TFI Distributor Shutter Wheel


The Truth About TFI Ignition, And Aftermarket TFI Distributors

The Ford TFI ignition system may best be known for the troublesome TFI module that would fail when it got hot. The engine would run for about half an hour, the TFI module would fail, and you’d be stuck on the side of the road. After some time to cool off, the engine would start back up, and you’d be on your way, but once it warmed back up again, you were again stuck on the side of the road. 

It’s truly a shame that this is how TFI will be remembered. The truth is that the TFI ignition system was actually pretty ingenious. Yes, there were issues, but Ford did address them, and today a TFI system built with genuine Ford parts is actually a very good and very reliable ignition system. 

The ingenious part of the Ford TFI system was that it allowed you to use the distributor as a camshaft and crankshaft position sensor, which allowed the ECU to fire the fuel injectors sequentially. Today, we actually use this same principal to fire multiple coils sequentially, which provides for a very simple, yet very effective way to adapt multiple coils systems to older engines that were not originally equipped with multiple coils. The way the TFI system works is pretty simple. There is a toothed wheel (the Shutter Wheel) mounted to the distributor shaft. The wheel has eight teeth (one for each cylinder), one of which is narrower than the other seven. The narrow tooth represents cylinder number one. These teeth pass through a hall effect sensor. The sensor sends a signal to the TFI module, which in turn fires the coil. The ECU monitors the square wave pattern created by the shutter and hall sensor, and uses this to determine engine position and RPM. Simple...

The real trouble started when the aftermarket got involved. Aftermarket companies started making replacement hall sensors and TFI modules. The hall sensors are absolute garbage. The TFI modules are not much better. If you buy a hall sensor from the parts store, you’ve got a very good chance it will not work right out of the box. The ones that do work will likely fail. It’s just a matter of when. They often fail when they get hot, and then start to work again when they cool, much like the old TFI modules. Because of this, people will often misdiagnose the problem, and replace the TFI module, only to find later that they are stuck on the side of the road again. Even the ones that do work often produce such a poor quality signal that it is difficult for the ECU to properly determine engine position. 

Then the aftermarket started building replacement performance TFI distributors. While pretty to look at, these distributors actually represent a few steps backwards:

(1) They use the aftermarket hall sensors. The good news is that you can still buy an original Ford hall sensor and install it in any of the aftermarket distributors.

(2) They use the aftermarket TFI modules. 

(3) The shutter wheels they manufacture are NOWHERE NEAR the quality of the originals. The original Ford shutter was held to a tolerance of one half of one degree. The aftermarket ones are so bad, you can often see the difference in the width of the teeth with the naked eye! The result of this will be an inconsistent spark advance from cylinder to cylinder. 

(4) They do not mark the distributor cap with the location for the number 1 spark plug wire. This will almost certainly result in a distributor that is not properly phased to the engine, resulting in incorrect fuel injector sequencing. 

These distributors DO NOT OFFER ANY INCREASE IN PERFORMANCE whatsoever. And now that you understand how TFI works, you understand why. They have not changed a thing that would do anything to improve performance. In fact, the poor quality components actually reduce performance due to the inconsistent spark advance! A better coil, increased primary voltage, and longer dwell times (the length of time the coil is charged) are the only ways to increase the output potential of your ignition system. These distributors do none of these things. 

Some of these manufacturers claim that their TFI modules provide increased dwell times, and therefor produce a hotter spark. This is not possible:

(1) Every coil has an optimum dwell time at a given system voltage. When they sell you a TFI module, they do not know what coil you are using, and therefor do not know what that dwell time is, unless they sold you a coil too, however….

(2) Even if they do know what the optimum dwell is, there is not enough time between cylinder events to dwell the coil long enough to reach those dwell times! At least not with a single coil system, which is where multiple coil systems come in. More coils means more available dwell time, and a real increase in performance.

So what did we learn?

(1) If you want a better ignition system, buy a Coil On Plug system. Yes, you can use a CD box, but those are as unreliable as the aftermarket distributors. Learn about our C.O.P.

(2) If you own one of these aftermarket distributors, you probably have a junk hall sensor. Buy a new one from the Ford dealer and install it. 

(3) If you have one of these aftermarket distributors, you likely have a junk shutter wheel. It is very easy to determine if yours is good or not. The proper tooth dimensions are below. Measure your teeth with a dial caliper or micrometer. If the dimensions are wrong, then change it. New ones are available from Pro-M Racing on this page. 

Proper shutter wheel tooth dimensions for a V8 shutter wheel:

Large teeth — .398 to .400

Small tooth — .258 to .262

There should also be even spacing between the teeth, with the exception of the long space following the narrow tooth. 

We should mention here that our Pro-M EFI engine management system employs a strategy to deal with the bad shutter wheels. Our strategy averages out the pulses generated by the shutter passing through the hall sensor. This provides a consistent spark at all cylinders. The Pro-M EFI system will also set a diagnostic code if the shutter or hall sensor is so bad that the ECU cannot make sense of the signal. Just one more feature of the advanced diagnostics in the Pro-M EFI PCM.

