2888229 - 1056B multi-point injection system (mpi)

The Marelli IAW 49F system belongs to the category of systems integrated with:

• inductive discharge digital electronic ignition
• distributorless
• sequential, phased electronic injection (1-3-4-2).

1, Safety and ventilation valve 2, Fuel tank 3, Electric fuel pump 4, Idle speed actuator 5, Radiator fan high and low speed relay feeds 6, Battery 7, Ignition switch 8, Injection system relay 9, Fiat CODE control unit 10, Inertia switch 11, Vehicle speed sensor 12, Diagnostic socket 13, Rev counter 14, Injection system failure warning light 15, Fuses protecting injection/ignition system 16, General protective fuse box 17, Butterfly valve position sensor 18, Fuel supply manifold 19, Injectors 20, Air filter 21, Spark plugs 22, Ignition coils 23, Engine coolant temperature gauge 24, Air temperature and pressure sensor 25, Rpm and T.D.C. sensor 26, Detonation sensor 27, Coolant temperature sensor 28, Fuel vapour solenoid valve 29, Active charcoal filter 30, Climate control compressor 31, Lambda sensor 32, Catalytic silencer 33, Injection/ignition control unit 34, Multi-purpose valve 35, Engine coolant overheating warning light 36, Climate control compressor relay 37, Climate control system relay

OPERATION OF THE FUEL INJECTION-IGNITION

During idling, the control unit checks:

• the ignition instant
• air flow

with the benefit of maintaining correct operation of the engine when the environmental parameters and the applied loads vary.The control unit controls and manages fuel injection so that the stoichiometric ratio (air/fuel) is always at the optimum value.

The system's functions are basically as follows:

• system self-adaptation
• autodiagnosis
• recognition of FIAT CODE
• control of cold starting
• check on combustion - Lambda probe
• control of detonation
• control of enrichment during acceleration
• fuel cut-off during overrunning
• fuel vapour recovery
• limitation of maximum rpm
• check on fuel-electric fuel pump supply
• connection to the climate control system
• recognition of cylinder position
• regulation of fuel injection times
• adjustment of ignition advance values
• check and management of idle speed
• check on electric cooling fan

Injection system

The essential conditions that must always be met in the preparation of the air-fuel mixture for the correct operation of controlled-ignition engines are mainly:

• the 'metering' (air/fuel ratio) must constantly be kept as close as possible to the stoichiometric ratio, so as to ensure the necessary rapidity of combustion, avoiding unnecessary fuel consumption
• the 'homogeneity' of the mixture, consisting of petrol vapours, diffused as finely and evenly as possible in the air.

The injection/ignition system uses an indirect measuring system known as the 'SPEED DENSITY LAMBDA' type. In other words the angular rotation speed, density of the intake air and control of the mixture strength.In practice the system uses data on the ENGINE SPEED (rpm) and 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 each engine cycle depends not only on the density of the intake air, but also on the unit displacement and the volumetric efficiency.The density of the air refers to that of the air drawn in by the engine and calculated according to the absolute pressure and the temperature, both detected in the inlet manifold.Volumetric efficiency refers to the parameter relating to the coefficient for filling the cylinders measured on the basis of experimental tests carried out on the engine throughout the entire operating range and then stored in the electronic control unit memory.Having established the quantity of intake air, the system has to provide the quantity of fuel according to the desired mixture strength.The end of injection pulse or supply timing is contained in a map stored in the control unit memory and varies according to the engine speed and the pressure in the inlet manifold. In practice, it involves processing which the electronic control unit carries out to command the sequential, phased opening of the four injectors, one per cylinder, for the length of time strictly necessary to form the air/petrol mixture which is closest to the stoichiometric ratio.The fuel is injected directly into the manifold near the inlet valve at a pressure of around 3 bar.Whilst the speed (rpm) and the density of the air (pressure and temperature) are used to measure the quantity of intake air, which when established allows the quantity of fuel to be metered according to the desired mixture strength, the other sensors in the system (coolant temperature, butterfly valve position, battery voltage, etc.) allow the electronic control unit to correct the basic strategy for all engine operating conditions.It is vital for the air/fuel ratio to be around the stoichiometric value for the correct and prolonged operation of the catalytic silencer and for the reduction of pollutant emissions.

