About Airflow Meters
Air mass meters are also commonly referred to as air flow meters, Maf senors and airflow meters. They measure the mass of the air flowing into the engine. The air mass information is necessary to calculate and deliver the right amount of fuel to the engine.
A mass air flow sensor is used to find out the mass of air entering a fuel-injected internal combustion engine.
The Air mass information is necessary for the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with temperature and pressure. In automotive applications, air density varies with the ambient temperature, altitude and use of a turbocharger and this is an ideal application for a mass sensor.
Mass air flow sensors don’t employ technology that measures air mass directly. However, with an additional sensor or two, the engine’s air mass flow rate can be accurately determined.
Mass air flow sensors are used almost exclusively on electronic fuel injection (EFI) engines, and output a 0.0- 5.0 volt or a pulse-width modulation (PWM) signal that is proportional to the air mass flow rate as well as containing an intake air temperature (IAT) sensor incorporated into their housings.
When a MAF is used in conjunction with an oxygen sensor, the engine’s air/fuel ratio can be controlled very accurately. The MAF sensor provides the open-loop predicted air flow information (the measured air flow) to the ECU, and the oxygen sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass.
Air Flow Meters are a common problem
Air Flow Meters measure the amount of air passing into the engine from which the computer can work out how much fuel to add to get the perfect mixture for that specific throttle opening; the computer does this by referring to a map in its memory.
The Air Flow Meter works by seeing how much current it takes to keep a wire at a specific temperature. However it is a sensitive instrument and it can be contaminated by oil (often used in aftermarket performance air filters), damaged by excess vibration caused by broken air through which contamination gets in, minute particles of dust and pollen etc, because of this contamination, the voltage will read less thus giving the ECU the wrong voltage output, this will in turn over or under fuel the engine making the car harder to start, the tick over will be lower this will in turn make the car stall, use more fuel, and give lower performance.
The fault will often not be shown on diagnostic system as the meter will still be operating within the limits the computer believes are OK, but putting the correct amount of fuel in for idle when the throttle is fully open will result in a very weak mixture and thus a lack of power.
Most airflow meters will read 0.98 volts when the ignition is turned on, when the car is started and running on tick over, the voltage should be 1.21, rising to 4.5 to 5 v depending on the make and model most airflow meter peak between 4.5,5 volt around 2500rpm. To do this you only need a cheap volt meter set to 5 volts, find the power import and the natural wires and the power out put.
The air flow meters will occasionally fail completely which will bring up a light on the dash and the symptoms described here are only the usual ones as we have known the fault to become apparent in other ways. Beware however as Lambda (or Oxygen) sensors in the exhaust can also give very similar symptoms to Air Flow Meters.
The easiest way to check if the Air flow meter is faulty is to unplug the wiring loom, start the car, if the car runs better then you have a airflow meter problem, its that easy, but do not drive the car like this it will cause you other problems, it can burn out the Lambda sensor and the catalytic converter (very expensive to replace) if you are in doubt, you can make use of our testing facility.
We can test up air flow sensors individually or in bulk, with full print outs and spec sheets, product sealing and dating. Please phone our Preston branch 01772 500 751