Automotive Fuel Injection Systems: KE-Jetronic to MONO-MOTRONIC

KE-Jetronic Fuel Injection System

KE-Jetronic combines K-Jetronic and electronic control. It features an electrohydraulic flow injection system that adapts to engine operating states, enriching or leaning the fuel mixture as needed. Unlike some systems, it does not have a warming phase regulator. Key components include an engine temperature probe, a throttle butterfly switch, and a potentiometer within the flowmeter that determines the position of the plate probe.

L-Jetronic Fuel Injection System

L-Jetronic is a fully electronic system, characterized by intermittent and simultaneous fuel injection. Fuel volume is measured by a paddle-tube flowmeter. Fuel is metered by electromagnetic injectors. This system does not use a fuel distributor/doser. Fuel is sent from the tank, through a filter, and then via an injection pump to a fuel rail. A pressure regulator maintains the correct pressure in the rail. It includes an auxiliary injector for cold starts and a mechanism for extra air during idle. Other components are a throttle butterfly switch, an engine temperature sensor, and a lambda probe for mixture control.

Fuel Pump Technology

The fuel pump is typically a hydrodynamic cell type, often using rollers. Its rotation creates a dragging action, where fuel is drawn from the input and propelled to the output through the impeller's fins and fitted holes.

Fuel Filter Function

The fuel filter uses porous paper to retain impurities and a sieve to capture particles, ensuring clean fuel delivery.

Fuel Pressure Regulator

The fuel pressure regulator maintains the fuel rail pressure, typically around 3 bar, by returning surplus fuel to the tank. It is a membrane-type component, consisting of a metallic body formed into two chambers separated by a membrane. A valve is attached to the bottom of the membrane, which is influenced by spring pressure and vacuum lines.

Electromagnetic Fuel Injectors

Fuel injectors are electromagnetic components commanded by the Engine Control Unit (ECU). They spray fuel into each intake manifold runner, just before the admission valve. These injectors atomize the fuel; they do not dose it by opening pressure. The opening pressure is typically around 3.5 bar, and they are inserted into the manifold under pressure.

Air Flow Meter (Paddle Type)

The paddle-type air flow meter is located between the air filter and the throttle body. Its operation is based on measuring the force exerted by the incoming air stream on a movable paddle. As air flows through the meter, the paddle shifts, and a potentiometer generates a voltage signal corresponding to the paddle's position. This signal indicates the air flow. The design often includes a compensation butterfly to mitigate pressure waves created in the intake manifold, which could otherwise affect the probe's position. The paddle-probe's position, indicated by the potentiometer's voltage (typically fed 5V), is crucial for correcting the injected fuel volume.

LH-Jetronic Fuel Injection System

LH-Jetronic utilizes a hot-wire type air flow meter. This component consists of a ring, a heated wire, and a resistance. It operates on the principle of maintaining a constant temperature for the hot wire. The wire is part of a bridge circuit; as air flows past it, the heating current varies to maintain its temperature, and this change in current is measured to determine air mass.

MONO-MOTRONIC Single Point Injection

MONO-MOTRONIC is a single-point injection system that combines both fuel injection and ignition control. It features a central injection unit, often referred to as the throttle body, which houses a pressure regulator with fuel return to the tank and the throttle butterfly valve. A unique electro-injector supplies fuel into the intake manifold, which then distributes it to the cylinders. The system includes an idle speed regulator, typically a stepper motor, an air temperature probe, and a throttle position potentiometer. Engine speed and timing are determined by impulses from a sensor located in the distributor. A lambda probe is also present to correct the air-fuel mixture based on oxygen content in the exhaust. The fuel pump for this system is submerged within the fuel tank.