Ignition system

The ignition is the inductive discharge type, i.e. without a high tension distributor, with power modules located in the electronic injection/ignition control unit.The system has two high tension twin outlet coils joined in a single container and connected directly to the spark plugs.The primary winding for each coil is connected to the power relay (thereby receiving the battery voltage) and to the pins for the electronic control unit for connection to earth.

After the starting stage, the electronic unit manages the basic advance taken from a special map according to the:

• engine rotation speed
• absolute pressure value (mmHg) measured in the inlet manifold.

This advance value is corrected according to the temperature of the engine coolant and the intake air.The spark plugs for cylinder 1-4 and 2-3 are connected directly (two at a time) by means of high tension leads to the terminals of the coil secondary winding and their connection is in series because the cylinder head joins them. This solution is also known as the 'lost spark' becuse the energy accumulated by the coil is almost exclusively discharged at the electrodes for the spark plug of the cylinder under compression allowing the ignition of the mixture. The other spark is obviously not used, as no mixture is found in the cylinder to ignite, only exhaust gas.

OPERATION

Diagram of input/output information from the control unit

- 1, Electronic control unit 2, Speedometer sensor 3, Fiat CODE control unit 4, Engine idle speed actuator 5, Fuel injectors 6, Fuel vapour solenoid valve 7, Diagnostic socket 8, Spark plugs 9, Ignition coils 10, Engine coolant overheating warning light 11, Injection failure warning light 12, Climate control system 13, Engine coolant temperature sensor 14, Intake air temperature and pressure sensor 15, Butterfly valve position sensor 16, Detonation sensor 17, Rpm and TDC sensor 18, Ignition switch 19, Lambda sensor 20, Electric fuel pump 21, Radiator fan high and low speed relay feeds 22, Speedometer / milometer

OPERATING LOGICS

Self-adaptation of the system

The control unit has a self-adaption function which recognizes changes in the engine which occur as a result of bedding-in and ageing processes of both components and the engine itself. These changes are stored in the form of modifications to the basic mapping, and their purpose is to adapt the operation of the system to the gradual alterations in the engine and components compared with their characteristics when new. This self-adaptation function also makes it possible to even out inevitable differences (due to production tolerances) in any replaced components.From the exhaust gas analysis, the control unit changes the basic mapping in relation to the original characteristics of the new engineThe self-adaptation parameters are not cancelled if the battery is disconnected.

Self-diagnosis

The system has an autodiagnostic function which recognizes, memorizes and signals any failures.If a fault is detected at the sensors or actuators, the signal reconstruction strategies (recovery) are immediatedly activated to guarantee the operation of the engine at an acceptable level without adverse effects. The vehicle can therefore be driven to a service centre for repair.

Recognition of fiat code

When the control unit receives the ignition 'ON' signal, it dialogues with the Fiat CODE control unit to obtain starting enablement.Communication takes place via the dedicated bidirectional serial diagnostic line which connects the two control units.

Starting and post-starting

During starting it is not possible to instantly recognize the engine timing and consequently it is not possible to implement the timed injection for the first injection for each cylinder.When the engine is first running an initial simultaneous (full-group) injection is carried out because the considerable fluctuations in the rotation speed do not allow the correct calculation of the injection stage; it is only later that the injection becomes phased. There is no timing sensor and the correct operation of the sequential-phased system is ensured by the 'software timing sensor' function.

This term refers to a collection of processes which the engine control unit carries out to reconstruct the missing signal and ensure the correct 'square signal':

• memorizing the last cylinder in the inlet stroke when the engine is switched off;
• confirming the correct 'timing' within 5 seconds of starting and periodically during normal engine operation, by occasionally suppressing the petrol at one injector only.

