Contact breaker ignition system The ignition system is divided into two circuits, low tension (primary) and high tension (secondary). The low tension circuit consists of the battery, ignition switch, primary coil windings and the contact breaker points and condenser. The high tension circuit consists of the secondary coil windings, the heavy ignition lead from the centre of the distributor cap to the coil, the rotor arm and the spark plug leads and spark plugs.

When the system is in operation, low tension voltage is changed in the coil into high tension voltage by the opening and closing of the contact breaker points in the low tension circuit. High tension voltage is then fed, via the carbon brush in the centre of the distributor cap, to the rotor arm of the distributor. The rotor arm revolves inside the distributor and each time it comes in line with one of the four metal segments in the distributor cap, which are connected to the spark plug leads, the opening and closing of the contact breaker points causes the high tension voltage to build up and jump the gap from the rotor arm to the appropriate metal segment. The voltage then passes via the spark plug lead to the spark plug, where it finally jumps the spark plug gap before going to earth.

The distributor is driven by a skew gear from the camshaft on the OHV engine and by an offset dog on the end of the camshaft on CVH engines.

The ignition advance is a function of the distributor and is controlled both mechanically and by a vacuum-operated system.

A ballast resistor is incorporated in the low tension circuit between the ignition switch and the coil primary windings. The ballast resistor consists of a grey coloured resistive wire running externally to the main loom between the ignition switch and coil. During starting this resistor is bypassed allowing full available battery voltage to be fed to the coil which is of a low voltage type. This ensures that during starting when there is a heavy drain on the battery, sufficient voltage is still available at the coil to produce a powerful spark. During normal running, battery voltage is directed through the ballast resistor to limit the voltage supplied to the coil to seven volts.

Electronic breakerless ignition The fundamentals of operation of the electronic breakerless ignition system are similar to those described previously for the contact breaker system, however in the breakerless electronic ignition system, the action of the contact breaker points is simulated electronically within the distributor.

Control of ignition advance characteristics is still carried out in the conventional way using mechanical and vacuum systems.

Programmed electronic ignition (RS Turbo models)
The two main components of the system are the electronic control module designated Electronic Spark Control II (ESC II), and a Hall effect electronic ignition distributor.

The distributor is mounted on the flywheel end of the cylinder head, and is driven directly off the camshaft by an offset dog coupling.

Contained within the distributor is a trigger vane, permanent magnet and position sensor.

The trigger vane is a cylindrical disc attached to the distributor shaft and having four slots on its vertical surface, one for each cylinder. The permanent magnet and position sensor are secured to the distributor baseplate in such a way that the vertical surface of the trigger vane passes between them. As the trigger vane rotates, the magnetic field between the magnet and position sensor is interrupted and a series of square wave electronic pulses are produced. This output wave form is sent to the ESC II module and from this, engine speed, ignition advance and idle speed are calculated.

A small bore hose connecting the inlet manifold to a vacuum transducer within the module supplies the unit with information on engine load, and a charge air temperature sensor, which is a temperature sensitive resistor located in the air intake duct, provides information on engine intake air temperature.

From this constantly changing data the ESC II module selects a particular advance setting from a range of ignition characteristics stored in its memory.

With the firing point established, the module switches off the ignition coil primary circuit, the magnetic field in the coil collapses and the high tension voltage is created. At precisely the right instant the ESC II module switches the coil primary circuit back on and the cycle is repeated for each cylinder in turn.

Additionally the ESC II module operates in conjunction with the fuel-injection and turbo systems to provide data on engine rpm to the fuel-injection control module, and to provide an overriding control of turbo boost pressure.

Programmed electronic ignition (1.4 litre fuel injection engines) The ignition system consists of a Hall effect distributor (as described previously for RS Turbo models), TFI IV ignition module, coil and EEC IV module.

The distributor is similar to that used on earlier CVH engine models, but has no centrifugal or vacuum advance mechanisms, the advance functions being carried out by the EEC IV module. The distributor acts as a trigger and provides a pulse signal to the EEC IV module.

