Black vs Grey TFI Module ???

I would stick with Motorcraft. The Wells brand was sold by Autozone in the past.

2.3 - Push Start versus Computer Controlled Dwell TFI-IV ICMs

The internal circuitry of the TFI-IV ICM will have two possible arrangements; push start (PS) or computer controlled dwell (CCD).

The push start system allows for increased dwell (coil on time) when starting the engine. After engine start, the ICM internally determines coil on time (dwell) based on engine rpm (derived from the PIP signal), previous spark position and, coil charge time. The PCM calculates spark timing and outputs a rising edge of SPOUT at the appropriate time. The ICM turns the coil off whenever it sees a rising edge of SPOUT. The SPOUT signal is an acronym for SPark OUTput, a digital signal generated by the PCM. The falling edge of SPOUT is ignored by the ICM. On a push start system, SPOUT only controls when the coil fires. The dwell was designed to provide either 17% or 32% excess dwell to ensure sufficient coil charge time under transient engine-acceleration conditions. Push start TFI-IV ICMs are gray in color.

A computer controlled dwell (CCD) system uses both edges of the SPOUT signal. The PCM calculates spark timing and outputs a rising edge of SPOUT at the appropriate time. The ICM turns the coil off whenever it sees a rising edge of SPOUT. The falling edge of SPOUT is used by the ICM to turn the coil on. The coil on time (dwell), is therefore, entirely controlled by the PCM-generated SPOUT signal. The ICM does not internally determine dwell, it just responds to directly to SPOUT signal it receives. The PCM determined the correct dwell by measuring the time it takes for the coil to reach a predetermined current level. This has the advantage of limiting excess dwell, which significantly reduces heating in the ICM. TFI-IV ICMs that utilize computer-controlled dwell are black in color.

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http://megasquirt.sourceforge.net/extra/doc/ford-Ignition-tfi-edit.doc
There is your difference between black and gray modules. To the best of my knowledge, it's supposed to be gray. That's what I have on mine.

Agreed. Grey should have been the OEM color.

Most technicians who deal with Ford drivability and no-start problems have become very familiar with the Thick Film Ignition (TFI) system. Ford started using the six-pin TFI module with the EEC-IV computer system in 1983, and for years it remained basically unchanged.

The early TFI system, which Ford calls the "Push Start" TFI system, uses a gray TFI module. Originally, the module was mounted on the distributor. In the late '80s, Ford began to relocate it away from the distributor on some vehicles to provide better protection from the effects of engine heat, but system operation remained the same. It uses a Hall effect pickup (stator) in the distributor, which generates a battery voltage, 50% duty cycle square wave, called the PIP signal, to the EEC-IV PCM and the TFI module. The PCM processes this signal and sends out another battery voltage, 50% duty cycle square wave, called the SPOUT signal, to the TFI module. As long as the TFI module is receiving a SPOUT signal, it will fire the coil at the rising edge of that signal (except during engine cranking, when SPOUT is ignored) and the vehicle will run with the amount of timing advance commanded by the computer. If the TFI module does not receive the SPOUT signal, it will fire the coil at the rising edge of the PIP signal, and the vehicle will run at base timing. This is true on all TFI systems.

Ignition dwell with the Push Start (gray module) system is controlled by the TFI module alone, and increases with engine rpm. The Ignition Diagnostic Monitor (IDM) signal on a Push Start TFI system comes from the coil negative circuit and is filtered through a 22k ohm resistor to pin #4 on the EEC-IV computer. The computer monitors this circuit to verify a coil firing for each PIP signal, and sets codes if it sees missing or erratic signals. Another feature that is unique to the Push Start TFI system is the start input on pin #4 of the module connector. This is wired into the starter relay trigger circuit, and signals the TFI module that the engine is cranking. When the module sees battery voltage on this circuit, the SPOUT signal is ignored.

In the early '90s, Ford began using a different TFI system on certain vehicles -- the Computer Controlled Dwell (CCD) TFI system. The TFI module on CCD TFI is always black in color. There are a few major differences between the two systems. As the name implies, with the CCD system, the computer controls primary dwell. The CCD TFI module still ungrounds (fires) the coil at the rising edge of the SPOUT signal, but now the falling edge of the SPOUT signal (which had no meaning to the Push Start TFI module) is used by the CCD TFI module to ground the coil. The PIP signal remains the same 50% duty cycle square wave, but SPOUT signal duty cycle varies according to how much dwell is desired by the computer.

