199004991 - INTRODUCTION - PETROL FUEL INJECTION SYSTEM

SPECIFICATIONS

GENERAL SPECIFICATIONS

The Bosch Motronic ME7.9.10 system with a motorized throttle belongs to the category of ignition systems which have built-in, phased, sequential electronic injection.The control unit electronically manages the air flow rate at the rotation speed set by the electronic throttle, regulates the fuel injection so that the (air/fuel) ratio is always within optimum values, calculating the moment of ignition, in order to allow the smooth operation of the engine when the environmental parameters and loads applied vary.The ignition system is static advance with a single coil with three outlets. The power modules are housed inside the control unit.The self-adaptive engine management system can recognise the changes that take place in the engine. It compensates for them using the self-adaptive functions that correct the fuel mixture and air flow plans mapped in the control unit.There are two adaptive functions, in particular, for the fuel mixture plan, depending on whether the evaporation control solenoid valve is open or closed, plus an idle adaptation plan: the latter is capable of compensating effectively for any air seepage.The continuous self-adaptation of the fuel mixture plan makes it possible to ensure the correct amount of fuel in all temperature and altitude conditions.As a result of this, after every intervention it is necessary to drive the vehicle for at least 15 minutes in various operating conditions in order for any changes that have taken place in the system to be memorised in the control unit and to end the adaptation.

The main system functions are as follows:

  • injection time adjustment;
  • ignition advance adjustment;
  • cold starting check;
  • enrichment check during acceleration;
  • fuel cut-off during over-run;
  • idle speed management (also dependent on battery voltage);
  • restriction of the maximum engine speed;
  • combustion control with Lambda sensor;
  • petrol vapour recovery;
  • fan control;
  • climate control system engagement/disengagement;
  • self-diagnosis;
  • slider on-off control;
  • continuous variable valve timing control;
  • calculation of the vehicle speed;
  • automatic management of engine starting.

There is also a special function that manages the connection with the body computer via a two-way signal for the CAN line. This includes:

  • engine temperature for instrument panel (output);
  • battery voltage (output);
  • engine rpm (output) for instrument panel;
  • engine overheating warning light for instrument panel (output);
  • engine oil pressure warning light for instrument panel (output);
  • vehicle speed (output) + mileometer (input/output);
  • Fiat code anti-theft device (input/output);
  • key status;
  • consumption signal (output) for trip computer;
  • fuel level signal (input)

Injection system

The essential conditions to be met by the air-fuel mixture for the efficient operation of engines with controlled ignition systems are mainly as follows:

  • the metering (air/fuel ratio) must be kept as close as possible to the stoichiometric value in order to ensure that combustion is as fast as possible, thus avoiding fuel wastage
  • the homogenity of the mixture, composed of fuel vapour, is diffused in the air as finely and uniformly as possible to ensure good condition and efficiency of catalytic converter timing.
The injection/ignition system uses an indirect measuring system known as "SPEED DENSITY-LAMBDA".In other words, angular rotation speed, intake air density and control of mixture strength (feedback control).In practice, the system uses the ENGINE SPEED data (rpm) and the AIR DENSITY (pressure and temperature) to measure the quantity of air drawn in by the engine.The quantity of air drawn in by each cylinder, for every engine cycle, also depends on the unit capacity, the volumetric efficiency, and the turbocharging, as well as on the density of the intake air.The density of the air refers to the air drawn in by the engine and is calculated according to the absolute pressure and temperature, both measured in the intake manifold.
With the engine management system, based on management of the drive torque, the amount of fuel is calculated by taking into account the factors that determine an increase or decrease.
Volumetric efficiency is the parameter that measures the cylinder filling coefficient, measured on the basis of experiments conducted on the engine for the entire operating range and then stored in the electronic control unit memory.Having established the quantity of intake air, the system must provide the amount of fuel dictated by the desired mixture strength.The end of injection impulse or delivery timing is stored in a map in the control unit memory and varies according to the engine speed and the pressure in the intake manifold.In practice, it involves processing carried out by the electronic control unit to manage the timed, sequential opening of the four injectors, one per cylinder, for the length of time strictly necessary to make the air/petrol mixture as close as possible to the stoichiometric ratio.The fuel is injected directly into the manifold, near the inlet valves, at a pressure of around 3.5 bar.The speed (rpm) and the density of the air (pressure and temperature) are used for measuring the quantity of intake air which, when established, is used for metering the amount of fuel needed for the desired mixture strength.The other sensors in the system (coolant temperature, throttle valve position, battery voltage, etc.) allow the electronic control unit to correct the basic strategy for all the engine operating conditions.

Ignition system

The ignition circuit is solid-state inductive discharge type, i.e. without an HT distributor, with power modules located inside the injection-ignition electronic control unit.The primary winding of each coil is connected to the power relay (thereby receiving battery voltage) and to the pins of the electronic control unit for earth connection.

After the starting stage, the electronic unit manages the basic advance taken from special maps in accordance with:

  • engine rpm
  • absolute pressure value (mmHg) measured in the intake manifold;
  • engine temperature.
Ignition advance is corrected by torque management strategy, as in the case of fuel injection.The spark plugs for the cylinders are connected directly to the coil secondary winding terminals (one per spark plug).