The distributor performs the following functions:
a) Sends signals to the EEC IV module to trigger the ignition firing process.

b) Enables the EEC IV module to calculate engine speed from the pulse signals.

c) Distributes HT voltage to the spark plugs.

The TFI (Thick Film Integration) IV module functions as a high current switch by controlling the ignition coil primary LT circuit.

The module is controlled by one of two input signals, either from the Hall effect sensor in the distributor, or from the EEC IV module.

The signal from the distributor passes via the TFI IV module to the EEC IV module. The EEC IV module modifies the signal to provide ignition timing advance relative to engine speed, load and temperature, before returning it to the TFI IV module.

The EEC IV module provides total engine management via the ignition and fuel systems.

From signals received from the various sensors, the module controls the following functions:
a) Ignition timing.

b) Fuel delivery.

c) Deceleration fuelling.

d) Idle speed.

e) Engine overspeed protection.

If the module should fail, the ignition timing will be switched by the TFI IV module (there will be no ignition advance) and fuel will be delivered at a constant rate. This state is known as the Limited Operation Strategy (LOS) and allows the vehicle to be driven, albeit with greatly reduced engine performance and fuel economy.

Should any of the system sensors fail, the EEC IV module will sense this and substitute a single predetermined value for the failed input.

Again, this will allow continued engine operation, with reduced performance and driveability. Under these conditions a self-test code will be stored in the module memory to aid subsequent fault diagnosis by a Ford dealer.

Distributorless ignition system (DIS)
1.4 litre fuel injection engines The mechanical distribution of high tension voltage (by a rotating distributor) is replaced by “static” solid-state electronic components.

The system selects the most appropriate ignition advance setting for the prevailing engine operating conditions from a threedimensional map of values stored in the Electronic Spark Control (ESC) module memory. The module selects the appropriate advance value according to information supplied on engine load, speed, and operating temperature by various sensors.

Engine speed is monitored by a sensor mounted in the cylinder block, which is activated by 35 equally-spaced teeth on the flywheel. A gap occupies the position of the 36th tooth, which denotes 90° BTDC for No 1 cylinder. As the engine speed increases, so does the frequency and amplitude of the signal sent to the ESC module (photos).

Engine load information is provided by a pressure sensor which is integral with the ESC module. The sensor monitors vacuum in the inlet manifold via a hose.

Engine temperature is monitored by an Engine Coolant Temperature (ECT) sensor screwed into the bottom of the inlet manifold.

A DIS coil assembly is mounted on the cylinder block next to No 1 cylinder. The coil has two primary and two secondary windings.

One secondary winding supplies current to numbers 1 and 4 cylinders simultaneously, while the other supplies current to numbers 2 and 3 cylinders. Whenever either of the coils is energised, two sparks are generated. For example, one spark is produced in No 1 cylinder on its compression stroke, while the other spark is produced in No 4 cylinder on its exhaust stroke. The spark in No 4 cylinder is “redundant” and has no detrimental effect on engine performance.

1.6 litre Electronic Fuel Injection engines
The ignition system is under the overall control of the EEC IV engine management module. The module compares the signals provided by the various sensors with engine operating parameters stored in its memory, and varies the engine operating settings directly according to engine load and the prevailing operating conditions.

Ignition is via a Distributorless Ignition System (DIS), similar to that described previously for 1.4 litre fuel injection engines.

The DIS is controlled by the E-DIS 4 module.

Precautions
Warning: The DIS system carries much higher voltages than conventional systems, and adequate precautions must be taken to avoid personal injury. Refer to the “Safety first!” Section at the beginning of this manual before proceeding, and always disconnect the battery negative lead before working on the system It is necessary to take extra care when working on the ignition system, both to avoid damage to semi-conductor devices and to avoid personal injury. Refer to the precautions given in “Safety First!” at the beginning of this manual, with particular reference to the warning concerning ignition HT voltage. Also refer to the precautions at the beginning of Chapter 5A.