• Connect the black lead of the test meter to the battery negative terminal (ground). Connect the red lead of the test meter to the MAF sensor’s SIGNAL pin.
• Turn the ignition key on. DO NOT start the engine.
  
  Verify MAF sensor SIGNAL voltage is within specification.
  
• Start the engine and let idle.
  
• Momentarily rev the engine and observe the test meter.
  
  Verify the MAF sensor signal output increases as the throttle is opened.
  
• Return the engine to idle.
  
• Lightly tap the MAF sensor and observe the test meter.
  
  Verify the MAF sensor signal output remains steady when the sensor is tapped.
  
• Turn the ignition key off. Disconnect the test meter from the MAF sensor. Reconnect the wiring harness to the MAF sensor.
  

Troubleshooting

Malfunctions in a number of vehicle systems can result in drivability symptoms similar to those resulting from a faulty MAF sensor. Be sure to check the following areas as well:

• Engine compression problems
  
• Vacuum leaks
  
• Low fuel pressure
  
• Ignition system problems
  

The MAF sensing element can become contaminated in the course of normal vehicle operation. A contaminated sensing element can contribute to hard starting, rough idle, hesitation and stalling. If a dirty sensing element if suspected, use a good quality electronics cleaner to remove contamination. Cleaning the sensing element can often restore normal sensor operation.

Repair/Replacement

If you determine the MAF sensor is defective, it must be replaced. No repair or adjustment is possible.

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