The TFI (Thick Film Ignition) system was an earlier name for the Ignition Module, from about 1984-1992 it was mounted on the distributor.
In your 1994 they have moved it to the Fender on the driver's side and rename it the ICM (Ignition Control Module). The diagram below still calls it the TFI Module.

It is the device that tells the Ignition Coil when to do its thing and make the spark plugs fire.
It takes information from a device inside the distributor, the PIP (Profile Ignition Pickup) sensor and the PCM (Powertrain Control Module, AKA the Computer) to be able tell the Ignition Coil when to fire.

This PIP sensor has a bigger chance of being your problem than the ICM Module (TFI). After they moved the ICM (TFI) from the distributor to the fender they do not have many problems with it any more.

The ICM.


The PIP Sensor is inside of device below and this device, the Stator is inside the distributor.


Location of the ICM (TFI).

 

Not to take over here, but Subford, can you just replace the PIP sensor? I bought a whole brand new dizzy for my truck, with the PIP already in it! D*mnit!

 

Yes you can buy the Stator with the PIP sensor inside it and then put the Stator inside the distributor.
Here is a link to some at Advance.
http://www.partsamerica.com/ProductL...ickup%2fStator

 

Where could I have gotten that? I paid $100 for a new dizzy!

 

About $22.44, look at the link above.
But you still have take out the distributor to press off the gear and take the shaft out.

 

I pulled the dizzy and couldn't figure out exactly how to get it all apart, so I just bought a new dizzy with the PIP in it. Oh well!