Ignition System: Service Precautions

TFI-I

Concerns of no start, slow start, misfire, lower power at part throttle and/or poor fuel economy may be caused by spark tracking and crossfire in the distributor cap and/or a cracked diaphragm in the distributor vacuum advance assembly. When troubleshooting these problems, the ``Spark Plug Firing Voltage Test'' should be performed. If the display is not satisfactory, the distributor cap, rotor and vacuum advance diaphragm should be replaced. Only a vented cap (part No. E5FZ-12106-C), blade rotor (part No. E5FZ-12200-A) and a vented diaphragm assembly of the same calibration should be used.


TFI IV

Do not change timing by use of different octane rods without first having the proper authorization as federal emission requirements will be affected.

Except for the cap, rotor, module, O-ring, and octane rod, no other distributor assembly parts are replaceable. There is no calibration required with the universal distributor.

Do not attempt to lift module from mounting surface prior to moving entire TFI module toward distributor flange as you will break the pins at the distributor/module connector.

The rotor is a multi-point rotor which eliminates the need for silicone compound on the rotor tip.

Some engines may be equipped with a security type distributor holddown bolt. Use Tool T82L-12270-A or equivalent to remove the distributor.


CIRCUIT TESTS - TFI IV

The primary winding of the ignition coil may be damaged if there is a short to ground in the wiring harness containing the tachometer circuit. Before replacing the ignition coil due to a no start condition, measure and record battery voltage as well as voltage between coil negative terminal and ground with ignition key in the On position. If there is more than a 1 volt difference between the readings, inspect tachometer circuit for a short to ground and repair as necessary.
If a short to ground is caused by a failed TFI-IV module, the ignition coil primary winding may be damaged. Because this type of malfunction will not be identified using standard testing procedures, the following steps should be taken when servicing a weak or no spark condition: check for spark as described in ``Test 1.'' If there is no spark, test coil primary resistance as described in ``Test 3.'' If coil primary resistance is satisfactory, continue with diagnostic procedure described in ``Test 1.'' If coil primary resistance is not satisfactory, replace coil and recheck for weak or no spark. If spark is now satisfactory, the problem no longer exists. If spark is still not satisfactory, continue with diagnostic procedure described in ``Test 1.''