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Bosch L-Jetronic Fuel Injection Guide
FIAT Fuel Injected Engines " F irst Edition - July 2004
Brad Artigue
Contents
3
5
7
9
11
Regulators, Injectors, and Pumps
Double Relay and Electronic Control Unit
How L-Jetronic Works
Mechanical Components
The Fuel Injection Tune Up
Regulator, Injector, and Pump Testing
Sensors
Electrical Diagram
Performance Considerations
Lambda
Sensor Testing
12
13
14
17
18
19
Copyright (c) 2004 Bradley J. Artigue
Images Scanned with Permission
This document is freely distributable in its original form.
How L-Jetronic Works
In 1980 FIAT introduced a Bosch multiport fuel injection system in its vehicles. Introduced first on
California-bound vehicles and, by 1981, on all U.S. vehicles, the Bosch system improved the
performance, efficiency, reliability, and quality of engine operations. Solely responsible for a 23
horsepower increase on the 2 liter engines, this system, known as Bosch L-Jetronic, was popular not only
on FIATs but on nearly every European car produced in the 1980's.
The L-Jetronic was the first mass-produced, fully electronic fuel injection system. Prior to L-Jetronic,
mechanical fuel injection systems had proven that directly injecting atomized fuel into the cylinder
resulted in better engine operation. Combining this direct injection theory with electronic sensors, valves,
and meters - all controlled by a central computer - resulted in better operation than before.
The basic operation is straightforward. An engine is basically an air pump, drawing mixed fuel and air
into the intake manifold, compressing it (followed by a spark-triggered explosion), and expelling it
through the exhaust manifold. In a fuel injection system the entire operation is based on the amount of
air entering the system. The engine pulls air through an air filter and into an air flow meter. The air flow
meter measures the amount of air entering the system. Once measured, the air flows into a large hose
that is connected to the intake manifold (a plenum). The intake manifold has a throttle plate that is
connected to the driver's foot (the accelerator pedal). The position of this plate determines how much air
is drawn into the manifold. Air is then passed into one of four barrels connecting the manifold to the
cylinder head. A fuel injector is positioned each barrel and, as air passes through, fuel is sprayed for a
specific amount of time into the air stream.
Bosch L-Jetronic System
on the FIAT 1500cc Engine
This basic operation is achievable without an electronic fuel injection system. What an electronic system offers is precise control over fuel delivery and air flow. Utilizing sensors that determine air and engine temperature, throttle position, exhaust gas content, and engine speed, an electronic system can precisely meter the input of air and fuel. The result is a smooth, efficient engine. Electronic fuel injection is a system of electronic inputs and mechanical actions. On the FIAT system, the electronic inputs are water temperature, air temperature, engine speed, exhaust gases, and throttle position. Expanding upon the basic fuel injection operation described on the previous page, these inputs are gathered by sensors located in your engine compartment. They are very easy to locate - the water temperature sensors are located in the coolant "T" bolted to and in front of the cylinder head and underneath the intake manifold. The air temperature sensor is integrated into the air flow meter. The engine speed sensor is read from your coil and throttle position by a smallish black box (roughly triangular in shape) attached to the intake manifold and opposite your throttle spring. Finally, the exhaust sensor (or oxygen sensor) is located in your exhaust system, just below the collection point for all four cylinders. These inputs connect to your fuel injection computer, which is located in the interior of the car. As your car operates these sensors send continuous signals to the computer.
Get the file Download here
This basic operation is achievable without an electronic fuel injection system. What an electronic system offers is precise control over fuel delivery and air flow. Utilizing sensors that determine air and engine temperature, throttle position, exhaust gas content, and engine speed, an electronic system can precisely meter the input of air and fuel. The result is a smooth, efficient engine. Electronic fuel injection is a system of electronic inputs and mechanical actions. On the FIAT system, the electronic inputs are water temperature, air temperature, engine speed, exhaust gases, and throttle position. Expanding upon the basic fuel injection operation described on the previous page, these inputs are gathered by sensors located in your engine compartment. They are very easy to locate - the water temperature sensors are located in the coolant "T" bolted to and in front of the cylinder head and underneath the intake manifold. The air temperature sensor is integrated into the air flow meter. The engine speed sensor is read from your coil and throttle position by a smallish black box (roughly triangular in shape) attached to the intake manifold and opposite your throttle spring. Finally, the exhaust sensor (or oxygen sensor) is located in your exhaust system, just below the collection point for all four cylinders. These inputs connect to your fuel injection computer, which is located in the interior of the car. As your car operates these sensors send continuous signals to the computer.
Get the file Download here
