# Fuel system – SSP 442 The 1.6ltr. TDI Engine with Common Rail Injection System

> The fuel system of the 1.6 TDI and its common rail injection: components, pressure ranges and injection sequence.

- Web page: https://catalog.polo.blue/self-study/ssp-442-16-tdi-common-rail-engine/fuel-system/
- Original document (PDF): https://cdn.polo.blue/files/SSP442-1.6-TDI-CAYA-CAYB-CAYC-engine.pdf

## Fuel system (Golf 2009)

![Fuel system (Golf 2009)](https://catalog.polo.blue/instructions/ssp-442/7d7a8c38165b7aff.webp)

![Fuel system (Golf 2009)](https://catalog.polo.blue/instructions/ssp-442/dc3b39055510a46e.webp)

- **1** **Fuel system pressurisation pump G6**

The fuel system pressurisation pump constantly delivers fuel to the supply line.

- **2** **Fuel filter with pre-heater valve**

The pre-heater valve prevents the filter becoming clogged with crystallising paraffin crystals at low outside temperatures. (The pre-heater valve is mounted separately in the Polo 2010.)

- **3** **Pre-supply pump**

The pre-supply pump is part of the high-pressure pump and delivers the fuel from the supply line to the high-pressure pump unit.

- **4** **Fuel temperature sender G81**

The fuel temperature sender measures the current fuel temperature.

- **5** **High-pressure pump**

The high-pressure pump generates the high fuel pressure required for injection.

- **6** **Fuel metering valve N290**

The fuel metering valve controls on demand the quantity of fuel to be compressed.

- **7** **Fuel pressure regulating valve N276**

The fuel pressure regulating valve adjusts the fuel pressure in the high-pressure area.

- **8** **High-pressure accumulator (rail)**

The high-pressure accumulator stores the fuel required for injection into all cylinders under high pressure.

- **9** **Fuel pressure sender G247**

The fuel pressure sender measures the current fuel pressure in the high-pressure area.

- **10** **Pressure retention valve**

The pressure retention valve is used to stabilise the pressure in the return line to avoid fluctuations at the injectors and ensure the function of the piezo injectors. It keeps the pressure in the return line almost constant.

- **11** **Injectors N30, N31, N32, N33**

The injectors inject the fuel into the combustion chambers.

> The fuel system components are explained over the following pages.

## Common rail fuel injection system

The common rail fuel injection system was developed by Volkswagen and Continental. It is made up of:

- The engine control unit
- The injectors
- The high-pressure accumulator (rail)
- The fuel pressure sender
- The fuel pressure regulating valve
- The high-pressure pipes
- The high-pressure pump

The high-pressure pump consists of:

- The mechanical pre-supply pump
- The fuel metering valve
- The high-pressure pump unit

The common rail injection system allows optimum and efficient mixture formation and combustion. The following always applies: The higher the injection pressure, the smaller the droplets of fuel and the better the mixture formation. The basic feature of the common rail system is that the injection pressure (max. 1600bar) can be generated regardless of the engine speed and the injection quantity.

![Common rail fuel injection system (S442\_210)](https://catalog.polo.blue/instructions/ssp-442/66c250417e61bb34.webp)

The pressure generation and fuel injection are separated with the aid of the storage volume in the high-pressure accumulator (rail). The pressure is generated by a radial-piston type, high-pressure pump that conveys the fuel to the high-pressure accumulator (rail).

The injectors are connected to the high-pressure accumulator by short high-pressure pipes. Being the centrepiece of the system, the injectors have the task of injecting the fuel into the combustion chamber.

![Common rail fuel injection system (S442\_254)](https://catalog.polo.blue/instructions/ssp-442/9e23d0f9e0efc68b.webp)

A pulse sent to the injector by the engine control unit at the right time initiates the injection process. The opening duration and system pressure determine the injection quantity. In addition, the fuel can be divided into several individual injections per combustion cycle:

Very small quantities of fuel in the pilot injections are followed by the main injection and then several secondary injections for active regeneration.

While the pilot injections make the rise in pressure in the combustion chamber more constant and thus reduce the combustion noise, the secondary injections are intended for exhaust gas treatment. Together with the powerful control unit and the injectors with small tolerances, the common rail injection system clearly reduces consumption and emissions. At the same time, it increases the engine power and allows quieter running.