5.0 Mustang & Super FordsHow To Engine
Fox Mustang Ignition System - All Fired Up
Performing A Major Tune-Up Can Eliminate Driveability Problems And Add Life To Your Mustang
Horse Sense: There's more to a major tune-up than simply throwing in fresh spark plugs. The entire secondary ignition should be checked and replaced if needed. Using a complete system such as the 5.0 Firepower Ignition Kit from Performance Distributors is an efficient way to get what you need, while saving some money to boot.
Many of our readers are too young to remember points ignitions, but those of us who do are thankful for the advances in electronic ignition systems. However, that's not to say electronic ignitions are maintenance free. Having the proper voltage, clean grounds, and the correct hardware is just as important as a point-gap setting or the proper amount of dwell. And the tools for the job are similar. You'll need a timing light, an ohmmeter, a spark tester, and various sockets and wrenches to get the job done.
On '86-'95 5.0 Mustangs, the ignition system was designed around the Ford Thick Film Ignition system, or TFI as it is known. This system has two basic configurations: '86-'93 and '94-'95. On the '86-'93 version, a nine-pin TFI module mounts directly on the distributor, which is in turn plugged into the Hall Effect sensor inside the distributor bowl. A low-resistance E-core ignition coil and 8mm plug wires round out the system. For '94-'95 models, the only major differences are what's referred to as a "closed-bowl" distributor, and the TFI module, a six-pin design that is mounted remotely to an aluminum heat sink on the passenger inner fender.
The basic ignition-system circuit has two major sides: the primary circuit and the secondary circuit. The primary circuit consists of the battery, the ignition switch, the primary side of the coil, the primary side of the distributor (Hall-Effect trigger), the wiring, and the chassis ground. The secondary side of the ignition system consists of the secondary side of the coil, the secondary side of the distributor (distributor cap and rotor), the spark-plug wires, and the spark plugs. Put all of these items together and you have the ignition system.
As the distributor shaft rotates, the rotary-vane cup attached to it passes through the Hall-Effect sensor part of the Profile Ignition Pickup (PIP), shunting the magnetic flux path (hold the flux capacitor jokes, please). This turning on and off of the Hall-Effect sensor creates a square-wave signal, which the EEC IV uses to determine spark advance. The PIP signal is used along with the Spark Out (SPOUT) signal via comparison from the TFI module to fire the coil.
The E-core coil Ford uses is capable of 45,000 volts of output. How does a coil put out such voltage when it "looks" as if only 12 volts is going into it? Good question. The primary side of the coil does indeed have a 12-volt battery feed going into the coil. If you were to cut open a coil you would see a large secondary winding of wires wrapped by a smaller concentration of primary wiring around it. This 12-volt primary wire, which is wrapped around the secondary windings, creates a magnetic field when the ground side is closed by the distributor (this is your tach signal). When the primary circuit is opened, the magnetic field collapses causing current induction into the secondary winding, which provides the greater voltage. The voltage is then transferred from the coil terminal to the distributor cap via the coil wire. The rotor found inside the distributor is responsible for seeing that the secondary voltage is transferred to the right spark-plug wire, which in turn sends it to the spark plug. The spark plug, which is grounded to the engine via the plug body threads, is the only path to ground for the secondary voltage, thus the voltage will cross the plug gap to ground, causing the spark that ignites the air/fuel mixture in the combustion chamber.