Troubleshooting a Ford Ignition Module

by Don Bowman

Introduction

Ford used the TFI ignition module (thick film ignition) on vehicles from 1983 through the mid-1990s only. The vehicles that used this module had a conventional hall-effect distributor with a separate coil. The TFI module was located on a flat area on the base of the distributor. On some trucks and cars in the 1990s, the module was located on the radiator support housing within a heat sink. It contains solid state components encased in a thick clear electrolytic film. Its primary purpose is to send the hall-effect signal indicating top dead center on the number one cylinder to the electronic engine control (EEC-IV). The computer then takes the signal and the pulse rate and determines the rpm. The computer sends a signal to the control module when to fire the coil. The control module automatically controls the dwell for sufficient saturation of the coil windings to give the proper spark duration given the rpm in real time without creating undue heat. It also monitors irregular or missed firing counts and will set a code if a failure is imminent. However, this does not always work properly. There have been many problems with this system, stemming from heat saturation, cracking and a myriad of problems after a period of service.

Failure

The modules will fail once they have absorbed too much heat or for case problems. When this happens the vehicle will stall and take a period of time for a successful restart after the heat has dissipated. It can also cause a bad miss on an erratic basis.

Diagnosing the Module

If ignition problems are experienced, the first thing to do is to install a timing light and watch for an irregular spark. If there is, check the plugs. If the plugs are alright, the module should be replaced. They are not expensive, however, they require a small special tool to remove the torx screws in the module housing. If there was no misfire, but the vehicle is hard to start or stalls, the module should be inspected and replaced if found to be faulty. The module should be removed and checked for cracking around the torx screw mounting surface. There should be a thick film of dielectric grease on the back metal side of the module. This layer of grease keeps the heat off of the module. If the module looks OK but the grease is depleted, it should be replaced and the module can be tried again by using the timing light for steady spark. The PIP signal should also be checked. The top wire on the connector is used to check for PIP. Use a voltmeter and look for pulsing with the engine running. The pulsing means the wire from the computer to the ignition control module is good and the computer is working. If it is working, the module is bad. If no pulsing is noted, check the third terminal down for pulses to the computer. It would be wise to replace these modules every 30,000 miles as a preventative maintenance procedure considering the amount of failures and the relatively low cost versus the aggravation should a failure occur. The modules have never been modified so the new will only last as long as the old one.

About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).