Fuel supply to the fuel system (Skoda Superb B6)

Petrol models

The fuel system consists of a rear-mounted fuel tank with a filler neck, a fuel supply module with a fuel gauge, a fuel gauge #2 with a jet pump, a carbon fuel vapor absorber, fuel lines, a fuel filter, and a fuel injection system controlled by an electronic engine control unit (ECM). The fuel injection system consists of a high-pressure fuel pump, a fuel distribution line, and injectors.

The fuel tank contains a fuel supply module, which is an assembly of a fuel level sensor and a fuel pump with a mesh filter. The fuel level sensor is designed to display the fuel level on the instrument cluster. The electric fuel pump is designed to create pressure in the low-pressure part of the fuel supply system. The on/off and performance of this pump (depending on the crankshaft speed and engine operating mode) the corresponding control module "J538" operates via a PWM signal, operating on the basis of information from the ECM. The mesh fuel filter is designed for the entire service life of the vehicle and does not require replacement.

The jet pump is designed to pump fuel to the fuel supply module from another part of the tank. Fuel reserve sensor No.2, combined with the jet pump, is designed to provide more accurate information about the fuel reserve.

In the event of an accident, the fuel shut-off function may be activated to reduce the risk of ignition of leaking fuel. This function switches off the fuel pump at the level of its relay.



To improve engine starting performance, the fuel pump relay is activated for two seconds when the driver's door is opened to pre-pressurize the fuel supply system. Therefore, for safety reasons, the fuel pump control unit connector should be disconnected during repairs without disconnecting the battery.

To ventilate the fuel tank, vent valves are used to remove fuel vapors to the EVAP system canister (see Part B).

The injection pump is designed to create high fuel pressure to implement the principle of direct fuel injection (FSI). The injection pump is driven by a pusher: on the 3.6 l engine, the pusher is driven by a 2-cam eccentric with a toothed transmission from the timing chain, and on other engines, the pusher is driven by a separate camshaft cam.

Fuel from the injection pump accumulates in the fuel distribution line, equalizing its pressure, and is then injected directly into the combustion chambers through the injectors. The moment and duration of fuel injection are determined by the ECM using signals from various sensors (see Section 2).

The location of the power supply system components is shown in illustrations 1.1ag.

Diesel models

The fuel supply system consists of a rear-mounted fuel tank with a filler neck, a fuel supply module, fuel lines, a fuel cooler, a fuel filter, an additional fuel pump, and an electronic sequential distributed fuel injection system controlled by an electronic engine control unit (ECM). The distributed sequential fuel injection system on TDI-CR models includes a high-pressure fuel pump (HPFP), a fuel distribution line "Common Rail", piezo injectors, pressure fuel pipes and return fuel lines. The distributed sequential fuel injection system on the "TDI-PD" models includes: a fuel pump (combined with a vacuum pump into a single "tandem" pump), feed and return lines in the cylinder head and unit injectors.

[Information copied from the resource: SKODABOOK.ru]

The locations of the fuel system components are shown in Figures 1.2a-b. The fuel supply system diagram is shown in Figure 1.3. The following description applies to models with a "TDI-CR" fuel distribution line.







The fuel delivery module is an assembly of the electric booster pump and fuel level sensor, and also provides connections for delivering fuel to the auxiliary heater (see Chapter 3). The electric booster pump is designed to continuously supply fuel from the tank to the filter. The fuel reserve is displayed on the instrument cluster (see Chapter "Controls and operating techniques").



The fuel filter protects the fuel supply system from contamination by water and other foreign particles and, therefore, from premature wear. The fuel filter must be replaced periodically (see Section 23 Chapter 1). The filter has a built-in preheating valve, which prevents the filter from becoming clogged with crystallizing paraffins at low ambient temperatures.

The additional fuel pump is designed to supply fuel from the low-pressure circuit to the high-pressure fuel pump under a pressure of at least 5 bar, which is necessary for the high-pressure fuel pump to operate in any mode. This vane-type pump is controlled by a relay from the ECM. If the additional pump fails, the engine power is reduced and it cannot be started.

