Ford Pick-ups and Broncos 1987-1996 Repair Guide

TFI-IV System



See Figures 1 and 2

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Fig. Fig. 1: TFI schematic

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Fig. Fig. 2: Exploded view of the TFI components

The Thick Film Integrated (TFI-IV) ignition system uses a camshaft driven distributor with no centrifugal or vacuum advance. The distributor has a diecast base, incorporating a Hall effect stator assembly. The TFI-IV system module is mounted on the distributor base, it has 6 pins and uses an E-Core ignition coil, named after the shape of the laminations making up the core.

The TFI-IV module supplies voltage to the Profile Ignition Pick-up (PIP) sensor, which sends the crankshaft position information to the TFI-IV module. The TFI-IV module then sends this information to the EEC-IV module, which determines the spark timing and sends an electronic signal to the TFI-IV ignition module to turn off the coil and produce a spark to fire the spark plug.

The operation of the universal distributor is accomplished through the Hall effect stator assembly, causing the ignition coil to be switched off and on by the EEC-IV computer and TFI-IV modules. The vane switch is an encapsulated package consisting of a Hall sensor on one side and a permanent magnet on the other side.

A rotary vane cup, made of ferrous metal, is used to trigger the Hall effect switch. When the window of the vane cup is between the magnet and the Hall effect device, a magnetic flux field is completed from the magnet through the Hall effect device back to the magnet. As the vane passes through the opening, the flux lines are shunted through the vane and back to the magnet. A voltage is produced while the vane passes through the opening. When the vane clears the opening, the window causes the signal to go to 0 volts. The signal is then used by the EEC-IV system for crankshaft position sensing and the computation of the desired spark advance based on the engine demand and calibration. The voltage distribution is accomplished through a conventional rotor, cap and ignition wires.


Spark Plug Wire Resistance

Whenever the high tension wires are removed from the plugs, coil, or distributor, silicone grease must be applied to the boot before reconnection. Use a clean small screwdriver blade to coat the entire interior surface with Ford silicone grease D7AZ-19A331-A, Dow Corning #111, or General Electric G-627.

  1. Use spark plug wire removal pliers, or grasp firmly at the boot (not the wire itself) and remove the wires from the plugs, then remove the distributor cap.
  3. Measure the resistance through the distributor cap at that end. Resistance on these wires must not exceed 5,000 ohms per foot. Do not pierce any ignition wire for any reason. Measure only from the two ends.


The air gap between the armature and magnetic pick-up coil in the distributor is not adjustable, nor are there any adjustment for the amplifier module. Inoperative components are simply replaced. Any attempt to connect components outside the vehicle may result in component failure.


After performing any test which requires piercing a wire with a straight pin, remove the straight pin and seal the holes in the wire with silicone sealer.

Wiring Harness
  1. Disconnect the wiring harness connector from the TFI module; the connector tabs must be PUSHED to disengage the connector. Inspect the connector for damage, dirt, and corrosion.
  3. Attach the negative lead of a voltmeter to the base of the distributor. Attach the other voltmeter lead to a small straight pin. With the ignition switch in the RUN position, insert the straight pin into the No. 1 terminal of the TFI module connector. Note the voltage reading. With the ignition switch in the RUN position, move the straight pin to the No. 2 connector terminal. Again, note the voltage reading. Move the straight pin to the No. 3 connector terminal, then turn the ignition switch to the START position. Note the voltage reading then turn the ignition OFF .
  5. The voltage readings should all be at least 90 percent of the available battery voltage. If the readings are okay, proceed to the Stator Assembly and Module test. If any reading is less than 90 percent of the battery voltage, inspect the wiring, connectors, and/or ignition switch for defects. if the voltage is low only at the No. 1 terminal, proceed to the ignition coil primary voltage test.

Stator Assembly and Module
  1. Remove the distributor from the engine.
  3. Remove the TFI module from the distributor.
  5. Inspect the distributor terminals, ground screw, and stator wiring for damage. Repair as necessary.
  7. Measure the resistance of the stator assembly, using an ohmmeter. If the ohmmeter reading is 800-975 ohms, the stator is okay, but the TFI module must be replaced. If the ohmmeter reading is less than 800 ohms or more than 975 ohms; the TFI module is okay, but the stator module must be replaced.
  9. Repair as necessary and install the TFI module and the distributor.

Primary Circuit Continuity

This test is performed in the same manner as the previous Wiring Harness test, but only the No. 1 terminal conductor is tested (ignition switch in Run position). If the voltage is less than 90 percent of the available battery voltage, proceed to the coil primary voltage test.