Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Volume Air Flow Sensor

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OPERATION



The volume air flow sensor is incorporated within the air cleaner; it functions to convert the amount of engine air intake to pulse signals of a frequency proportional to the amount of engine air intake, and to input those signals to the ECM. The ECM then, based upon those signals, calculates the amount of fuel injection and ignition timing.

The power for the volume air flow sensor is supplied from the MFI relay to the volume air flow sensor, and is grounded at the ECM. The volume air flow sensor, by intermitting the flow of the 5 volts applied from the ECM, produces pulse signals.

TROUBLESHOOTING HINTS



  1. If the engine sometimes stalls, try starting the engine and shaking the volume air flow sensor harness. If the engine, as a result of shaking the harness, stalls, incorrect or improper contact of the volume air flow sensor connector is the probable cause.
  2.  
  3. If, when the ignition switch is ON (but the engine is not started), the volume air flow sensor output frequency is any value other than zero, a malfunction of the sensor or of the ECM is the probable cause.
  4.  
  5. If idling is possible even though the volume air flow sensor output frequency is deviated from the standard value, the cause is usually a malfunction other than of the volume air flow sensor. For example:
    1. The flow of air within the sensor is disturbed. (An air duct is disconnected or the air cleaner element is clogged.)
    2.  
    3. Incomplete combustion within a cylinder is happening. (Malfunction of sparkplugs, ignition coil, injectors, compression pressure, etc.)
    4.  
    5. Air is taken into the intake manifold through a leaking gasket, etc.
    6.  
    7. There is an improper adhesion of the valve sheet on the EGR valve..
    8.  

  6.  

HARNESS TESTING



When performing these checks, use a harness side connector to fasten onto the different terminals.

2.4L Engines

See Figures 1 and 2

The 1993-95, rear-wheel drive 2.4L (California) Pick-ups have the same engine controls as the 3.0L engines. All other 2.4L engines are listed as 2.4L engines.

  1. Unplug the volume air flow sensor harness connector from the sensor itself. With the ignition switch ON , measure the power supply voltage to terminal 4 of the harness connector. If the voltage is not that of the battery (around 10-12 volts), repair or replace the harness between terminal 4 and the MFI relay, or check the MFI relay, otherwise go on to Step 2.
  2.  



Click image to see an enlarged view

Fig. Fig. 1: The volume air flow sensor harness connector terminal arrangement



Click image to see an enlarged view

Fig. Fig. 2: The sequence to check the volume air flow sensor-2.4L engines

  1. Measure the terminal voltage at terminal 3. If the voltage is 4.8-5.2 volts continue on to Step 3, otherwise repair or replace the harness from terminal 3 to the ECM terminal 10.
  2.  
  3. Turn the ignition switch OFF , and check for continuity of the ground circuit (terminal 5 on the volume air flow sensor harness connector). If there is continuity, continue on to Step 4, otherwise repair the harness between the volume air flow sensor terminal 5 and the ECM terminals 14 and 24.
  4.  
  5. Disconnect the ECM harness plug from the ECM. Check for continuity between the volume air flow sensor (terminal 7) and the ECM (terminal 57). If there is continuity, then the part is OK, otherwise repair or replace the harness between the two terminals.
  6.  

3.0L and 3.5L Engines

See Figures 3 and 4

  1. With the the MFI harness connector and the volume air flow sensor harness connector unplugged, check for continuity between the volume air flow sensor connector (terminal 4) and the MFI relay connector (terminal 4 for 3.0L 12 valve engines, otherwise terminal 2). Touch the ohmmeter probes to both ends of the harness. If there is no continuity, repair or replace the harness between the two components, otherwise go on to Step 2.
  2.  
  3. Check for continuity from terminal 5 of the volume air flow sensor harness connector to ground. If continuity is present, go on to Step 3, otherwise repair or replace the harnesses between terminal 5 of the volume air flow sensor and the terminals (17 and 24 for 3.0L 12 valve engines, otherwise 72) of the ECM.
  4.  
  5. Unplug the ECM harness connector. Check for an open or short-circuit between the volume air flow sensor harness connector terminals 7 and 3 and ECM terminals 57 and 10 (70 and 19 on 3.0L 24 valve and 3.5L engines). If a short or open-circuit is found, repair or replace the harnesses between the two connectors, otherwise go on to Step 4.
  6.  



Click image to see an enlarged view

Fig. Fig. 3: The sequence for checking the volume air flow sensor-3.0L and 3.5L engines

  1. Turn the ignition switch ON and measure the applied voltage from terminal 3 of the volume air flow sensor harness connector to ground. The voltage should be 4.8-5.2 volts, if it is not, then replace the ECM with a new unit, otherwise the volume air flow sensor is good. Plug all connectors back in and turn the ignition OFF .
  2.  

COMPONENT TESTING



Mitsubishi does not give testing procedures of the volume air flow sensor itself with an ohmmeter. To test this component an oscilloscope is needed. Due to the high cost, and special skills needed to operate the tool, have the system diagnosed by a dealer or reputable service facility.

REMOVAL & INSTALLATION



See Figure 4

The volume air flow sensor is located between the air cleaner and the air inlet hose. To remove the sensor, remove the air intake hose by loosening the screw-type hose clamp. Pull the air intake hose off of the sensor. Loosen the four nuts holding the sensor to the air cleaner assembly box and pull the sensor off of the air cleaner. When installing the sensor back onto the air cleaner box, use a new gasket and tighten the mounting nuts to 6-7 ft. lbs. (8-10 Nm).



Click image to see an enlarged view

Fig. Fig. 4: The location of the volume air flow sensor-all models similar

 
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