The Ford V-8 Engine Workshop|
Duraspark II Electronic Ignition
Duraspark II electronic ignition was used on 1977 to 1984 Ford V-8 passenger car and light truck
engines. This article refers to the Duraspark II control module with a BLUE strain relief bushing,
one 4-pin connector, and one 2-pin connector. Another version of the system has
an additional 3-pin wiring connector, and two YELLOW strain relief bushings. Discussion of
that "dual mode" system will be added later.
Duraspark II uses a variable reluctance magnetic pickup in place of traditional breaker points. The signal from this pickup is amplified by the control module to drive the ignition coil. The module hold a fixed dwell time, and features automatic retard while cranking to reduce the load on the starter motor.
The high voltage ignition coil, wider spaced terminals of the distributor cap, and 8mm silicone insulated high tension wires permit the use of wider spark plug gaps. This results in a more powerful spark which is more likely to ignite the air-fuel mixture. Due to the higher voltage operation of the system, silicone dielectric compound should be applied to the insides of the spark plug wire boots, at both the cap and plug ends. This special grease is available at most auto parts stores, or under Ford part # D7AZ-19A331-A. This compound should also be applied to the tip of the distributor rotor.
The larger diamter cap and better wires are not required, however, if the older tighter spark plug gaps are maintained. Under some circumstances you may need to retain the old style smaller cap. For example, you might not be able to fit the larger cap under a Monte Carlo bar in an early Mustang, for example.
This ignition system offers the benefits of reduced maintenance, smoother engine operation with improved idle, better fuel economy, and reduced emissions.
Duraspark II Major Components
|The Duraspark II control module has a BLUE strain relief bushing, one 4-pin connector, and one 2-pin connector. Shown here on the firewall of my '72 Bronco.|
|The Duraspark II distributor uses a magnetic pickup in place of traditional breaker points.|
|The Duraspark II ignition coil is capable of generating a higher voltage than the regular coil. The wiring is attached via a special snap-on connector. Power is supplied to the coil in the same fashion as the older breaker point ignition.|
|The Duraspark II distributor cap is larger in diameter to allow the high tension terminals to be spaced farther apart. This prevents crossfiring with the higher coil voltage. The cap is made in two parts; the lower section is an adapter to fit the standard Ford V-8 distributor body. The rotor is longer and taller fit this cap.|
This ignition system is a popular swap into earlier cars and trucks. Wiring it up is
quite straightforward. This is most easily accomplished by making a trip to your
favorite junkyard and rounding up all the parts. Be sure to get the wiring harnesses
connecting the module, distributor, and coil, as well as the male end of the 2-pin connector
and some length of its wires. Note that the colors of the wires shown in the diagram below
are at the module itself. The wires in the harness tend to be different colors on
different cars and years.
Power is supplied to the BATT or + coil terminal in the same fashion as the older breaker point ignition. Under normal "run" conditions, power comes from the key switch through a length of resistance wire (0.8 to 1.6 ohms). This wire is normally pink and is found under the dash. During cranking, this resistance is bypassed by a wire from the "I" terminal on the starter relay. In most applications, the wire that used to power the coil can power the new coil.
The system is grounded through the black wire in the harness to a point inside the distributor.
Only one new connection is required. The module receives its power through the red wire in the 2-pin connector. This must come from the key switch terminal that is "hot in start or run". If your car has an idle positioner solenoid, the wire powering that may be used to power the module.
Optionally, but a good idea, the white wire in the 2-pin connector is connected to the "S" terminal on the starter relay. This is used as a cranking indicator to the module, to retard the timing slightly to ease the load on the starter motor.
Use the factory harness for the rest of the wires. The green wire runs from the module to the TACH or minus coil terminal. This is where you can connect a normal tachometer. The orange and purple wires from the module run to the pickup inside the distributor.
Retrofitting the Duraspark II system to earlier small block V-8 cars is a popular
swap. A few things should be considered when selecting the parts.
Distributors do not physically interchange between a 302 and 351W. 351W engines have a larger oil pump driveshaft. The end of the distributor shaft is also larger to accomodate this difference. The 289/302 distributor shaft diameter is 0.467", 351W is 0.531". At the junkyard, small blocks tend to all look alike. Be sure to go to the junkyard armed with a 1/2" distributor wrench. On cars loaded with power steering and air conditioning it can be quite a challenge to remove the distributor hold-down bolt without the proper tools.
Also be sure to use the correct distributor drive gear. The material must be compatible with the camshaft. Most normal cast iron camshafts require a cast iron distributor gear. Hydraulic roller camshafts are generally steel, and require a steel gear. Some aftermarket camshaft manufacturers specify the use of a bronze gear. Gears in all combinations of size and material are available from Ford Motorsport.
When installing the new distributor, it is always a good idea to use a new O-ring.
The control module doesn't like to get overheated. Be sure to mount it somewhere away from heat sources. (if such a place exists under a hood)