On four-cylinder engines, the intake air is heated by low air pressure behind the throttle valve. From there, through a suitable hose, this low pressure acts on the diaphragm valve, which opens the heated air damper in the intake manifold (see illustration 6.0).
The intake air temperature sensor on the air filter housing is connected to the warm air damper circuit and shuts off the warm air supply at an ambient temperature of +35 - +45°C (Mono-Motronic injection system) or at +20 -+30°С (Digifant injection system) (see illustration 6.0a).
The position of the warm air damper for vehicles with five- and six-cylinder engines is controlled by a thermostat, which ensures that the damper is fully open at ambient temperatures of -20°C. As the ambient temperature rises, the warm air damper gradually closes. It closes completely at an ambient temperature of +5°C.
If the air heating does not function properly, this can lead to engine malfunctions. In the cold season, this is expressed as follows:
- poor idling of a cold engine after starting it in the warm-up phase;
- poor transition of the engine to a different mode of operation. Engine «chokes».
During the warm season
- reduction in effective engine power. The car does not accelerate to maximum speed;
- increased fuel consumption.
To check air heating on vehicles with four-cylinder engines:
1. Remove the hose from the brass or knurled fitting.
2. Blow out the hose with your mouth. In this case, you will hear how the valve opens on exhalation and closes on inspiration. If the damper does not work in this way, then check its ease of movement, and the hose itself and the membrane valve for tightness. If everything is normal, then the next step is to check the intake air temperature sensor itself.
3. Disconnect the hose from the throttle fitting. Blow air through the hose with your mouth. The hose must not be blocked.
4. Heat the intake air temperature sensor with a hair dryer to a temperature above 45°C.
5. Blow out the hose. It must be covered. Otherwise, replace the intake air temperature sensor.
Air heating in vehicles with five- and six-cylinder engines is checked as follows.
6. Remove the air supply hose from the air filter cover.
7. Shine a flashlight into the intake manifold. Depending on the ambient temperature, the damper should open or close access to heated air (see illustration).
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