OPERATION

Diagram showing information entering/leaving the control unit

The information entering/leaving the control unit is illustrated in the diagram below.
1, Engine management control unit with air pressure sensor2, Battery3, Ignition switch4, Engine control system relay5, Cruise Control lever6, Linear pressure sensor7 - Brake pedal and clutch pedal switches8, Lambda sensor upstream and downstream of the converter9, Timing sensor10, Engine coolant temperature sensor11, Knock sensor12, Turbo pressure sensor13, Engine rpm and TDC sensor14, Intake air temperature and pressure sensor15, Electric fuel pump relay16, Fuel pump17, Radiator fan relay18, Radiator fan19, Compressor engagement relay20, Air conditioning compressor21, Injection system fault warning light22, Fuel vapour solenoid23, Waste gate solenoid24, Shut-off solenoid25, Injectors26, Ignition coils27, Throttle control actuator and throttle position sensor28, Body computer (connected to C-CAN)29, Diagnostic equipment connection (via CAN)30, Rev counter (via CAN)31, Speedometer (via CAN and ABS control unit)32, Power steering button (via CAN)33, Switch for oil pressure warning light34, Accelerator pedal sensor

SELF-LEARNING

The control unit implements the self-learning logic under the following conditions:

  • removing-refitting or replacement of the injection control unit
  • removing-refitting or replacement of the throttle body
The values stored by the control unit are retained when the battery is disconnected.

SYSTEM SELF-ADJUSTMENT

The control unit is equipped with a self-adjustment function that is designed to recognize the changes that take place in the engine due to the processes of bedding in and ageing of both the components and the engine itself in time.These changes are memorised in the form of modifications to the basic map and are designed to adapt the operation of the system to the gradual alterations in the engine and the components, compared with when they were new.This self-adjustment function also makes it possible to compensate for the inevitable differences in any replacement components (owing to production tolerances).On the basis of exhaust gas analysis, the control unit modifies the basic map in relation to engine specifications when new.The following self-adaption strategies are provided in the control unit:- mixture strength control multiplied coefficient, takes into account the mixture strength leaning to the probe drift, injectors, air chamber and continually updates while the engine is operating.- mixture strength control additive coefficient, corrects injector leaks and updates when idling.The self-adjustment parameters are not deleted when the battery is disconnected.

AUTODIAGNOSIS AND RECOVERY

The control unit auto-diagnostic system checks that the system is working properly and signals any irregularities by means of an MIL warning light in the instrument panel with a standardised icon and colour, as laid down by European regulations.This warning light indicates engine management faults and also faults detected by EOBD diagnostic strategies.The MIL warning light operating logic is as follows.The warning light comes on with the ignition on and remains on until the engine is started up; the control unit autodiagnostic system checks the signals coming from the sensors and compares them with the permitted data limits.

Fault indication during start up:

  • the failure of the warning light to go out when the engine has been started indicates that there is an error memorized in the control unit.

Fault indication during operation:

  • the warning light comes on in flashing mode to indicate possible catalytic converter damage due to misfiring.
  • the warning light comes on in constant mode to indicate the presence of engine management or EOBD diagnostic errors.
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.The recovery strategies that can be activated from the control unit are:- limp home following throttle body error- limp home following accelerator pedal error- turbocharging; the throttle is closed when there is a rise in the turbocharging pressure during the transient stages of acceleration with the target pressure and the measured pressure differential greater than 200 mbar, while a turbocharging pressure limit is activated if there is an error with the accelerator pedal or throttle actuator.European regulations require the EOBD system to use the following strategies relating to the engine subsystems that have a direct impact on emissions:- fuel supply system (fuel system diagnosis), to detect any malfunctions on the fuel line.- Lambda diagnosis to detect operating errors in the probe upstream of the converter.- converter diagnosis to detect deterioration via indirect measuring of the oxygen storage capacity.- diagnosis relating to irregular ignition (misfire diagnosis) that stops the converter functioning correctly, potentially causing irreversible damage.

SYSTEM CONTROLS AND MANAGEMENT

Fiat code recognition

The moment the control unit receives the MAR signal, it converses with the body computer to obtain the go-ahead for starting.
The starter motor is controlled directly by the key and not by the control unit.
The communication takes place through the CAN line.
As in the last example, the W recovery line is not used again.

Cold starting check

The following occurs in cold starting conditions:

  • a natural weakening of the mixture (which causes poor turbulence of the fuel particles at low temperatures)
  • reduced evaporation of the fuel
  • fuel condensation on inner walls of the intake manifold
  • higher lubrication oil viscosity.

The electronic control unit detects this condition and corrects the injection time on the basis of:

  • coolant temperature
  • intake air temperature
  • battery voltage
  • engine rpm.
The ignition advance is determined solely on the basis of rpm and coolant temperature.Below a set calibration (from approx. 15°C to approx. 25 °C) the ''multispark'' ignition mode is enabledThis strategy, achieved by controlling the coils to obtain a quick series of sparks, facilitates combustion of the mixture.The rotation speed decreases proportionally as the engine temperature increases, until the nominal value is reached when the engine has warmed up.

Combustion - lambda sensor check

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