| Mass Air Meter |
Article Index for Mass |
Website Links For Mass |
Information AboutMass Air Meter |
|
DESIGN The MAF meter consists of a housing and a Sensor which measures the Airflow through the housing. The MAF meter is placed between the Air Filter (which must be of the paper type to avoid any fluids reaching the wire) and Throttle Body on most vehicles so it can measure the air flowing into the engine. The sensor is a circuit designed to keep a heated wire at a constant temperature. The voltage in the circuit is dynamically adjusted from 0 to 5 volts to account for heat lost due to airflow. The more air that flows across the wire, the greater the heat loss and the greater the required voltage is to keep the wire at a constant temperature. As a result, the voltage required to keep the wire at the constant temperature can measure the mass of air moving across the sensor. MAF meters supply the ECU with a voltage from 0 to 5 Volt s that represents a measured airflow through the meter. A MAF transfer function tells the ECU how to transfer this voltage into a unit of measure for airflow. For example, if the ECU measured air in "pounds per minute," a MAF transfer function would tell the ECU that 3 volts from the MAF meter is equivalent to 10.9 pounds/min of air flowing into the engine. In most cases, a MAF Transfer Function is represented by a look up table in the ECU program. The output of the MAF transfer function is used to calculate two very important components of internal combustion engines: the ignites the air fuel mixture, the combustion process increases the pressure and temperature in the Cylinder . The rate of Combustion in the cylinder is dependent partly on what the AFR is in the Combustion Chamber . A richer AFR will combust slower and a leaner AFR will combust faster. A proper AFR will move the pressure peak to where there is more leverage on the Crankshaft and results in more power. To deliver the proper fuel, the ECU must be able to calculate the amount of air that enters the combustion chamber. If the MAF transfer function is not properly calibrated, the actual air fuel ratio will not be the same as the air fuel ratio commanded by the ECU. Another controlling factor of optimized engine performance is spark advance. Spark advance is calculated in part using engine RPM and Volumetric Efficiency (VE). Volumetric efficiency is based on the amount of air entering the combustion chamber, which is derived from the MAF transfer function. Spark advance can be defined as how many degrees in advance of top dead center (TDC), the air fuel mixture in the combustion chamber is ignited. Once the right AFR is achieved, proper spark advance controls the combustion process so the cylinder pressure peaks at the right rod/crank angle. Increased leverage on the crank means more power at the wheels. If cylinder pressure peaks much sooner, Detonation and loss of power occur. If it peaks much later, a significant loss of power is the result. When the MAF transfer function is not calibrated, proper spark advance cannot be calculated. Some vehicles also have the intake air temperature sensor (IAT) incorporated into the MAF sensor. MAINTENANCE With the increased popularity of reusable oiled air filters, mass air meters are more prone to oil and dust sticking to the wires that measure air flow. A dirty mass air meter can cause a rough idle, decreased performance, and computer codes among other problems. Most can be cleaned with spray electrical contact cleaner. Instructions for the cleaning mass air meter: Ford F150: http://www.fordf150.net/howto/clean-maf-mass-airflow-sensor.php Ford Mustang Cobra: http://www.svtsnake.com/tech/mafclean.html |
|
|