Sensors of mass air flow rate, which are used in various distributed fuel injection systems, are divided into two main varieties: wire and ceramic. Although they are slightly different in design, both types of sensors measure the volume and density of air entering the engine, so the computer can calculate how much fuel necessary to maintain the correct fuel mixture. In this article, we will analyze the principle of operation of the DMRV, as well as methods for diagnosing the sensor.
The principle of operation of the mass air flow sensor.
Sensors of mass air flow rate do not have moving parts. Unlike lobed ballooners in which the spring -loaded valve is used, an electric current is used in the sensors of mass air flow rate to measure the air flow. A sensitive element, which is either a platinum wire or a mesh of nickel foil, is heated by an electric current to maintain a higher temperature than the temperature of the incoming air. In the case of a ceramic MAF, the net is heated by 75 ss of above the ambient temperature of the incoming air. In the wire system, the wire is heated to 100 with the above -high environmental temperature. Since the air passes through the sensor, it cools the element and increases the current necessary to maintain the temperature of the element. Because the cooling effect is associated directly with the temperature, density and humidity of the incoming air, the amount of current required to maintain the element hot, directly proportional to the air “mass” entering the engine.
Output signal of the mass flow sensor.
The sensor MAF readings are displayed on the computer and depends on the type of sensor used. The wire version, which Bosch introduced back in 1979, generates an analog voltage signal that changes from 0 to 5 volts. The output voltage at idle, as a rule, is from 0, 4 to 0, 8 volts and increases to 4, 5 – 5, 0 volts with a completely open throttle.
The ceramic sensor, which AC Delco introduced in 1984, at the exit produces rectangular impulses of variable frequency. The frequency range is from 30 to 150 Hz, 30 Hz at idle and 150 Hz for a completely open throttle.
Another difference between the wire and ceramic sensors is that the Bosch wire system has a self -cleaning cycle, where the platinum wire heats up to 1000 s for one second after the engine is drowned out. Instant current surge is controlled by an on -board computer through a relay to burn pollution that prevents the sensor ability to read income air masses for sure. Therefore, a dirty air filter-view No. 1, for a mass air flow sensor.
Of course, do not forget the basics, such as engine compression, vacuum, fuel pressure, ignition, etc. D., since problems in any of these areas can provoke such symptoms of controllability.
Diagnostics of the sensor of mass air flow rate.
In addition to diagnosing the sensor using scanning, there are also ways to identify DMRV malfunctions.
Unlike lobed sensors with their movable valves, MAF does not have moving parts, so it essentially essentials to find out that the device is working normally, it is a day out
S signal of the sensor, or its influence during the operation time of the injector.
On the Bosch system, the output voltage can be read directly
a voltmeter, when submitted to the corresponding terminals. If the voltage readings are outside the range, or if the voltage at the output of the sensor does not increase when the throttle is open when the engine is running, the sensor is faulty and needs to be replaced. Dirty wire (which may be the result of defective self
Torn or burned wire leads to non -operational sensor. Crossing circuits or external pollution) can make the sensor slow to the response of a change in air flow.
The power supply to the MAF sensor is provided through two relay (one for wire, the other for the cleaning cycle), so check the first relay if the MAF-does not work or reacts slightly.
On the GM system, the MAF sensor, there are several ways to quickly. Sake an analog voltmeter to the corresponding connector of the output signal of the MAF sensor. At idle, the sensor must steadily issue 2, 5 volts. Press the sensor slightly and pay attention to its testimony. A good sensor should not show any changes. If there are jumps and / or engine for a moment stalled, the sensor is faulty and needs to be replaced. You can also check it, heating with a hairdryer and repeating the test.
Another way to check the MAF sensor is to measure the time of the injector. Use an oscilloscope or multimeter that measures the time in milliseconds, connect the device to any outlet output (one nozzle connector is the power voltage and the other circuit). Look at the duration of the injector pulses in idle mode (or during the engine turning, if the engine is not started). The injector time varies depending on the brand of the car, but if the sensor of mass air flow rate does not reproduce the signal, the injector will work about four times longer than usual (possibly, the fuel mixture is too rich for launch).