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Fox Body Computer Chips - Facts & Fundamentals

By:  Connor MC  / May 30 2019
Fox Body Computer Chips - Facts & Fundamentals

A Fox Body's computer restricts the amount of power your engine can push. An aftermarket chip and tune will go a long way lifting the stock computer's limitations.

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The overall performance of your Mustang depends on a quality tune, whether you are building a track monster or restoring a stock Fox back to its original glory. Ensure your car is running at peak performance with a custom chip and Bama tune.

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Facts About Fox Body Computer Chips 

  • The engine control unit (ECU) is designed and programmed to run the car under all conditions
  • Aftermarket chips and tunes are keys to achieving maximum performance from your Mustang
  • Chips and tunes are specifically designed for your engine combination
  • Chips and tunes become necessary when you modify your Mustang’s engine through heads, intake, and cam swap

What is a Mustang's ECU, and What Does it do?

Quick and dirty, ECU is short for ‘engine control unit’ (also called ECM and PCM – short for engine control module and powertrain control module). Essentially, it's a computer module designed and programmed to run the car under all conditions at maximum efficiency. Some tasks of the computer are:

  • Control fuel delivery (right amount at right time)
  • Control spark timing
  • Exhaust gas circulation and oxygen content

All of these parameters are monitored by 22 different sensors placed throughout the engine. Disregarding all of this technical jargon, a car’s computer is really like a central brain. It will control how the car operates at idle, under load, and at wide open throttle. The reason cars are so reliable under all conditions nowadays is because of the use of these engine control units.

Fuelab Mustang Fuel Pump

Your Fox Body Mustang's Computer

The specific unit Ford developed and used in their Fox Body Mustang was the EEC-IV computer. Composed of a 16-bit microprocessor running at 15 mHz and 16 kilobytes of read-only memory (ROM), the EEC-IV was still capable of processing over 1 million calculations per second!

The EEC-IV computer debuted in the Ford Mustang in 1983. Running all the way until 1993, the stock EEC-IV ECU is actually a very versatile and competent system. The stocker actually does a very good job at adjusting for many different modifications. However, the stock EEC-IV does leave a little power behind – it is, after all a factory piece and therefore optimized for greater efficiency, reliability, and emissions control (basically it's conservative).

Two-Tone Fox Body Mustang

Tuning Your Mustang for Maximum Performance

The fix for this is to go with an aftermarket chip and tune. The benefit of running an aftermarket chip and tune is they are designed specifically for your engine combination, optimizing all the parameters necessary to run the engine at its best for its intended use (be it street, track, or a combination of both – small changes here and there can produce an entirely different monster). Before dwelling deeper, let us first examine the stock computer. As stated, it's a stout system and changes are unnecessary until a certain point.

Fox Body Mustang Tuning Chip

Mustang Speed Density Systems vs. Mass Air Systems

The EEC-IV computer works in conjunction with another type of engine control system, depending on the year of the car. 1987-1988 Mustang (excluding 1988 Mustangs sold in California) came equipped with a speed density system. Mustangs 1989 and on came installed with a mass air system (still used today). The difference between these systems is the way they measure incoming air. The speed density system is actually a ‘dumb’ system – it does not actually measure the air. Rather it uses a formula and a premade table of values. A mass air system does measure the incoming airflow, and the EEC-IV makes the corresponding adjustments based on the live measurements. In terms of performance, a speed density car is said to be quicker when both are stock. However speed density systems are not as modification friendly (particularly with camshaft changes). For this reason, it's highly recommended you convert to a mass air system when you begin modifications.

Fox Body Mass Air Flow Meter
Mass Air Meter

When to Consider Getting a Chip and Tune

As already stated, the stock ECU is quite good at adapting to basic mods. However, from the factory Ford designed their vehicles for the emissions conscious states and individuals. Installing a chip and custom tune will show horsepower and torque gains on even a stock Fox Body. Basic changes like exhaust, throttle body, or the addition of a cold air intake, will be better accounted for by the computer and work more efficiently together as a system. A chip really becomes useful when the engine is revamped via heads, intake, and a cam swap. That is where you will notice the greatest power, efficiency, and overall driveability gains. Some of these engine mods cannot successfully be completed without a chip and tune!

5.0 Fox Body Mustang with Ford Racing Heads

What Performance Mustang Chip Will Get the Job Done?

A very popular (and actually economical) chip to tie your top-end mods together is the SCT 4-bank Eliminator chip. This chip plugs right into the J3 port of the stock EEC-IV ECU (located underneath the passenger side kick panel) and comes with free tunes for life from Bama Performance. Perhaps the best feature about a chip setup like this is you can switch tunes instantly using a switch. The chip will store several tunes, and they can be accessed and run instantly via flipping a switch rather than having to connect a laptop each time and transfer over a different tune.

Standalone ECUs and Tuning

Another option, albeit a more pricey one, is to go with a standalone ECU tuning setup. A standalone ECU replaces the factory ECU with one that can control a wider set of parameters. The name aptly describes what it does, it stands alone from the factory ECU, controlling everything the factory ECU does and more. Standalone systems allow you greater levels of customization and control when it comes to tuning your vehicle, essentially giving you the power to tune your car from scratch, dialing in your engine's parameters to your precise liking.

So, if a transmission has a stand alone ECU, it will not shift based off of the stock ECU's input. The transmission would have its own computer system. This can be beneficial in instances where the stock ECU can not supply the necessary computations for the transmission. Additionally, stand alone units can handle more power and precision when it comes to tuning and aftermarket applications. They are especially useful in not stock applications, where a stock ECU has a transmission attached to it from a different model (IE: Coyote and 4r70w).

In all honesty, unless you have a HIGHLY modified Mustang (talking body panels that have been replaced with lighter fiberglass or other materials), tubed chassis, aftermarket crate motor, boost, and everything in between) that is strictly competition use, then standalone tuning doesn't make sense from a practicality or financial standpoint.

SCT 4-Bank Eliminator Chip
SCT 4-Bank Eliminator Chip

How Do I Get My Tunes?

You simply send in exactly what parts and specifications are used in your car. Bama has dialed in nearly every combination of mods and will create three custom tunes specifically for your car. A service just as good as strapping the car to a dyno and at a fraction of the cost over the life of the vehicle makes Bama the top tuning service for Mustangs worldwide.

No doubt about it, if you are seeking to really tie your engine combination together, perfect power and torque, better efficiency and ultimate driveability, consider using a 4-bank SCT Eliminator chip. Instalation is fast and painless (plugs right in to the stock EEC-IV J3 port). With the accompanying Bama Performance tunes, at the flip of a switch you can have a tame street driver or an all out performance machine. For many, a chip and tune is the best bang-for-your-buck purchase you can make.

Bama Custom Tunes Logo

How Mustang Chips Help You Dial In

The chip will allow for the calibration of injectors. Ford and SCT (the more common MAFs) do not take injector size into calibration. It has been known for the mass air flow sensors 'calibrated' to a certain injector size to be incorrect and not run properly. A chip would allow for the correction of injector size, along with idle rpm, spark and fuel tables, redlines, speed governor, etc.

Fitment includes: 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, GT, Cobra, LX, SVO