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The fuel system handles four main functions necessary for proper engine operation: (1) it provides storage space for the fuel; (2) it delivers fuel to the engine; (3) it admits filtered air to the engine to be mixed with fuel; (4) it mixes fuel and air in precise proportions and delivers the mixture to the cylinders as a combustible vapor. On all gasoline-fueled cars covered by this manual, the fourth function is performed by one of five types of sophisticated fuel injection systems.

Unlike a carburetor, which depends on the velocity of the incoming air to vaporize the fuel and draw it into the engine, a fuel injection system injects atomized fuel into the intake air stream under pressure. This method of active fuel metering means that the fuel mixture entering the engine can be controlled more precisely and used more efficiently, yielding improved driveability, fuel economy, and performance.

Five different types of gasoline fuel injection systems are installed on the cars covered by this manual. Each has its own unique features and methods of operation, but all achieve the same basic result of supplying air and fuel to the engine in the proper amounts at the proper time. Although at first look these systems appear complicated, they operate on simple principles and can be understood with a little study. This section provides separate descriptions of each system, making it possible to identify and understand the system used on a particular car. Troubleshooting and repair are covered in detail. Test procedures for individual components also explain their function, so that the purpose of each test can be understood.

Special equipment is necessary for some fuel injection service. Please read the information carefully before beginning any test or repair. If you do not have the equipment or the experience necessary to do the job accurately, we suggest leaving those tests or repairs to an authorized Volkswagen dealer or other qualified repair shop. We especially urge you to consult an authorized Volkswagen dealer before beginning any work on a car that may be covered wholly or in part by any of the extensive warranties issued by Volkswagen United States, Inc.

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