The 'basic' injection time is increased by a multiplication coefficient for the entire time the engine is driven by the starter motor.After starting, the coefficient is gradually reduced until it disappears within a certain period; the lower the engine temperature, the longer this period.

Operation when cold

Under these circumstances there is a natural weakening of the mixture because of the poor turbulence of the fuel particles at low temperatures, reduced evaporation and condensation on the inner walls of the inlet manifold, all of which is exacerbated by the increased viscosity of the lubricant oil which, as is well known, increases the rolling torque of the engine mechanical components at low temperatures.The electronic control unit recognizes this condition on the basis of the coolant temperature signal, increasing the basic injection time.Whilst the engine is warming up, the electronic control unit also operates the stepping motor which determines the quantity of air needed to ensure that the engine does not cut out.

Operation in full load conditions

Operation in full load conditions is detected, by the control unit, through the values supplied by the butterfly position and absolute pressure sensors.In full load conditions, the basic injection time must be increased to obtain the maximum power supplied by the engine.

Operation in deceleration conditions

During this stage the engine has two strategies:

• A negative, transitory strategy to keep the quantity of fuel supplied to the engine at the stoichiometric value (less pollution). This stage is recognized by the control unit when the butterfly potentiometer signal goes from a high voltage reading to a lower one.
• A soft accompaniment strategy at the lower speed (dash-pot) to lessen the variation in the torque supplied (reduced engine braking).

The atmospheric pressure varies according to the altitude creating a variation in the volumetric efficiency which requires the correction of the basic mixture strength (injection time). The correction of the injection time depends on the variation in altitude and is automatically updated by the electronic control unit each time the engine is switched off and in certain butterfly position and rpm conditions (typically at low speeds and with the butterfly wide open) (dynamic adjustment of barometric correction).The cut-off strategy is implemented when the control unit recognizes the butterfly valve in the idle position (butterfly potentiometer signal) and the engine speed exceeds 1350 rpm. The control unit only enables the cut-off when the engine temperature exceeds 0° C.The recognition of the butterfly valve in a non closed position or the engine speed below 1270 rpm enables the supply to the engine.For very high speeds the cut-off is implemented even when the butterfly is not completely closed, but when the pressure in the inlet manifold is particularly low (partial cut-off).

Operation in acceleration conditions

During this stage, the control unit increases the quantity of fuel requested by the engine as appropriate (to achieve maximum torque) according to the signals coming from the following components:

• butterfly potentiometer;
• Rpm and T.D.C. sensor

The 'basic' injection time is multiplied by a coefficient which depends on the temperature of the engine coolant, the opening speed of the accelerator butterfly and the increase in pressure in the inlet manifold. If the sharp variation in the injection time is calculated when the injector is already closed, the control unit reopens the injector (extra pulse) in order to compensate the mixture strength extremely quickly; the subsequent injections are already increased on the basis of the coefficients mentioned previously.

Protection against excess rpm

When the engine rotation speed exceeds 6700 rpm for more than 10 seconds or reaches the 'limit' of 6900 rpm, set by the manufacturer, the engine finds itself operating in 'critical' conditions.When the electronic control unit recognizes that the above speed has been exceeded, it prevents the operation of the injectors.When the rotation speed returns to a non critical value, the operation is resumed.

Electric fuel pump operation

The electric fuel pump is controlled by the engine control unit by means of a relay.

The pump cuts out:

• if the engine speed goes below about 50 rpm
• after a certain period (about 5 seconds) with the ignition switch in the ON position without the engine being started up (timed go ahead)
• if the inertia switch is operated.

Injector operation

The operation of the injectors is the sequential, phased type. However, during starting the injectors are operated once in parallel (full-group).The timing of the injector operation varies according to the engine speed and pressure of the inlet air in order to improve the filling of the cylinders with advantages in terms of consumption, driveability and pollution.

Control of knock

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