Ford Workshop Service and Repair Manuals

PCM

A Bosch generation MED 7.8.1 PCM is used for the engine management.

The additional functions for the direct petrol injection require high processing power from the microprocessor (40 MHz clock frequency).

If the PCM needs to be replaced then the vehicle-specific data records need to be called up with the aid of WDS.

Communications between the PCM and other control units (for example the Electronic Stability Program (ESP)) and the diagnosis of the system take place on the CAN databus.

Each of the units connected to the bus makes its data available on the databus, providing all participants with equal access to the information.

Sensors

CKP sensor

The CKP sensor is mounted on the cover of the timing chain housing, to one side of the crankshaft vibration damper.

Precise timing for the start of injection is an essential requirement for direct petrol injection. The required degree of accuracy can no longer be achieved with a tooth pitch of 36-1.

The tooth pitch of 60-2 on the vibration damper enables a high resolution (due to the greater number of amplitudes per revolution) and therefore guarantees an optimum degree of precision for the determination of the injection timing.

In the event of signal failure the engine will stall or fail to start. In the event of a malfunction a resistance measurement can be performed on the CKP sensor.

Note: A new special tool is used to align the bracket of the CKP sensor:

• Adjusting Tool 303-1060

CMP sensor

As on an engine with direct petrol injection the fuel is injected directly into the combustion chamber, the CMP signal is an essential requirement, because no combustion can take place if the injection is out by one revolution of the crankshaft.

In this case the injected fuel could enter the catalytic converter via the exhaust valve and cause damage to the catalytic converter.

Therefore, once the engine is started the PCM must actuate the injector and the ignition coil of the cylinders which are in the compression or power stroke.

The CMP sensor here is a Hall sensor and is supplied with a reference voltage of 5 V.

In the event of signal failure while the engine is running the injection system continues to inject sequentially until the engine is switched off. It is then not possible to restart the engine

Pressure sensor for the brake booster

A pressure sensor is located on the brake booster which measures the pressure in the brake booster.

When the brakes are operated in homogeneous mode, a very low engine torque and therefore a small intake manifold vacuum are requested via the accelerator pedal. This vacuum is normally sufficient to provide the required boost for braking.

In stratified mode the engine is operated for the most part with little throttle restriction (low intake manifold vacuum), as a result of which the vacuum in the brake booster can drop below a critical level.

If the pressure in the brake booster drops to a certain value, then this is detected by the pressure sensor for the brake booster and signalled to the PCM.

The brake booster control then requests sufficient vacuum via the intake manifold pressure coordination system.

In response to this the throttle valve is closed as far as necessary, whereby enough air is allowed to enter to enable combustion to still take place.

If the permissible closing of the throttle valve in stratified mode is not sufficient then the system requests homogeneous mode.

A reference voltage of 5 V is applied to the pressure sensor for the brake booster.

In the event of signal failure it is no longer possible to operate the engine without throttle restriction, which means that the engine is then only run in homogeneous mode.

Fuel pressure sensor

The fuel pressure sensor is used to measure the fuel pressure in the fuel rail. This value is taken as the actual value for the pressure control in the fuel rail.

In terms of the power output of the engine and the emissions of harmful pollutants, it is of key importance that the pressure in the fuel rail accurately matches the set value.

The fuel pressure is regulated by the fuel metering valve in a closed loop circuit.

The measurement is performed with a thin steel diaphragm, to which stretch resistances are attached.

A change in resistance takes place when the steel diaphragm is stretched. This change is proportional to the pressure in the fuel rail. The signal is recorded and amplified in the evaluation electronics.

In the event of signal failure the PCM uses a substitute value.

Knock sensors

Installation position of the knock sensors

Two knock sensors are located on the intake side of the cylinder block to detect knocking or pinging of the engine. They are located between cylinders 1/2 and between cylinders 3/4.

The term "knocking" is used to describe combustion processes in which flame speeds in the region of the speed of sound occur. This can happen particularly towards the end of the combustion process if, after the normal combustion process has started, unburned air/fuel mixture on the combustion chamber walls self-ignites under the arising increase in pressure.

The pressure peaks which occur in the process can damage the pistons, cylinder head gasket and the cylinder head.

