Sensors of the fuel system of diesel engines TDI (Audi 80 B4)

Accelerator Pedal Position Sensor

TDI engines do not have an accelerator cable. The potentiometer transmits information about the accelerator pedal position to the control unit. To prevent the control unit from making incorrect decisions (for example, if a defect causes the unit to believe that the pedal is in the "Full Accelerator" position), the brake pedal is connected to an additional brake light switch, which prevents the control unit from recognizing the "Full Accelerator" information when braking. The same applies to the clutch pedal.

Engine speed and TDC sensor

This inductive sensor is located under the oil filter flange on the crankcase and reads the number of revolutions from the contact ring on the crankshaft. The contact ring has 4 grooves, each of which corresponds to TDC (see illustration 10.0a).



Needle lift sensor in cylinder #3 injector.



This sensor informs the control unit of the exact start of injection at the current moment (see illustration 10.0b).



Intake air temperature, intake manifold temperature, coolant temperature and fuel temperature sensor

These sensors are located in the air flow meter, in the air guide pipe, in the coolant outlet pipe and in the high-pressure fuel pump itself (see illustration 10.0b).

Air flow meter

Information about the amount of air admitted is needed by the control unit to calculate the fuel required for injection. The measurement of the volume of incoming air occurs as follows. The valve shutter of the air flow meter deflects depending on the incoming air volume. This movement of the shutter is recorded as a change in resistance (potentiometer) and is recognized by the control unit as an electric current value (see illustration 10.0g).

Air mass flow meter

This sensor is installed on cars manufactured since the end of 1993, as well as on cars with an automatic transmission. It performs the same function as the air flow meter, which it replaces, but the measurement is performed differently. A film installed in the air flow path is heated. Depending on its mass, the incoming air cools this film to a greater or lesser extent. The film resistance changes and the control unit again receives an electrical signal of a certain value.

Intake Manifold Pressure Sensor

This sensor is located at the rear of the engine compartment on the right side and is connected by a hose to the charge air cooler (intercooler). In cars with automatic transmission and in cars with manual transmission produced since the end of 1993, this sensor is an element of the control unit. The specified sensor is responsible for information about the boost pressure and regulation of the injection volume.

Fuel filter condensate level sensor

This sensor is not installed on vehicles with automatic transmission. Vehicles with manual transmission were equipped with this sensor until the end of 1993. (see illustration 10.0d).

Boost pressure valve

The boost pressure is regulated by an electromagnetic valve that opens a pressure-reducing valve. In earlier cars, it is located at the rear of the engine compartment. In cars with an automatic transmission, as well as in cars with a manual transmission produced since the end of 1993, it is located on the right in the front of the engine compartment.

EGR valve

The exhaust gas recirculation valve together with the oxidation catalyst ensures that the content of harmful substances in the exhaust gas is within the existing standards and requirements. Unlike the 55 kW diesel engine with swirl chamber injection, in which the exhaust gas recirculation is carried out according to the "Inlet-Outlet" principle, in TDI engines intermediate exhaust gas values can be produced using recirculation.

Preheating device

The injection system control unit controls the preheating device depending on the engine temperature.