The only adjustment available on the TFI-IV system is the timing. Refer to Section 1 for Timing inspection and adjustment.
Diagnosis & Testing
Cylinder Drop Test
The cylinder drop test is performed when an engine misfire is evident. This test helps determine which cylinder is not contributing the proper power. The easiest way to perform this test is to remove the plug wires one at a time from the cylinders with the engine running.
- Place the transmission in P , engage the emergency brake, and start the engine and let it idle.
- Using a spark plug wire removing tool, preferably, the plier type, carefully remove the boot from one of the cylinders.
- The engine will sputter, run worse, and possibly nearly stall. If this happens reinstall the plug wire and move to the next cylinder. If the engine runs no differently, or the difference is minimal, shut the engine off and inspect the spark plug wire, spark plug, and if necessary, perform component diagnostics as covered in this section. Perform the test on all cylinders to verify the which cylinders are suspect.
The best way to perform this procedure is to use a spark tester (available at most automotive parts stores). Three types of spark testers are commonly available. The Neon Bulb type is connected to the spark plug wire and flashes with each ignition pulse. The Air Gap type must be adjusted to the individual spark plug gap specified for the engine. The last type of spark plug tester looks like a spark plug with a grounding clip on the side, but there is no side electrode for the spark to jump to. The last two types of testers allows the user to not only detect the presence of spark, but also the intensity (orange/yellow is weak, blue is strong).
- Disconnect a spark plug wire at the spark plug end.
- Connect the plug wire to the spark tester and ground the tester to an appropriate location on the engine.
- Crank the engine and check for spark at the tester.
- If spark exists at the tester, the ignition system is functioning properly.
- If spark does not exist at the spark plug wire, perform diagnosis of the ignition system using individual component diagnosis procedures.
Removal & Installation
- Pulling on the connector boot, disconnect the high tension lead at the coil.
- Disconnect the wiring at the ignition coil.
- Remove the ignition coil-to-bracket attaching screws, then remove the coil.
- Install the coil, tightening the screws to 25-35 inch lbs. (3-4 Nm).
- Connect the ignition coil wiring harness and the high tension lead.
The first check of the primary ignition coil is to verify that there is battery voltage at the BATT terminal on the coil. A DVOM is recommended to test for voltage. Turn the ignition switch to the RUN position and connect the negative lead of the DVOM to a ground or the negative post/cable clamp on the battery. Connect the other lead of the DVOM to the BATT terminal on the coil. The voltage measured should be within 1 volt of the battery voltage as measure across the posts of the battery.
After verifying there is battery voltage present, the next check is to verify the operation of the coil primary ground which is received at the coil from the ICM (Ignition Control Module). This check is accomplished using a test lamp and connecting the lead of the test lamp to the ground or the battery negative post/cable clamp. Connect the test lamp to the ground side of the coil (the connection opposite the BATT terminal on the coil on the other side of the coil tower) and crank the engine. The light should blink on and off repeatedly as long as the engine cranks or runs. If the light does not blink the problem is either in the ICM or the PIP signal generated by the sensor inside the distributor.
The final check of the primary coil is to check the resistance of the coil. This is accomplished by using a DVOM and probing the BATT terminal and the coil ground terminal. Measure the resistance between the two terminals. If the resistance is between 0.3 and 1.0 ohm, the primary ignition coil is within specifications. If the reading differs from this specification, replace the coil and retest.Secondary Windings
The coil secondary resistance is the final check of the ignition coil. Use a DVOM to measure the resistance between the BATT terminal to the high voltage terminal of the ignition coil. If the reading is between 6,500-11,500 ohms, the ignition coil is OK. If the reading is less than 6,500 or more than 11,500 ohms, replace the ignition coil. If the secondary windings are within specifications and the primary circuit also tests within specifications, inspect and test the spark plug wires and the spark plugs, refer to Section 1.
Removal & Installation
The ignition module is located on the driver's side fender apron.
- Disconnect the negative battery cable.
- Detach the module harness connector.
- Remove the heat sink-to-fender retaining screws and remove the heat sink and module from the vehicle.
- Remove the TFI module-to-heat sink retaining screws and remove the module from the heat sink.
- Coat the TFI module baseplate with a thin layer of dielectric grease (FD7AZ-19A331-A or its equivalent).
- Place the TFI module on the heat sink.
- Tighten the TFI module-to-heat sink retaining screws to 11-16 inch lbs. (1.2-1.8 Nm).
- Install the heat sink onto the fender and tighten the heat sink-to-fender retaining screws to 80-124 inch lbs. (9-14 Nm).
- Attach the module harness connector.
- Connect the negative battery cable.
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.