Swirl valve position sensor

The swirl valve position sensor is used to determine the position of the swirl valves.

Sliding contacts move up and down a variable resistor as the swirl valves open and close.

The PCM can then use the resulting variable voltage signal to calculate the exact position of the swirl valves.

A reference voltage of 5 V is applied to the swirl valve position sensor.

In the event of signal failure only homogeneous mode is permitted.

Exhaust gas temperature sensor

The exhaust gas temperature sensor is used to monitor the 3-way catalytic converter and for diagnosis of the NOx catalytic converter.

The exhaust gas temperature sensor monitors the exhaust gas temperatures required for the optimum conversion process (conversion of the trapped NOx emissions) of the NOx catalytic converter.

In addition, the exhaust gas temperatures are also monitored during the desulphurisation process.

The measuring range of the exhaust gas temperature sensor is -40 ... 1,000 °C. A reference voltage of 5 V is present at the sensor.

The optimum storage capacity of the NOx catalytic converter is given at a temperature of approximately 300 ... 400 °C. During the desulphurisation process, exhaust gas temperatures of between approximately 600 ... 650 °C occur.

In the event of signal failure a substitute value is used for the calculations. This value is taken from a temperature model stored in the PCM.

Heated Oxygen Sensors (HO2S)

Upstream HO2S

The HO2S used in the upstream position (ahead of the 3-way catalytic converter) is a planar broadband HO2S.

This broadband HO2S enables measurements to be performed on exhaust gas which deviates from the stoichiometric ratio (lambda = 1).

The measuring range is from lambda = 0.75 ... 2.8. This extended measuring range makes it possible to regulate the air/fuel mixture both with a lean air/fuel mixture (lambda > 1, stratified mode) and with a rich air/fuel mixture (lambda < 1, NOx trapped, desulphurisation).

The HO2S is equipped with a 6-pin electrical connector.

The adjacent diagram shows the pumping current of the broadband HO2S as a function of the air ratio of the exhaust gas.

The characteristic curve of the broadband HO2S is steady (linear), without a lambda-jump.

The relatively low measuring current is converted to a voltage signal in an internal evaluation circuit in the PCM.

Downstream HO2S

The downstream HO2S is a planar two-point HO2S which serves as a guide probe. Its signal is a direct indication of the reduction of exhaust gas emissions by the pre-catalytic converter.

Optimum conversion of harmful emissions depends on the accuracy of the lambda window, which can only be ensured if the residual errors of the upstream HO2S are compensated for.

The disturbing influence exerted by residual pollutants on the downstream HO2S after the pre-catalytic converter is less by comparison. Therefore the value measured for the upstream HO2S can be corrected accordingly, allowing the above faults to be eliminated.

Furthermore, the downstream HO2S regulates the correction of the oxygen fill level of the pre-catalytic converter.

If the voltage of the downstream HO2S drops below a certain value, this indicates that the level of oxygen passed through the catalytic converter is incorrect, which in turn leads to an increase in NOx emissions. This is counteracted with a fast correction.

The aims of the closed-loop control with the downstream HO2S are:

• To correct residual errors of the upstream HO2S and therefore to establish the long-term stability of the lambda window.
• To correct short-term disturbances of the oxygen levels of the pre-catalytic converter.
• Diagnosis of the pre-catalytic converter.

In addition, the downstream HO2S also serves for the long-term correction of the lambda control of the upstream HO2S and is used for diagnosis of the 3-way catalytic converter within the framework of the European on-board diagnosis.

The voltage reading for the downstream HO2S at which the emissions of harmful pollutants are minimised is between 0.58 and 0.63 V.

At a probe voltage of approximately 0.6 V (lambda = 1), a good and consistent conversion of exhaust gas is achieved in the 3-way catalytic converter in homogeneous mode.

If the system is in stratified mode, then the probe voltage of the downstream HO2S drops below 0.6 V. The substantial increase in NOx particles can no longer be converted by the 3-way catalytic converter.

The downstream NOx catalytic converter traps the NOx emissions until the next release of trapped nitrogen oxides.

HO2S for NOx release

The HO2S for NOx release is also a two-point HO2S and is arranged directly downstream of the NOx catalytic converter.