The Pro-M EFI Powertrain Management system is a Mass Air, sequentially fired, port fuel injection system, with full ignition control, and transmission controls, as well as a host of other features listed below. The Pro-M EFI system provides a combination of drivability and quality typically only found in the OEM, combined with a level of performance typically only found in the aftermarket. It is truly the best of both worlds. All provided in a package so easy to use, most anyone can become their own tuner.

The Pro-M EFI Engine Management System for 1979 - 1985 Fox Body Mustangs includes our fully programmable Pro-M EFI PCM, tuning software and a custom Mustang powertrain wiring harness. Your New Pro-M EFI wiring harness will be made to fit your specific model year Mustang. It is not a universal harness. It installs in the car just as if it had been made by the factory, and uses all the same sensors, connectors and circuits as the OEM harness. We have several different wiring harness configurations made specifically for all Mustangs produced from 1979 through 2004. The harness can also be used as part of one of our complete EFI conversion packages.  You can read about our complete EFI conversion kits here.

The new Pro-M EFI PCM will be shipped with the “tune” pre-installed. The customer need only enter some basic information about their specific application. These parameters can also be entered here at Pro-M for an additional fee if the customer desires. This tune will run virtually any engine right out of the box. Tuning is neither required, nor is it recommended. The money you will save by not going to the tuning shop will actually pay for your Pro-M EFI system.  No one else can make this claim.

We will also include a software package that will allow you to make nearly any modification to your powertrain you could ever want and do so with amazing simplicity. The Pro-M EFI system can be as simplistic, or as sophisticated as the user wants it to be. Tune if you want to or leave it alone if you don't. Everything you could ever want in a management system is right here!


Features of the new Pro-M EFI system include:

The Pro-M EFI Powertrain Management system is a Mass Air, sequentially fired, port fuel injection system, with full ignition control, and transmission controls, as well as a host of other features listed below.

Water and shock proof OEM quality PCM. Made side by side with the OEM's. No one else does this!

OEM quality wiring harness. Installs exactly like the original harness, using all the same connectors.

Fully laptop programmable. Tune because you want to, not because you need to. Your laptop also acts as a powerful scan tool.

New improved calibration tool with multiple user levels. Tuning software so easy and intuitive, most anyone can be a tuner. Now compatible with both PC and Apple!

Store an unlimited number of tunes. 

Tune on the fly and see the results immediately.

OBD II compatible. Not only does your laptop act as a powerful scan tool, you may also read codes and sensor data using a generic OBD II scan tool. The Pro-M EFI PCM uses the same code strategy and the same codes that all the OEM's use!

Automatic transmission controls for AODE/4R70W/4R70E/4R75W/4R75E

Manual shift option. Use your cruise control buttons (94-2004 Mustangs), or your own switches to manually shift your automatic transmission!

Flex Fuel. Done the right way! Easily make big power on E85!

Traction control. Intergraded into the PCM! No parts to buy!

Launch assist.

Boost control for both turbocharged and supercharged applications.

Fully programmable progressive nitrous controls. No external controller needed!

Fully programmable progressive water/methanol injection controls. Done the right way. No external controller needed. Advanced OBD II diagnostics and fail-safe features make this absolutely the best water/methanol control system in the business.

Individual cylinder tuning.

Advanced timing control that actually rivals the accuracy and consistency of “Coil On Plug” high data rate ignition systems, while still using your distributor.

Optional “Coil On Plug” ignition system. Worlds better than a CD box!  Read More . . . 

Supports OEM “Coil Pack” and “Coil on Plug” ignition systems. If the engine you want to run was originally equipped with “Coil Pack” or “Coil On Plug” ignition, we can run those too!

Ignition module problems are a thing of the past! The ignition module is integrated into the Pro-M EFI PCM. No more failed TFI Modules.

Able to run two Mass Air Meters simultaneously. No limit to the amount of power you can make!

Easy, user adjustable two stage Rev Limiter. Cut fuel or spark or both.

No Lift Shift with rev matching with each gear.

T-56 Reverse lockout control.

Adaptive fuel control.

Adaptive idle controls.

Fuel pressure compensation.

Fuel pressure warning.

Electric cooling fan control with Soft Start feature.

Cooling fan cool down feature.

User programmable outputs.

“Decel Fuel” feature cuts fuel while decelerating. Saves fuel!

Operates in continuous closed loop with TWO wide band oxygen sensors (not one sensor like the other guys), which adjust each bank independently, resulting in the most precise control over air/fuel ratio in the industry.

No special tuning required for forced induction. Our “Load” based system makes forced induction super easy.

Advanced data logging feature built into the software.

Automatic updates for the calibration tool and user manuals.

Self-protecting PCM. The Pro-M EFI PCM detects short circuits and will shut down that PCM driver if a short is detected.

We cannot stress this enough...The real beauty of the Pro-M EFI system is that it can be as simplistic, or as sophisticated as you want it to be. It works perfectly right out of the box with some simple data entry, but if you want to tune, you'll have the most powerful tuning software ever offered anywhere by anyone, and OEM quality components that will last a lifetime. 

If you want the best, look no further. There is simply no other management system that offers the quality, features, reliability, and ease of use that we offer with the Pro-M EFI engine management system, period...

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