A mesh filter and fuel temperature sensor "G81" are installed between the additional fuel pump and the high-pressure fuel pump.

The injection pump, driven by the timing belt from the crankshaft, increases the fuel pressure to a maximum of 1800 bar and delivers it through one pipe to the fuel distribution line, where the fuel pressure is equalized for all injectors and monitored by the fuel pressure sensor.

High fuel pressure is regulated by the so-called "dual regulation algorithm": depending on the engine operating mode, either through the fuel pressure regulator valve or through the fuel metering valve. The valves are controlled by the engine control unit using a pulse-width modulated (PWM) signal.

The fuel pressure regulator valve is adjusted when starting the engine and to warm up the fuel. A high fuel temperature is required for good mixture formation in the combustion chamber with a slight ignition delay. In order to quickly warm up the fuel when the engine is cold, the high-pressure fuel pump supplies and compresses more fuel than necessary, and the excess heated fuel is fed back through the pressure regulator valve and the return fuel line. If the fuel pressure regulator fails, the engine cannot operate, since the pressure required for fuel injection cannot be created.



The adjustment via the fuel metering valve is carried out at high injection volumes and high pressure in the fuel distribution line. This reduces the power consumption of the high-pressure fuel pump and prevents unnecessary heating of the fuel. If the fuel metering valve fails, the engine power decreases, and the engine management system operates in emergency mode.

Pressure fuel lines (metal tubes) manufactured with pre-set lengths and bending radii in the required places; such fuel lines should be installed in such a way that they are not subject to any stress.

The injectors inject fuel under high pressure directly into the combustion chambers. The timing and duration of fuel injection are determined by the ECM using signals from various sensors (see Section 2).

Excess fuel from the injectors returns to the fuel tank through the injector return lines, the pressure holding valve and the fuel pump. The purpose of the fuel pressure holding valve is to maintain the pressure in the injector return lines required for the injectors to operate. Do not disconnect the fuel pressure holding valve while the engine is running to prevent damage to the injectors. The injector return fuel lines are only replaced together with the pressure holding valve. If the fuel holding valve and the injector return lines have been replaced, after starting the engine, let it idle for about two minutes to remove air from the fuel supply system.

Fuel injection system with fuel distribution rail "Common Rail", compared to the injection system with a distributor fuel injection pump, it has the following distinctive features:

• injection pressure can be freely selected and adapted to the corresponding engine operating mode;
• high injection pressure (up to 1800 bar) creates conditions for good mixture formation;
• flexible batch injection process with multiple pre- and post-injections;
• low fuel consumption;
• low level of emissions of harmful substances;
• smooth engine running.

Injection system "Common Rail" it involves a variety of injection control algorithms in order to adapt the pressure and injection process to the engine operating mode. At the same time, such a system fully complies with the ever-increasing requirements for reducing fuel consumption, reducing the level of harmful emissions and increasing the smoothness of the engine.

To improve engine starting performance, the fuel pump is turned on for two seconds when the driver's door is opened to pre-pressurize the fuel supply system. Therefore, for safety reasons, during repairs without disconnecting the battery, the fuel pump relay fuse should be removed or the fuel supply module connector should be disconnected.

Fuel Saving Tips

Driving style has a significant impact on fuel consumption. Below are some tips for saving fuel.

• Once the engine starts, move off immediately, even if it is in freezing temperatures (do not allow a cold engine to run at high speeds and do not drive at high speeds until the engine has warmed up).
• If the vehicle is stopped for more than 40 seconds, turn off the engine.
• Always drive in the highest gear possible for the given speed.
• When driving long distances, maintain a steady speed whenever possible. Avoid driving at high speeds and do not brake unnecessarily.
• Do not carry unnecessary cargo in your vehicle.
• Check the air pressure in your tires and do not allow the pressure to drop too low.