E30/E28/E34: Bosch L-Jetronic Fuel Injection System Diagram / Explanation

Two types of fuel injection system are fitted. E21 3er 323i models are equipped with the Bosch K-Jetronic system, whereas E30 3er 320i and 325i models are fitted with the Bosch L-Jetronic system. This article covers L-Jetronic injection for E30 models, also later injected E28 and early E34 5er  For K-Jetronic in E21 models, also injected E12 and early E28 5er, see THIS ARTICLE.

K-Jetronic Operation:
In fuel injection systems of Bosch L-Jetronic type, the volume of air drawn in by the engine is measured.

Each cylinder has its own independent injector.

An additional air slide-valve bypasses the throttle butterfly stub pipe and controls the additional air volume required when the air is still cold. When the engine is warm, idle speed airflow control is by means of another bypass around the throttle butterfly.

Fuel supply and pressure is provided by an electric pump with an inline filter and pressure regulator.

The volume of air drawn into the engine is measured by the air flow meter and this is converted into an electric impulse and transmitted to the control unit. A calculation is made to determine the quantity of fuel to be injected (based upon the engine running speed) into each cylinder.

Automatic cold-start and warm up devices are incorporated into the system with corrections made to the amount of fuel delivered for idle-speed and full-load by contacts in the throttle butterfly switch. When the engine is on the overrun and throttle is closed, due delivery is shut off completely.

The electronic control unit processes information from the various engine sensors and sends an impulse to the electromagnetic fuel injectors, telling them to open for a precisely defined period and deliver a set amount of fuel for each ignition. This is how most modern fuel-injection systems (with the exception of direct-injection systems) work.