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Page 4

MAF check and Test before changing

Mass Air Flow Test is a very easy and simple test but there are a couple of things that have to be done first.

The most important thing to do first, is to make sure your MAF Sensor isn't contaminated with dirt and/or oil, since the tests in this article assume the MAF sensor isn't contaminated. Why? Because this MAF Sensor is a hot-wire type that easily becomes contaminated with dirt and stuff from the air filter not performing its job. Cleaning this type of Sensor is easy since the hot-wires are clearly visible to the eye (with the sensor removed).

This contamination will cause the sensor to produce a lower reading to the ECM (Engine Control Module = Fuel Injection Computer). The most common symptom of this contamination is a hesitation or a time-lag in engine responce that is felt after the accelerator pedal is depressed. As stated in the list at the beginning of this article, other symptoms may include but are not limited to: higher tailpipe emissions and diagnostic codes that may illuminate the "Check Engine" light.

If cleaning the MAF Sensor, use an electronics spray cleaner to do it with. This in itself may solve your problem. Don't use carb or brake clean spray. These solvents can damage the sensor. Also, don't attempt to physically clean the sensor with anything. Check your local autopart store, they will have MAF Sensor cleaning spray.

After having checked for contamination the other things that you must check for (and eliminate if present) are:

  1. That the engine does not have any vacuum leaks.
  2. That there are no ignition system misfires. A misfire condition will skew the results of the test you'll perform here.

If the above conditions exist, repairing them first will more than likely solve your vehicle's drive-ability issue without having to test the MAF Sensor, if not continue with the MAF Test .

We start by checking the Mass Air Flow (MAF) Sensor basics.

These are 12 Volts and Battery ground to the MAF Sensor. After that, we'll test the actual performance of the MAF Signal as the engine is running. Use a digital multimeter for all tests where a multimeter is called for.

The MAF Sensor produces an analog Voltage signal. At idle with the engine at its normal operating temperature, the MAF Sensor produces a signal of 1.0 volts to 1.7 volts. The MAF Sensor's operating voltage range is from .0 to 5 volts.

The MAF Signal's voltage is directly related to amount of air the engine is breathing. Common sense tells us that the engine will breathe in more air at 2500 RPMs than at an idle of 900 RPMs.

So keeping this in mind, the Voltage value on the multimeter will be greater at 2500 RPMs than at 900 RPMs

Now, when testing this Voltage signal, the important thing to know is not an actual volts number at a specific RPM, but to look for crazy and extreme fluctuations in the voltage signal that do not correspond to the actual air intake (RPM's) of the engine. For example: If at Idle the Voltage reading starts to spike up and down without you accelerating the engine.

Note these tests are not designed to diagnose an intermittent problem with the MAF sensor. They are designed to diagnose a hard fault with the sensor.

The very first thing that we'll do is check that the MAF Sensor is receiving 12 volts.

Again, the procedure I recommend to use (to accomplish all of the tests below) is to use a test probe that pierces thru' the wire's insulation
DO NOT insert anything into the female terminal.

Whatever method you use, the key here is not to damage the female terminal or the wire. Again, be careful. Use common sense and take all necessary safety precautions.

  1. Put the multimeter in VOLTS DC mode.
  2. Do not disconnect MAF Sensor Connector from the MAF Sensor.
  3. With the RED multimeter test lead and an appropriate tool, probe the MAF Sensor + Connector.
  4. With the BLACK lead of the multimeter probe BATT (-) negative terminal.
  5. Turn Key On with the Engine Off.

You should see 12 Volts on the multimeter. Do you have 12 volts?

CASE 1: Your Multimeter registered 12 Volts  Go on test.

CASE 2: Your Multimeter DID NOT register 12 Volts The MAF sensor is not the problem. Without power in this circuit, the MAF Sensor will not work.

Now we'll check that the MAF Sensor is getting a good ground. This Ground is provided by the ECM internally.

Be careful and take extreme care not to short-circuit this wire to ground or power as you're probing it.

You can test this circuit with the connector connected to MAF Sensor or not.

  1. Turn key to the OFF Position.
  2. Put the Multimeter in VOLTS DC mode.
  3. With the BLACK multimeter test lead and a wire-piercing-probe, probe the MAF sensor - connector
  4. Connect RED lead to the BATT (+) positive terminal.
  5. Turn the Ignition Switch to the RUN position.

You should see a voltage of 12 Volts. Do you have that?

CASE 1: Your Multimeter registered 12 Volts Go on with Test.

CASE 2: Your Multimeter DID NOT register 12 Volts The MAF sensor is not the problem. Without a ground in this circuit, the MAF Sensor will not work.

We'll check the MAF signal coming out of the sensor and going to the ECM with a multimeter.

Start the engine and let it reach it's normal operating temperature. You'll be using the Voltage reading you will obtain at idle as a base to diagnose the MAF Sensor.

The MAF Sensor must be connected to its connector to perform this test.

  1. With the key in the OFF position.
  2. With a suitable tool connected to the RED multimeter lead, probe the signal circuit of the MAF Sensor connector.
  3. Put the multimeter in VOLTS DC mode.
  4. Connect the BLACK lead to the Battery (-) Negative Terminal.
  5. Start the already warmed up engine.
  6. Note the Volts reading on your multimeter at idle. This reading may be stable (with only small fluctuations) or unstable with very extreme fluctuations. No matter what the instability in the reading, this will be your base reading.
  7. Accelerate the engine as you watch the multimeter's Voltage readings.
  8. The Voltage numbers should correspond to the amount of acceleration.
  9. Repeat this as often as you need to verify that the Voltage numbers on the multimeter rise smoothly every single time.
  10. If the MAF Sensor is good, these readings will not spike up and down crazily but will correspond to the amount of air the engine is breathing at the different RPMs you're accelerating the engine to.

Did the signal rise smoothly with each increase in engine acceleration and stay steady at idle?

CASE 1: Your Multimeter registered the indicated Voltage The MAF Sensor is functioning correctly.

CASE 2: Your Multimeter DID NOT register the indicated Voltage The MAF Sensor is defective. Replace MAF Sensor.

 

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