(1) cleaning after the hot wire and hot film are dirty
If the engine has "backfire" fault, it often causes serious harm to the air flow sensor. Due to the reverse flow (i.e. "tempering") of the engine air flow in the intake manifold, which contains carbon particles, these carbon particles are easy to adhere to the sensing elements of the air flow sensor, and have the following consequences: when idling, the signal of the air flow sensor is too large, while when accelerating and heavy load, the signal is too small.
The inspection method of whether the hot wire has self-cleaning ability is: remove the air filter, and observe the hot wire from the air inlet of the air flow sensor. If the hot wire can not be seen to emit a reddish glow for about 1s after the engine is shut down for 5S, it indicates that the self-cleaning ability of the hot wire has been lost.
After the hot wire (hot film) is polluted, it can be heated and idled. Remove the filter screen of the air filter and spray hot wire or hot film directly with carburetor cleaning agent to remove the carbon deposit on it.
Many models use the hot film air flow sensor produced by BOSCH company. Its core part is composed of an integrated circuit (D / a conversion circuit) and Wheatstone bridge without voltage stabilizing circuit. Therefore, when the power supply voltage is too high or the instantaneous high voltage occurs, the hot film air flow sensor is easy to burn out. The reason why the peak voltage of the circuit is too high (more than 16V) is that the storage battery is vulcanized seriously, which reduces its capacity and cannot absorb the peak voltage of the generator. Therefore, the vulcanization of the storage battery is one of the reasons for the damage of the hot film air flow sensor. The solution is to install a 7812 three terminal voltage stabilizing integrated circuit at the front end of the hot film air flow sensor.
(3) block the entrance of air without measurement
These abnormal ways include: the intake pipe is broken, the vacuum hose is loose, and the intake manifold and cylinder head are not tightly sealed. If the above situation exists. Part of the air will enter the cylinder directly without the measurement of the air flow sensor, resulting in the imbalance of the engine mixture.