Mark Houlahan
Brand Manager, Mustang Monthly
March 1, 2003
The Performance Distributors 5.0 Fire Power Ignition System includes everything you see here-except for your choice of spark plug-for a complete, major tune-up. We encourage you to inspect all your underhood wear items at this time. Our subject GT needed a new serpentine belt and had some cracked and failing vacuum hoses to be taken care of as well.

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.

To begin the tune-up, the three-year-old plug wires get the heave-ho from the distributor cap. If you're really paranoid about the engine's firing order, you can replace the wires and plugs one at a time, but it's easier and much faster to remove everything at once. All you have to remember is the firing order (see the sidebar Which Way Does It Go, George?).

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.

To remove the TFI module you will need a 1/2-inch-sized 1/4-inch-drive deep socket (plus a 1/2-inch socket or distributor wrench to loosen the distributor). A shallow socket will not reach the bolt retaining the TFI module. While our Craftsman socket works flawlessly, some deep sockets are too thick to be inserted into the module. You can also purchase a module tool from most auto parts stores that allows turning the bolts with a 1/4-inch wrench.

So you see, just throwing new plugs into your 5.0 is only a Band-Aid. Do it right and do it all to get the best performance for your maintenance dollars. The '89 GT we're tuning up here will benefit from the complete Performance Distributors 5.0 Fire Power Ignition system ($224.01, available for '86-'93 and '94-'95 5.0s), a set of Denso Iridium plugs, and a thorough ignition-system inspection. While we didn't show it here due to space constraints, a new PCV valve (found at the rear of the lower intake), fuel filter, and serpentine belt were added as well. Take a look at what we've done, then take a peek under your own hood. We bet you need to do some work.

So you've pulled off your plug wires in a fit of frustration. Maybe you meant to replace only one wire at a time but another fell off during your work. What do you do? Have no fear-Captain Firing Order is here! [We call Tech Editor Houlahan that 'cause he's screwed up the firing order so much. Don't fret, however. After several lashings with a bad plug wire, he actually has it straight for you.-Ed.]

* The firing order of the 5.0 small blocks in H.O. or 351 trim is: 1-3-7-2-6-5-4-8 (non H.O.s swap the 3-7 and 5-4 for 1-5-4-2-6-3-7-8).

We found the rearmost of the two module retaining bolts accessible only by removing the lower distributor cap adapter and rotating the distributor further. Don't worry about your lineup marks, as the cap adapter is indexed to install only one way.

* The distributor rotor rotation is counterclockwise.

* All Ford and most aftermarket distributor caps are clearly marked. Cylinder identification for the No. 1 cylinder has a large "1" on it.

* Cylinder locations on all V-8 Fords are as follows: Passenger side, front to back is 1-2-3-4 Driver side, front to back is 5-6-7-8

So, put it all together and you have your answers. Start with cylinder No. 1 on your distributor cap. In a counterclockwise rotation, install the spark-plug wires, routing the wires to their correct plugs one at a time. You'll be back up and running in no time. Thank me later.

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