See Figures 1 and 2
Basically, four electronic ignition systems were used in Ford Motor Company vehicles from 1979-88:
- DuraSpark I-1979-1980
- DuraSpark II-1979-1988
- DuraSpark III-1980-1984
- EEC-IV Thick Film Integrated (TFI)-1984-1988
In 1977, the first DuraSpark systems were introduced. These systems, DuraSpark I and DuraSpark II, are nearly identical in operation and appearance. DuraSpark I uses a special control module which senses current flow through the ignition coil and adjusts the dwell, or coil on-time 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, since the ignition system could inadvertently fire while performing ignition system services (such as distributor cap removal) if the ignition is ON . During its limited use, DuraSpark I was initially restricted to California vehicles equipped with an 8-302 engine. The more widely used DuraSpark II systems are easily identified by their two-piece distributor cap, on which all of the terminals, including the center tower, are the same height.
On some applications over the years, the DuraSpark II system has utilized different ignition modules designed to perform additional functions. Some 1978 and later engines use a special DuraSpark Dual Mode ignition module, equipped with an altitude sensor and an ignition timing vacuum switch (or pressure switches on turbocharged engines). 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 modules have three wiring harnesses, rather than the standard two.
Some 1981 and later DuraSpark II systems, found in vehicles equipped with 8-255 and 8-302 cu. in. engines, utilize a Universal Ignition Module (UIM) which includes a run-retard function. By responding to a second control signal, the UIM provides additional spark timing control for certain operating conditions. The operation of this module is basically the same as that of the DuraSpark Dual Mode module.
Another variation in DuraSpark II ignition modules involves 1981 49-state and 1982 Canadian vehicles equipped with 4-140 engines and automatic transmissions. These vehicles have a Dual Mode Crank Retard ignition module, which has the same function as the DuraSpark II module, plus an ignition timing retard function that is operational during engine cranking. The spark timing retard feature eases engine starting, but allows normal timing advance as soon as the engine is running. This module can be identified by the presence of a white connector shell on the four-pin connector at the module.
In 1980, the DuraSpark III system was introduced. This version is based on the previous systems, but the input signal is controlled by the EEC (Electronic Engine Control) system, rather than as a function of engine timing and distributor armature position. The EEC system controls spark advance in response to various engine sensors. These include a crankshaft position sensor, which replaces the stator assembly and armature previously located in the distributor assembly. As a result, the DuraSpark III distributor serves only to distribute high voltage generated by the ignition coil. The relationship of the distributor rotor to cap is important for proper high voltage distribution. For this reason, the DuraSpark III distributor is secured to the engine and the distributor rotor positions are adjustable.
An exception involves the 6-232 engine, in which the DuraSpark III distributor assembly is a modified DuraSpark II design. Rotor alignment is not adjustable on these applications.
The distributor, rotor, cap and control module are unique to the DuraSpark III system, while 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 between systems.
Finally, 1984 marked the introduction of Ford's EEC-IV Thick Film Integrated (TFI) ignition system. The EEC-IV system's universal distributor has a diecast base which incorporates an externally mounted TFI-IV ignition module. It also contains a Hall effect vane switch stator assembly and provision for fixed octane adjustment. No distributor calibration is necessary and initial timing adjustment is normally not required. The primary function of the EEC-IV system's universal distributor is to direct 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. The Hall effect switch in the distributor consists of a Hall effect 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 sides of the switch, the magnetic path is completed, whereby the Hall effect device is turned on and a signal is sent. The voltage pulse (signal) is used by the EEC-IV system for sensing crankshaft position and computing the desired spark advance based on engine demand and calibration.
With the ignition switch ON , the primary circuit is on and the ignition coil is energized. When the armature spokes approach the magnetic pickup coil assembly, they induce the voltage which tells the amplifier module to turn the coil primary current off. A timing circuit in the amplifier module will turn the current on again after the coil field has collapsed. When the current is on, it flows from the battery through the ignition switch, the primary windings of the ignition coil, and through the amplifier module circuits to ground. When the current is off, the magnetic field in the ignition coil is allowed to collapse, inducing a high voltage into the coil's secondary windings. High voltage is produced each time the field is thus built and collapsed. When DuraSpark is used in conjunction with the EEC (DuraSpark III), the EEC computer tells the DuraSpark module when to turn the coil primary current off or on. In this case, the armature position is only a reference signal of engine timing, used by the EEC computer (in combination with other reference signals) to determine optimum ignition spark timing.
The high voltage flows through the ignition coil high tension lead to the distributor cap where the rotor distributes it to one of the cap terminals. This process is repeated for every power stroke of the engine.
Ignition system troubles are caused by a failure in the primary and/or the secondary circuit, incorrect ignition timing or incorrect distributor advance. Circuit failures may be caused by shorts, corroded or dirty terminals, loose connections, unsound wire insulation, a defective pick-up coil assembly or amplifier module, a cracked distributor cap/rotor, or fouled spark plugs.
If an engine starting or operating problem is attributed to the ignition system, start the engine and verify the complaint. On engines that will not start, be sure that there is gasoline in the fuel tank and that fuel is reaching the carburetor or injectors. Then locate the ignition system problem using the following procedures.