Beginning in 1982 for the Spider, and 1981 for the GTV6, Alfa went to Bosch fuel injection. The heart of this system is the airflow meter, which measures the amount of air being required by the engine. Hence the name L-Jetronic; the “L" stands for “luft", the German word for air. This has proven to be a supremely reliable and efficient system. When failures do arise, they are generally easy to diagnose. Here is a brief overview of how the system operates:

Gasoline is supplied to the injectors by an electric pump. Two pumps are used on Spiders, one submerged in the tank, and one under the car in front of the tank. The pumps are controlled by the combi-relay. This relay is in turn switched on and off by a microswitch attached to the air flap inside of the airflow meter. At the end of the injector rail is a fuel pressure regulator that maintains constant fuel pressure. The regulator detects engine load by sensing manifold vacuum, and returns the unused fuel back to the tank.

The injectors themselves are simply solenoid valves aimed at each intake port.

They're either on or off, so the amount of fuel injected is determined by the length of time they're energized (called the "pulse width"; a typical range is 1/7,000th to 1/1,000th of a second).

The electronic control unit provides the high-speed ground that completes the circuit to the injectors. It determines the span of open time that will result in the ideal mixture for the particular conditions, based on the input from various sensors. The most important of these is the air flow meter, which is mounted between the air filter and the throttle plate. Info on operating temperature, rpm and exhaust gas oxygen content is also critical for accurate fuel metering, and is provided by the temperature sensor, the ignition pickup, and the oxygen sensor, respectively.

An extra injector, the cold start valve, provides extra fuel into the manifold for starting. It is controlled by the thermo-time switch, which senses coolant temperature. The auxiliary air valve admits extra air during warm-up to provide decent idling.

- back to Tips and Techniques -