Volkswagen Air-Cooled 1970-1981 Repair Guide




See Figures 1 through 5

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Fig. Fig. 1: Location of fuel injection components used on Type 3 models

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Fig. Fig. 2: Schematic of the electronic fuel injection system used on 1970 and later Federal models and 1970-71 California models

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Fig. Fig. 3: Schematic of the electronic fuel injection system used on 1972-74 California models

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Fig. Fig. 4: Exploded view of the airflow controlled fuel injection system used on 1975-81 Type 1 and Type 2 models (Type 1 shown, Type 2 similar)

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Fig. Fig. 5: Schematic of the airflow controlled electronic fuel injection system used on 1975-81 models

The Bosch Electronic fuel injection system used on all Type 3 models, and on 1971-74 Type 4 models (except 1974 models equipped with an automatic), consists of two parts. One part consists of the actual injection components: the injectors, the fuel pump, pressure regulator, and related wiring and hoses. The second part consists of the injection controls and engine operating characteristics sensors: a manifold vacuum sensor that monitors engine load, trigger contacts used to determine when and which pair of injectors will operate, three temperature sensors used to control air fuel mixture enrichment, a cold starting valve for additional cold starting fuel enrichment, a throttle valve switch used to cut off fuel during deceleration, and the brain box used to analyze information about engine operating characteristics and, after processing this information, to control the electrically operated injectors.

It is absolutely imperative that no adjustments other than those found in the following pages be performed. The controls for this fuel injection system are extremely sensitive and easily damaged when subject to abuse. Never attempt to test the brain box without proper training and the proper equipment. The dealer is the best place to have any needed work performed.

Whenever a fuel injection component is to be removed or installed, the battery should be disconnected and the ignition turned OFF.

It is not recommended that the inexperienced mechanic work on any portion of the fuel injection system.


1974 Type 4 models equipped with automatic transmission, as well as all 1975-81 Type 1 and Type 2 models, are equipped with an improved system known as the Air Flow Controlled Electronic Fuel Injection System. With this system, some of the electronic sensors and wiring are eliminated, and the control box is smaller. Instead fuel is metered according to intake air flow.

The system consists of the following components:

Intake air sensor-measures intake air volume and temperature and sends voltage signals to the control unit (brain box). It also controls the electric fuel pump by shutting it off when intake air stops. It is located between the air cleaner and the intake air distributor.
Ignition contact breaker points-these are the regular points inside the distributor. When the points open, all four injectors are triggered. The points also send engine speed signals to the control unit. No separate triggering contacts are used.
Throttle valve switch-provides only for full load enrichment. This switch is not adjustable.
Temperature sensor I-senses intake temperature as before. It is now located in the intake air sensor.
Temperature sensor II-senses cylinder head temperature as before.
Control unit (brain box-contains only 80 components compared to the old system's 300.
Pressure regulator-is connected by a vacuum hose to the intake air distributor and is no longer adjustable. It adjusts fuel pressure according to manifold vacuum.
Auxiliary air regulator-provides more air during cold warmup.