![]() ![]() ![]() While diagnosing such problems are beyond the scope of this text, remember that intake manifold tuning valve failures, valve-timing problems, and restricted intake or exhaust systems usually reduce airflow through the engine. For example, a reverse pulse wave in the intake duct caused by a poorly seating intake valve or cylinder misfire can momentarily reverse the airflow into the MAF. Turbulence in the intake air stream can also affect MAF sensor calibration. On the other hand, a large particle stuck on the resistor, such as an insect or particle of vegetable chaff, can cause the metal-film resistor to radiate more heat than it should, causing the MAF to overestimate intake airflow. This generally forces the MAF to underestimate the engine’s intake airflow. In most cases, contamination tends to insulate the metal-film resistor from the air stream, which makes it run hotter than normal. Photo 2: When not serviced correctly, some types of oiled-media aftermarket air filters tend to contaminate hot-wire MAF sensors. In most cases, false air leaks will cause low-speed stalling or rough-idling complaints. “False air” leaking through cracks in the ducting that connects the MAF to the throttle body is a common problem affecting MAF sensor calibration. Although there are different configurations of MAF sensors, most current hot-wire MAFs share the same basic operating principles. In other MAF designs, the IAT is located downstream from the MAF sensor. Some MAF sensors also include an intake air temperature (IAT) sensor that helps the PCM calculate air density. In some applications, the PCM translates the base data input into a grams-per-second (GPS) data line indicating the metric weight of the air flowing into the engine. This variation in current flow, which is a base data input, is then translated into a voltage or frequency signal that is sent as a secondary data input to the PCM. The amperage flow through the resistor changes because the electrical resistance of the resistor is responding to the cooling effects of rapidly moving air. In general, a “hot wire” MAF sensor produces an input to the PCM when a low-amperage electrical current is passed through a metal-film resistor suspended in the MAF’s air stream. ![]()
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