See Figures 1, 2, 3, 4, 5 and 6
Several different ignition systems have been used in Ford/Mercury vehicles from 1968-88:
- Duraspark I
- Duraspark II
- Duraspark III
- TFI (EEC-IV)
In 1974, Ford/Mercury began to use breakerless ignition systems. The first of these electronic ignition systems was originally just referred to as the breakerless ignition system, but later, in 1977, it became known as Duraspark. The Duraspark I system, and the next version, Duraspark II were nearly identical in operation, and virtually identical in appearance. The Duraspark I uses a special control module which senses current flow through the ignition coil and adjusts the coil for maximum spark intensity. If the Duraspark I module senses that the ignition is ON , but the distributor shaft is not turning, the current to the coil is turned OFF by the module. The Duraspark II system does not have this feature. The coil is energized for the full amount of time that the ignition switch is ON . Keep this in mind when servicing the Duraspark II system, as the ignition system could inadvertently fire while performing ignition system services (such as distributor cap removal) while the ignition is ON . All Duraspark II systems are easily identified by having a two-piece, flat topped distributor cap.
Duraspark I was discontinued after the 1981 model year.
In 1980, the new Duraspark III system was introduced. This version is based on the previous systems, but the input signal is controlled by the EEC system, rather than as function of engine timing and distributor armature position. The distributor, rotor, cap, and control module are unique to this system; the spark plugs and plug wires are the same as those used with the Duraspark II system. Although the Duraspark II and III control modules are similar in appearance, they cannot be interchanged.
Some 1978 and later engines use a special Duraspark Dual Mode ignition control module. This module is equipped with an altitude sensor, and an economy modulator. This module, when combined with the additional switches and sensor, varies the base engine timing according to altitude and engine load conditions. Duraspark Dual Mode ignition control modules can be identified by the three wiring harnesses emerging from the control module.
Some 1981 and later Duraspark II systems used with the 5.0L engine are quipped with a Universal Ignition Module (UIM) which includes a run/retard function. The operation of the module is basically the same as the Duraspark Dual Mode module.
The (EEC-IV) distributor has a diecast base which incorporates an externally mounted TFI-IV ignition module, and contains a Hall Effect vane switch stator assembly and provision for fixed octane adjustment. No distributor calibration is required and initial timing adjustment is normally not required. The primary function of the EEC-IV Universal Distributor system is to direct a high secondary voltage to the spark plugs. In addition, the distributor supplies crankshaft position and frequency information to a computer using a Profile Ignition Pickup (PIP). The Hall Effect switch in the distributor consists of a sensor device on one side and a magnet on the other side. A rotary cup which has windows and tabs rotates and passes through the space between the device and the magnet. When a window is between the sides of the switch the magnetic path is not completed and the switch is off, sending no signal. When a tab passes between the switch the magnetic path is completed, and the Hall Effect device is turned on and a signal is sent. The voltage pulse (signal) is used by is EEC-IV system for sensing crankshaft position and computing the desired spark advance based on engine demand and calibration.