Fuel system management strategies

The Fiat Bravo and Brava 1.9 JTD are equipped with a 4 cylinder in line 1920 cc turbodiesel engine with two valves per cylinder, a counter-balance shaft, an overhead camshaft, supercharged by a turbocharger with an intercooler and with electronic fuel injection.

The fuel system ensures the correct operation of the engine and can be divided into the following circuits:

• fuel supply circuit with common rail type injection;
• air supply circuit;
• exhaust circuit;
• oil vapour recirculation circuit from the crankcase;
• exhaust gas recirculation circuit (EGR).

The optimum operation of the various fuel system "circuits" is achieved through an electronic control system managed by a special control unit.

The main feature of the fuel system is the common rail type injection of the fuel. This is a high pressure electronic injection system for direct injection fast diesel engines.

The main features of the common rail system are:

• availability of high injection pressures (up to 1350 bar);
• possibility of modulating these pressures (from a minimum of 150 bar up to a maximum of 1350 bar) indepedent of the engine rotation speed and load;
• capacity to operate at high engine speeds (up to 6000 rpm);
• precision injection operation (advance and duration of the injection);
• reduction in fuel consumption;
• reduction in emissions.

FUEL SYSTEM MANAGEMENT STRATEGIES

There is a management programme (software) in the control unit memory which consists of a series of strategies, each of which manages a precise system control function.

By using information supplied by the various sensors (input), each strategy processes a series of parameters, using maps stored in special areas of the control unit memory and then operates the system actuators (output) which are the devices which allow the operation of the engine.

The main aim of the management strategies is to determine the exact quantity of fuel which should be injected into the cylinders at one time (injection advance) and the pressure to achieve the best engine behaviour in terms of power, consumption, fumes, emissions and driveability.

The main system management strategies are, basically, as follows:

• control of quantity of fuel injected;
• control of injection advance;
• control of injection pressure;
• control of auxiliary electric fuel pump;
• control of injection during deceleration (Cut-off);
• control of idle speed;
• control of maximum speed restriction;
• control of maximum torque restriction;
• control of fuel temperature;
• control of engine coolant temperature;
• control of heater plugs;
• control of exhaust fumes;
• control of exhaust gas recirculation (EGR);
• control of engagement of climate control system;
• control of engine immobilizer function (Fiat CODE);
• autodiagnosis.