How to Test a Mass Air Flow Sensor for 2001 Ford Sport Trac

The mass airflow sensor on a 2001 Ford Sport Trac truck is designed to signal the amount of air flowing into the engine as a result of the load on it. It is a hot wire sensor where the computer energizes the wire to raise it to a predetermined temperature. As airflow increases over the wire, it requires more voltage to maintain its temperature and less voltage as the airflow slows. This varying voltage is what the computer senses and makes adjustments to the fuel injection and ignition accordingly.

Instructions

1

Locate the mass airflow sensor located on the passenger's side in the air filter outlet tube. Look for the wiring harness connector on the side of the air cleaner tube. It will have four or six wires. Some mass air flow sensors also incorporate an intake temperature sensor, but this is of no consequence for checking the mass air flow sensor. The temperature sensor wires are the outside wires on the connector. A bad or contaminated mass airflow sensor on a Ford truck will cause lean (too much air and insufficient fuel) mixture problems such as valve ping due to preignition under a load, dieseling when the engine is shut down, high cylinder head temperatures and lack of power. This truck is known to have problems with the sensor wire becoming contaminated. When this happens, the computer mistakes this signal as a rich mixture, so the computer leans the mixture. Before condemning the sensor, clean it and retest it.

2

Clean the mass airflow sensor for expedience before further testing. This may correct the problem with no need to proceed any further. Unsnap the air cleaner box and remove the lid. Lift the air cleaner element out of the box, exposing the mass airflow sensor intake.

3

Clean the hot wire with this in mind: You are dealing with a wire the thickness of a hair. One straight shot against the wire will instantly remove it, making the sensor garbage. With the engine running, stand to the side of the sensor and spray short shots of spray against the lower lip of the intake to the sensor, allowing the engine vacuum to suck the cleaner into the intake past the hot wire. Keep spraying until half the can is used. Spray a little at a time in front so it can be drawn in over the wire, never directly on the wire. When finished, shut the engine off.

4

Verify whether the problem was corrected or if a new mass air flow sensor is needed. Looking at the wires in the mass airflow connector and counting from left to right, there are four wires. Connect the black voltmeter lead to a good ground. Use the sharp pointed probe on the red lead to pierce the first wire to the left on the connector. Always pierce the wire; never push the probe into one of the terminals.

5

Start the engine. If the sensor is good, the voltage should be between 0.46 to 2.44 volts. Have a helper slowly increase engine speed up to 3,000 rpm and slowly down to an idle. Watch very carefully at the voltage. It must increase steadily in unison with the throttle up to 5 volts with absolutely no dropouts or glitches in the voltage. Any erratic voltage reading indicates a bad sensor. The last test is to snap the throttle very quickly and watch the voltmeter. The voltage should rise suddenly, again in unison, and drop at the same rate as the engine rpm. If it hesitates or does not rise much, the sensor is bad.

6

Move the red voltmeter probe to the PCM -- which is the second wire from the left. Turn the key on. The voltmeter should display less than 100 mV or there is an internal short in the mass air flow. If the voltage was in the parameters, move the red voltmeter probe to the first wire all the way to the right of the connector. This is the power wire. With the key on, the voltage should be no less than 10.5. If the reading is less, the wire is corroded or shorted to the mass air flow sensor. Check this wire to the relay fuse and to the battery.

7

Test the computer ground circuit -- the wire running to the computer. The computer monitors the amount of power going to ground and regulates the amount of ground circuit. Place the black probe in the second wire from the left. Be extremely careful not to short this wire to ground as it will damage the computer fuel injection circuit. Place the red lead on the positive terminal on the battery. The voltmeter should display more than 10 volts. If the voltmeter displays 10 or less, there is a short in the wire to the computer. Repair the short and retest.