INTRODUCTION - DIESEL FUEL INJECTION SYSTEM

1.3 Multijet

FUNCTION

The Magneti Marelli MJD 6F3 Common Rail system is a high pressure electronic injection circuit for fast, direct injection diesel engines.

Its main features are:

• availability of high injection pressure (up to 1400 bar);
• The possibility of modulating pressures from 150 bar up to a maximum service pressure of 1400 bar, regardless of engine rpm and load;
• ability to work at high engine rpms (up to 5000 rpm in full load conditions);
• injection control precision (injection advance and duration);
• reduced fuel consumption;
• reduced emissions.

The main system functions are as follows:

• fuel temperature control;
• engine coolant temperature control;
• control of amount of fuel injected;
• idle speed control;
• fuel cut-off during over-run;
• cylinder balance check when idling;
• control of anti-judder function;
• control of exhaust fumes during acceleration;
• exhaust gas recirculation control (E.G.R.);
• maximum torque limit control;
• maximum speed limit control;
• glowheater plug control;
• control of climate control system activation (where fitted);
• auxiliary fuel pump control;
• cylinder position check for timing;
• main and multiple injection advance control;
• closed cycle injection pressure control;
• electrical balance control;
• IMA injector calibration.
• DPF regeneration control (where present)

The injection system for the version with a Lambda sensor is illustrated in the diagram below.

1. Fuel tank

2. Auxiliary fuel pump

3. Fuel filter

4. Pressure pump

5. Rail

6. Pressure regulator

7. Fuel pressure sensor

8. Injectors

9. Air filter

10. Air flow meter with intake air temperature sensor

11. Compressor

12. Intercooler

13. E.G.R. solenoid

14. Water/exhaust gas heat exchanger for E.G.R. system.

15. E.G.R. diffuser

16. Excess pressure sensor

17. Rpm sensor

18. Timing sensor

19. Water temperature sensor

20. Minimum engine oil pressure switch

21. Heater plugs

22. Heater plugs control unit

23. Fixed geometry turbocharger

24. Waste gate actuator

25. Catalytic converter

26. Lambda sensor (UEGO)

27. Pedal assembly

28. Engine management control unit

The injection system for the version with a DPF is illustrated in the diagram below.

1. Fuel tank

2. Auxiliary fuel pump

3. Fuel filter

4. Pressure pump

5. Rail

6. Pressure regulator

7. Fuel pressure sensor

8. Injectors

9. Air filter

10. Air flow meter with intake air temperature sensor

11. Compressor

12. Intercooler

13. E.G.R. solenoid

14. Water/exhaust gas heat exchanger for E.G.R. system.

15. E.G.R. diffuser

16. Excess pressure sensor

17. Rpm sensor

18. Timing sensor

19. Water temperature sensor

20. Minimum engine oil pressure switch

21. Heater plugs

22. Heater plugs control unit

23. Fixed geometry turbocharger

24. Waste gate actuator

25. Catalytic converter

26. Temperature sensor in DPF intake

27. Particulate filter

28. Pressure sensor for particulate filter

29. Pedal assembly

30. Engine management control unit

31. Waste gate solenoid valve

Introduction

The Common Rail system makes it possible to carry out two pilot injections before T.D.C. with the advantage of distributing the pressure in the combustion chamber more evenly and reducing the combustion noise typical of direct injection engines and up to two injections after the main injection with the advantage of reducing emissions.

The control unit controls the quantity of fuel injected, regulating the line pressure and injection times.

The control unit processes the following information in order to control the quantity of fuel to inject:

• engine rpm;
• coolant temperature;
• turbocharging pressure;
• air temperature (from flow meter);
• intake air quantity;
• battery voltage;
• diesel pressure;
• accelerator pedal position;
• diesel temperature.

Diagram showing information entering/leaving the control unit

1. Auxiliary electric fuel pump

2. Water in diesel sensor

3. Air conditioning compressor (where fitted)

4. E.G.R. solenoid

5. Rev counter

6. Fans

7. Heater plugs control unit

8. Twin track accelerator pedal potentiometer

9. Brake pedal switch - clutch pedal switch

10. Fuel pressure sensor

11. Air flow meter

12. Coolant temperature sensor

13. Fuel temperature sensor

14. Cruise Control (where fitted)

15. Excess pressure sensor

16. Timing sensor

17. Rpm sensor

18. Speedometer

19. Battery

20. Fiat CODE (body computer)

21. Diagnostic socket

22. Pressure regulator

23. Injectors

24. Heater plugs

25. Heater plugs warning light

26. Injection warning light

27. Coolant overheating warning light

28 Water in the fuel warning light

29. Exhaust gas temperature sensor (version with DPF)

30. Differential pressure sensor (version with DPF)

31. Particle filter blocked warning light (version with DPF)

Self-diagnosis

The control unit self-diagnostic system checks the signals coming from the sensors and compares them with the permitted limits.

FAULT SIGNALS DISPLAYED DURING START UP:

• warning light on until engine is started indicates test stage;
• warning light off after engine starting indicates no fault with components that affect the safety of the system;
• warning light on with engine running indicates fault.

