Is Toyota RAV4 1 1 intake metering sensor suitable for cleaning?

Some car owners know that the throttle can be cleaned and will choose to clean it every 30,000 kilometers or so. But few car owners know whether the air flowmeter can be cleaned. Actually, it can be cleaned. 20 1 1 Toyota RAV4 air flowmeter (intake air metering sensor mentioned in the title) is also applicable, and many maintenance technicians working in Toyota 4S shop will.

Structure and principle analysis of the air flowmeter of this vehicle.

20 1 1 Toyota RAV4 adopts l-type fuel injection electronic control system and hot-wire air flowmeter. The sensor can be used to detect the air intake of the engine, and the ignition time and fuel injection pulse width can be determined by the engine electronic control unit. The sensor also integrates an air temperature sensor to correct the fuel injection quantity. As shown in the figure below, the blue circle is the temperature sensor, the red circle is the sensing part of the air flowmeter, and the part shown by the arrow is the control module.

Let's analyze the internal components of the sensor, as shown in the figure below. The sensing part of the red circle above is actually two resistors, namely a platinum hot wire and a temperature sensor. When the engine is working, the engine ECU will apply a certain current to the platinum hotline to make it reach the specified temperature, so it is called the hotline. The temperature sensor is called cold wire, which can provide a reference signal of heating current for hot wire. During the operation of the air flow meter, the temperature of the hot wire is higher than that of the cold wire 100 degrees.

Resistors RB and RA are installed in the module. These two resistors are very high and will not be affected by temperature (they can be considered as the same resistor), where the voltage of 12V is provided by the battery through EFI relay at point C and the grounding point at point D.. When air flows through Rh hot wire and Rk cold wire, its resistance will change. At this point, the voltage at point B will decrease. In order to keep the voltage balance between point A and point B, the control transistor will increase the voltage through Rh until the resistance of RH increases to bridge balance. The voltage change is proportional to the air flow, and then the sensor informs the engine electronic control unit of the voltage change, and the electronic control unit calculates the intake air according to the numerical value.

Reasons for cleaning air flowmeter

The following figure shows the installation position of the sensor, which is located behind the air filter. The air passing through the air flow meter is filtered by the filter. In addition, every time the ignition switch is turned off, the ECU will instantly heat the hot wire to 1000 degrees for about one second, just to burn off the impurities attached to the hot wire.

However, after a period of use, due to the influence of vehicle environment and vehicle condition, some car owners do not pay attention to vehicle maintenance and do not replace the air filter for a long time. Not only there is dust on the intake pipe, but also the recoil of exhaust gas and the influence of ventilation pipe of PCV crankshaft forced ventilation system will produce mixed substances such as sludge and carbon deposition. At this time, the self-cleaning function of the sensor may not work, and the substances attached to the sensor will affect the temperature change of the hot wire, thus changing the output voltage signal and affecting the measurement accuracy. If the flowmeter is broken, the engine ECU will replace it with the signals of throttle position sensor and crankshaft position sensor. There is little difference in power during driving, but the control accuracy will be a little worse.

Empty and dirty air flow meters will affect the detection of intake air, resulting in an increase in fuel injection quantity (fuel injection time) and high fuel consumption. For example, the engine speed of this car is 1200r/min, the air intake is 5.43g/s, and the fuel injection quantity is 2.9ms. That is to say, when the air-fuel ratio is close to the ideal air, the fuel consumption is 5.43g/[k0/], and the fuel injection time of the fuel injector is 2.9ms.. ..

As shown in the following figure, the air flow meter signal is low or the intake air volume is too large or too small relative to the normal value because the dirt deviates from its characteristics. At this time, ECU will correct the fuel according to the oxygen concentration in the exhaust gas to control the air-fuel ratio within a certain range, but the effect of this fuel correction is limited, which often leads to the fuel injection exceeding the normal range. If the mixture is too rich or too thin, it will burn incompletely in the combustion process, which will lead to faults such as insufficient power and excessive displacement, so the air flowmeter is dirty and needs to be cleaned.

How to judge that the air flowmeter needs cleaning?

We can judge by reading the data flow of the air flow meter. As shown in the following figure, the parameters of MAF air flowmeter are described in the maintenance manual, which are 0.54-4.33 g/s at idle speed and 3.33-9. 17 g/s at 2500rpm. If this data is exceeded, if the read data stream is 0g/s, no 12V power supply or signal output line is open; If it is 27 1 g/s, the ground terminal of the sensor is open. If the wiring is normal, the sensor is damaged and needs to be replaced.

How to clean the air flowmeter correctly

Cleaning air flowmeter mainly includes cleaning hot pipeline and cold pipeline. The cleaning method is simple. First, remove the air flow meter. The air flow meter on the car is fixed with two screws and can be disassembled and loosened. In the choice of cleaning agent, it is enough to buy carburetor cleaning agent or throttle cleaning agent (this is also what maintenance technicians in 4S stores do). Some car owners are afraid that the carburetor cleaner will be corrosive and damage the resistance wire inside, and they can also choose expensive high-precision electric cleaner.

When cleaning, be sure to clean it in place to avoid damaging the resistance. After cleaning, blow clean with compressed air. If you can't use compressed air, you can also dry it naturally, or use the air conditioner of the hair dryer to dry it. After cleaning, drive out for a spin and run 10 km or more. It is normal not to report fault codes. In this process, the electronic control unit will automatically learn the data of the flowmeter.

abstract

20 1 1 Toyota RAV4 air flowmeter is suitable for cleaning. We can check the data flow of the air flow meter to determine whether the sensor needs cleaning. When cleaning, clean the hot and cold pipes. After cleaning, we should drive out for a run and let the computer automatically restore the working mode of the sensor.

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