It corrects the model-based PCM process used to detect saturation of the NOx catalytic converter.

In order to detect saturation of the NOx catalytic converter, the PCM needs to calculate the mass flow of the exhaust gas. The intake air mass and the injected fuel quantity are used to do this.

In stratified mode (lambda >1), the nitrogen oxides are trapped in the NOx catalytic converter in the form of barium nitrate.

At certain model-based intervals, regeneration of the NOx catalytic converter is started. For this purpose the mixture is enriched for a few seconds (lambda < 0.8).

If the voltage of the HO2S for NOx release increases significantly, then this indicates a high HC value. The system stops the conversion process in response to this.

NOTE:The times in seconds represent guide figures which may vary according to the age of the NOx catalytic converter and the type of fuel used.

The time "c" represents a measure for the NOx storage capacity. If the time "c" drops below a certain limit then the desulphurisation of the NOx catalytic converter is started. If the storage capacity of the NOx catalytic converter does not improve afterwards, then the system decides that the NOx catalytic converter is defective and a corresponding trouble code is set.

Actuators

Fuel metering valve

The fuel metering valve on the high-pressure pump allows the fuel to be metered as required (demand-controlled fuel metering).

This solenoid valve ensures that only just as much fuel is pumped to the fuel rail as is required for fuel injection and as is required to maintain the necessary fuel pressure.

Demand-controlled fuel metering is ensured by the PCM as a function of the specified duty cycle.

The fuel metering valve is fully opened in its currentless state.

The fuel metering valve is supplied with a reference voltage between 11 … 14 V.

Swirl valve stepper motor

The drive for the swirl valves for the different airflow conditions (stratified and homogeneous modes) is provided by means of a stepper motor.

The stepper motor essentially comprises two coils. In the holding state only one coil is supplied with a voltage.

The length of time for which the stepper motor is actuated by the PCM is limited by the swirl valve positioning sensor. This means that the swirl valves are controlled in a closed loop control layout.

Components of the electronic engine power control system

The electronic engine power control system comprises the following components:

• APP sensor (1),
• PCM (2),
• Electronic throttle valve (3).

In the electronic engine power control system the PCM performs the actuation of the throttle valve.

The primary variable used to determine the position of the throttle valve is the position of the accelerator pedal. Various other influencing variables (sensor signals, 4) are taken into account by the PCM and used to perform corresponding corrections.

Electronic throttle valve

Sectional view

In the electronic engine power control system, the electronic throttle valve comprises the throttle valve, the drive motor which is integrated in the housing, the throttle valve position sensors and the gearing.

The weight-optimised DC motor drives the intermediate pinion via the drive pinion. The intermediate pinion in turn drives the throttle valve actuation wheel.

This opens the throttle valve against the spring force of the return spring. The return spring ensures that the throttle valve closes automatically in the event of a fault.

However, when the motor is currentless the throttle valve does not close completely. Instead it remains open at a mechanical stop in the so-called emergency air position.

The position of the throttle valve is determined exactly by the throttle valve position sensors.

Initialisation of the electronic throttle valve

In order to determine the exact throttle valve position, the end stops of the throttle valve need to be determined by the PCM.

An initialisation procedure (learning procedure) needs to be performed whenever the electronic throttle valve or the PCM have been replaced, plus whenever the battery has been disconnected.

Conditions for initialisation:

• Engine off (vehicle stationary)
• Accelerator pedal not depressed
• Battery voltage 11 ... 14 V

The initialisation of the PCM takes place as follows:

• after connecting the battery, turn the ignition key to the ON position;
• wait approximately 30 seconds until the initialisation is complete. It is then possible to start the engine.

EVAP system - special features for the 1.8L Duratec SCi engine

Only restricted regeneration of the carbon canister is possible while the engine is operating in stratified mode.

This is because the engine is run almost completely without throttle restriction in stratified mode (the intake manifold vacuum is not sufficient).

This results in a reduced regenerating gas flow compared to the homogeneous mode. If, for example, this is not sufficient when the fuel vaporises, then the engine needs to be operated in homogeneous mode until the initially high fuel concentration in the regenerating gas flow has dropped again.