fiatFI_may2002.pdf

a mirafiori.com guide

Bosch L-Jetronic Fuel Injection Guide

FIAT Fuel Injected Engines " F irst Edition - July 2004

Brad Artigue

Contents

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

How L-Jetronic Works

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.

Bosch L-Jetronic System

on the FIAT 2000cc Engine

The fuel injection computer is tasked with making decisions based on these inputs. It is programmed to

adjust the entire system for external and internal conditions. For example, if it is a cold day and your

engine is cold, the water temperature sensor will tell the computer the engine is cold. The computer will

adjust the air/fuel ratio as necessary to compensate for the cold exterior air. It also receives an input from

the thermo-time switch, a temperature sensor that turns on the cold start valve, providing an even richer

mixture while the engine is cold.

At this point you should have a general understanding of how electronic fuel injection works. The

following sections will describe the fuel injection components as used on FIAT vehicles in some detail.

Sensors

The Bosch L-Jetronic system has a variety of sensors designed to signal the ECU (electronic control unit)

throughout engine operation. There are two water temperature sensors, one throttle position sensor, one

exhaust sensor, and one air flow meter that all signal the ECU and must be operating correctly in order

for your fuel injection system to remain efficient.

Thermo-Time Switch

The thermo-time switch is located directly under the intake manifold

between the #2 and #3 cylinder. It is screwed into the water

passage that runs under the manifold and detects engine

temperatures. When the engine is very cold the thermo-time switch

turns on the cold start injector for a certain amount of time (enough

to get the engine barely warm) then shuts it back off.

Failure of this switch will cause some difficulty in starting or a rich

condition when driving at normal temperatures.

Throttle Position Sensor

The throttle position sensor is located on the intake manifold on the

opposite side of the big air hose from the throttle return spring. It

rotates (internally) against a ceramic plate, the resistance of which is

sent back to the ECU. The ECU uses this information to direct more

(or less) fuel into the engine or shut off the injectors (during

deceleration).

Failure or miscalibration of this sensor will cause the engine to run

poorly at some or all speeds and will cause light puffing "backfires"

while decelerating.

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