FAULT SIGNALS DISPLAYED DURING OPERATION:

• warning light on indicates a fault;
• warning light off indicates no fault with components that affect the safety of the system;

RECOVERY

The control unit defines the recovery settings on each specific occasion according to which components are faulty.

The recovery parameters are managed by non-faulty components.

Fiat CODE recognition

The moment the control unit receives the ignition ON signal it converses with the body computer via the CODE function to obtain the go ahead for starting.

Fuel temperature control

With the temperature of the fuel at 80°C measured by the sensor in the diesel filter, the control unit operates the pressure regulator to reduce the line pressure and, if this is not enough, to also reduce the amount of fuel injected.

Engine coolant temperature control

When the engine coolant temperature is above 105°C, the control unit:

• reduces the quantity of fuel injected (reduces engine power);
• controls the cooling fans;
• switches the coolant temperature warning light on.

Control of the amount of fuel injected

The control unit compares the signals coming from the sensors to the stored values, and:

• controls the pressure regulator;
• varies the "pilot" injection time in the entire rpm range;
• modulates the "main" injection time.

Idle speed check

The control unit processes the signals coming from the various sensors, regulates the quantity of fuel injected and:

• controls the pressure regulator;
• modulates the injector injection times.

Within certain limits the speed is dependent on battery voltage.

Fuel cut-off during over-run

When the accelerator pedal is released, the control unit implements the following strategies:

• Places the injection time at zero;
• Partly varies the injection time for the injectors before the idle speed is reached;
• Controls the fuel pressure regulator.

Idle cylinder balance check.

According to the signals received from the sensors, the control unit controls the idle speed torque:

• modulates the quantity of fuel injected into the individual injectors (injection time).

Anti-judder check

The control unit processes the signals received by the various sensors and corrects the quantity of fuel to inject in order to improve driveability reducing shuddering whilst driving by means of the injector opening time.

Exhaust fume control during acceleration

In order to restrict the fumes during fast transitions, on the basis of the signals received from the accelerator pedal potentiometer, flow meter and the engine speed the control unit limits the amount of fuel to be injected by means of:

• the pressure regulator
• the injector injection time.

Exhaust gas recirculation control (E.G.R.)

In accordance with EURO 3/4 pollution control legislation, on the basis of the engine load and the signal from the accelerator pedal potentiometer, the control unit limits the quantity of intake air, implementing the partial intake of exhaust gases, through:

• adjusting the E.G.R. valve opening.

Maximum torque limit control

The control unit uses mapped values plotted against rpm to calculate the following:

• the torque limit;
• the permitted level of fumes (limit).

It compares these minimum values with other parameters and corrects them:

• coolant temperature;
• engine rpm;
• vehicle speed;
• air temperature,

It also controls the quantity of fuel to be injected (pressure regulator - injectors).

Maximum speed limit control

When the engine speed reaches 5200 rpm, the control unit interrupts the operation of the injectors and the supply pressure is consequently reduced.

Glowheater plug check

The injection control unit, during the following stages:

• start-up;
• post start-up
• times the operation of the glowheater plug control unit on the basis of engine temperature.

Air conditioning system start-up check

The control unit operates the climate control compressor:

• activating/de-activating it when the correct switch is pressed;
• switching it off momentarily (for a few seconds) in the case of strong acceleration or a request for maximum power.

Auxiliary fuel pump check

Irrespective of the rpm, the control unit:

• supplies the auxiliary fuel pump when the key is turned to MAR;
• cuts off the auxiliary pump supply if the engine is not started within a few seconds.

Cylinder position check

During each revolution of the engine the control unit recognises which cylinder is in the combustion stroke and controls the injection sequence within the appropriate cylinder.

Pilot injection and main injection advance check

According to the signals coming from the various sensors, including the absolute pressure sensor built into the control unit itself, the control unit determines the optimum injection point, according to an internal map, designed for driving comfort and also designed to meet EURO 3/4 emission limits.

Injection pressure closed loop check

The control unit controls the regulator to produce optimum line pressure according to engine load, which is determined by processing signals from the various sensors.

Electrical balance check

The control unit modulates idle speed according to the battery voltage and:

• increases the injector injection times;
• modulates the line pressure.

Fan control

Depending on the temperature of the engine coolant and the pressure of the air conditioning system coolant, the control unit controls:

• fan activation at first or second speed.

Fuel cut off function

There is no inertia switch on this vehicle; the fuel cut off function is managed in accordance with the logic described below:

• 1) the Air Bag control unit detects the impact and transmits the activation of the FPS (Fire Prevention System) via the CAN
• 2) after having received the FPS activation signal, the Body Computer Node:
• - activates the hazard signal
• - switches the courtesy light on
• - unlocks the doors
• - transmits that the impact has taken place via the CAN (B and C)
• 3) the instrument panel signals that the fuel cut off function has intervened
• 4) the engine management control unit interrupts the supply of fuel.

Rearming

The following procedure should be carried out using the steering column switch unit lever to restore the correct of the vehicle

• KEY OFF (starting condition)
• KEY ON
• Activation of right indicator
• Deactivation of right indicator
• Activation of left indicator
• Deactivation of left indicator
• Activation of right indicator
• Deactivation of right indicator
• Activation of left indicator
• Deactivation of left indicator
• KEY OFF