Another major difference between the two systems is the IDM circuit. Pin #4 on the CCD TFI module, which was the start circuit input on the Push Start TFI module, is now the IDM signal, sent directly from the TFI module to pin #4 on the EEC-IV computer. This signal is still a filtered (low voltage) version of the ignition primary waveform, but is filtered internally in the TFI module rather than through an external resistor. There isn't any start circuit input to the CCD TFI module; the module infers engine cranking from a low rpm input from the PIP signal.
Since these two TFI systems are so significantly different, yet so similar in appearance, parts application problems will inevitably occur. A gray Push Start TFI module will plug right into a CCD system, and vice versa. To make matters worse, parts books are often incorrect on TFI module applications! With the incorrect TFI module installed, the vehicle will run, but drivability and MIL (malfunction indicator lamp) problems will result. For instance, if a gray Push Start TFI module is installed in a CCD system, the computer will not be able to control ignition dwell, and the MIL will illuminate with memory codes for the IDM circuit set, as the gray TFI module is incapable of generating an IDM signal to the computer. If a black CCD TFI module is installed in a Push Start system, dwell will remain fixed, since the SPOUT signal duty cycle never changes. If in doubt about which TFI module belongs on a particular vehicle, consult the ignition system-wiring diagram for the vehicle. If the wire going to pin #4 on the EEC-IV computer comes directly from pin #4 of the TFI module, it is a CCD system. If not, it is a Push Start system.

To tell you the truth, I did not go back and check this against my wiring diagrams as they were done many years ago. I took diagrams from a well known book and color coded them as well as taking some from websites like Autozone.

The last two sentances in the above write up say it all - you use the module that the car is wired for. Most have no problem with a mixup as they buy the same color as was on the distributor to start with - but that assumes it's all untouched factory wiring - something that a 4 cyl conversion or other transplant may not be.

I will take a look at the 88-91 diagram as intuitively, you'd expact that to be a gray module - my 88 is. Keep something else in mind - I have made some corrections to the diagrams and my stuff is so widely used and shared, it's hard to know if you have the latest diagram.

I can't tell you that from cyberspace - it depends on what came in the car originally and how it is wired - see above for what to check.

All Fox Mustangs (manual and auto transmissions) are the Push-Start TFI module type. Both have the "start" voltage input to the TFI module as shown in the extract diagram below. I know there are different TFI (still trying to ID what's the difference) part numbers for auto and manual transmission fox Mustangs, but it's not until 1994, with the SN95's, that CCD TFI is "added" for both transmission types.

90topdown said:

Update- Came back home and pulled codes. Got a code 96 (secondary fuel pump circuit failure)

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Your problem is with the relay power circuit (edit: primary) instead of the power to the coil (edit: secondary). The power goes through the inertia switch to the relay coil and then back to the computer on terminal #22 on the EEC where the computer grounds the circuit to run the pump. I'd guess you're loosing voltage to the :edit: pump somehow - weak connection possibly or somewhere else. Could be the wiring between the coil and computer too.

.... a little correction, if I may........ code 96 - Fuel Pump Circuit Open-Battery To PCM (M,O) or secondary circuit, which is the power switching side at the relay from the battery to the fuel pump, to the FPM pin at the ECM. It means that during a period of time, the voltage output sensed by the FPM pin is too low/open. Need to check voltage from the fusible link at the starter solenoid-to-FP relay-to-fuel pump/FPM pin 19 at the ECM. LUK

Joel, I didn't follow that so well - have I been wrong in saying the secondary is the coil and the primary the power to the pump? Backwards?

At any rate, you can see that the EEC does monitor EEC power at EEC pin #37. Pin #19 is the power circuit to the pump that is monitored too.

tmoss said:

Joel, I didn't follow that so well - have I been wrong in saying the secondary is the coil and the primary the power to the pump? Backwards?

At any rate, you can see that the EEC does monitor EEC power at EEC pin #37. Pin #19 is the power circuit to the pump that is monitored too.

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Yep.... primary is coil and secondary is power switching side in the relay. That is another (pin 37) reference point to compare to pin 19's input the system uses.

Got some low voltage problem there...... 10 vdc at the fuse link is too low. The "threshold" for the ECM is 10.5 vdc at pin 19, but the supply is below the normal 12 vdc expected. May want to check those main grounds (block and b-to-frame)..... LUK