General information and precautions

Ignition system - transistorised type / General information and precautions

General information
TCI-H system
The transistorised (TIC-H) ignition system functions in a similar manner to that described in Part A of this Chapter for the contact breaker system, with the following exceptions.

An electronic sender unit replaces the contact points and condenser in the distributor and a remotely-mounted electronic switch unit controls the coil primary circuit (see illustrations).

1.1a Transistorised ignition system components – 1.05 and 1.3 litre engines

1.1b Transistorised ignition system components – 1.6 litre engine

Ignition timing is advanced and retarded automatically, to ensure that the spark occurs at just the right instant for the particular load at the prevailing engine speed.

Ignition advance is controlled both mechanically and by a vacuum-operated system. The mechanical governor mechanism comprises two weights, which move out from the distributor shaft as the engine speed rises due to centrifugal force. As they move outwards they rotate the cam relative to the distributor shaft, and so advance the spark.

The weights are held in position by two light springs, and it is the tension of the springs which is largely responsible for correct spark advancement.

Vacuum control comprises a diaphragm, one side of which is connected via a small bore pipe to the inlet manifold, and the other side to the distributor baseplate. Depression in the inlet manifold, which varies with engine speed and throttle opening, causes the diaphragm to move, so moving the baseplate, and advancing or retarding the spark. A fine degree of control is achieved by a spring in the vacuum assembly.

Digifant system
Fitted to the 1.8 litre (code PB and PF) engine, the Digifant ignition system uses the TCI-H system described above but in addition, incorporates a knock sensor which senses the onset of pre-ignition and retards ignition timing accordingly. Normal ignition timing is automatically adjusted by the Digifant control unit which also controls the fuel injection system. Because of this, there are no centrifugal advance weights in the distributor (see illustration).

1.5 Digifant ignition system components

Work procedures are basically as given for the TIC-H system , except for those described in the relevant Sections.

Precautions
In addition to the precautions listed in Part A of this Chapter, note the following: a) When turning the engine at starter speed without starting, the HT lead must be pulled from the centre of the distributor cap and kept earthed to a suitable part of the engine or bodywork
b) If the system develops a fault and it is necessary to tow the vehicle with the ignition on, the wiring must be disconnected from the TCI-H switch unit c) Do not under any circumstances connect a condenser to the coil terminals