Ford EEC-IV Engine Control

Since my main interest lies in computers (and has since I was really young), and I drive the Pintomobile, I think it would be interesting to take a look at the EEC-IV "engine computer" which powers the Ford 302 engine in the Pintomobile. For early engine controls, and early electronic fuel injection, it is fairly interesting and complex.

What is the EEC (or an ECU?)

An ECU/MCU (Engine/Motor Control Unit) is the "brains" behind the engine in most automobiles manufactured during or after the mid-late 1980s. Ford started putting EEC modules in all of their cars, regardless of featuring EFI or not, since 1984 with the introduction of the EEC-IV. An ECU provides major advantages over not having any type of engine control unit. These advantages include:

A History of EEC (plus the future)

While Ford calls their "engine computers" by the name EEC (Electronic Engine Control), the generic term is ECU or MCU (Engine/Motor Control Unit.) The EEC was the first type of mass-produced engine computer used in automobiles.

The first EEC and the EEC-II were both based on the PDP-11 computer. The original EEC modules were based off a 12-bit microprocessor made by Toshiba, and was based on the PDP-11 as earlier the PDP-11 was used in automobiles as "proof of concept." However, the EEC and EEC-II were only used on performance cars, and were not typically found in mass-produced cars. (You wouldn't find it in your run-of-the-mill Ford Taurus or Ford Pinto at the time.)

Other manufacturers, such as GM (with the CCC, or "Computer Command Control") and AMC, followed Ford's lead and produced their own ECU modules. The AMC CEC (Computerized Engine Control) used on AMC and Jeep vehicles were made by Ford for AMC (American Motors Corporation) from 1980 to 1990. The CEC and EEC modules have no relation other than being designed and manufactured by Ford.

General Motors was the first company to implement computerized engine control in all of their vehicles, beginning in 1981 with the CCC. This system was a "morphodite" system.


The EEC-III was more widely used by Ford, but still only used on certain models between 1981 and 1983. The EEC-III and the original EEC modules both were designed to work with carburetors. Prior to EFI (Electronic Fuel Injection), carburetors were the mechanisms used to mix the air and fuel. A proper fuel-air ratio is required for proper combustion, and proper performance of any engine. The EEC-III and prior EEC modules were connected to a "cam" located near the carburetor. This cam would rotate, therefore changing the fuel/air mixture inside the engine. Prior engines, before ECUs, used a linkage between the accelerator (throttle) and the carburetor to adjust the fuel/air mixture.

The EEC-III also could be utilized with fuel injection; central fuel injection. The EEC-III utilized the infamous Motorola 68000 microprocessor (the same one used in the original Macintosh, and various other home computers) to power it.

The EEC-III also utilized the Dura-Spark ignition module, as well as the EEC-II and original EEC using the same ignition module.


EEC-IV was the fourth generation of Ford's EEC. By this time, it was well known that computers would take over inside of cars, and the EEC-IV further advanced that notion. The EEC-IV was released in 1983, although work began before EEC-III began being produced. The EEC-IV was produced from 1983 until 1997. Starting in 1984, the EEC-IV was placed into all vehicles produced by Ford, including those featuring carburetors. By the end of the EEC-IV's life cycle, all cars would feature EFI, which was only a luxury in 1983.

Due to the long life of EEC-IV, there was multiple incarnations of it made by Ford. In 1983, Ford relied on through-hole componentry to make up the EEC-IV. By 1997, the EEC-IV was almost entirely made of surface-mount technology (SMT) parts, which allowed it to be much smaller, without lacking power. The EEC-IV featured KOEO (Key On, Engine Off) and KOER (Key On, Engine Running) self-tests, the first ECU to do so. (Almost all, if not all, ECU modules have these self-tests today.) The EEC-IV also featured a KAM (Keep-Alive Memory), which allowed it to store codes and other important data, even if main power is lost.


The EEC-V is the fifth ECU made by Ford, and the last to use an Intel processor. The ECU's produced by Ford after the EEC-V were all based on PowerPC processors. The EEC-V was essentially an extension of the EEC-IV family, as it carried over much the same code used by the EEC-IV. The EEC-V was based on the Intel 8065 (MCS-65) microprocessor.

Inside the EEC-IV

When the EEC-IV was introduced, almost all cars were still based around the mechanical carburetor design, where a linkage between the throttle pedal and the carburetor controlled the fuel/air mixture. Also, at the time the EEC-IV was introduced, cars also relied on distributor caps for timing. Distributors were unreliable, as they were based around a fast-rotating cam which spun a rotor. This rotor, which spun at the same revolution as the engine, would make quick contacts with the "points" inside of the distributor cap. This would send the high-voltage spark to the particular spark plug, thus firing the engine. However, this design was prone to wearing out over time, and misfires (where a cylinder does not fire all of the time, or only fires some of the time) were the result.

The EEC-IV would not eliminate all of these issues immediately, but would eventually over time. By 1990, most Ford vehicles utilized EFI (Electronic Fuel Injection.) The EEC-IV was the brains behind the EFI used in these vehicles. During its lifespan, vehicles using the EEC-IV module as an ECU would still rely on distributors for timing, but in 1997, with the EEC-V, the ECU also took control over the engine timing.

The EEC-IV used TFI/TFI-IV (Thick Film Integrated Ignition)for ignition. The TFI module is typically either located on the distributor, or in the engine compartment on a heat sink. The TFI is prone to heat damage, and can be replaced.

The EEC-IV is based on the Intel 8061 microprocessor. The 8061 (or MCS-61) is a close relative to the later 8096 (MCS-96), both of which share most of the same instruction set and layout. However, the 8061 has some features which make it more suitable for ECU use, such as the ability for use in higher temperature environments among other things, as well as some important additional instructions for use with the high-speed I/O. Ford developed the 8061 with Intel, but later the design was manufactured for Ford by Motorola and Toshiba. The 8061 was eventually produced alongside the 8065 in the late 1990s, but the 8096, the well-known cousin of the 8061, did not die until 2007. The 8096 found use in many consumer products, such as modems, motor controllers, other ECU modules, and even photocopiers and general electronics.

Despite the EEC-III being produced by Ford, Motorola, and Toshiba, Intel only produced the microprocessor inside the EEC-IV. Later, the 8061 was second-sourced by Motorola and Toshiba.

Intel 8061

The 8061, similar to the 8096, feature HSI (High-Speed Input) and HSO (High Speed Output) systems. These make it more suitable for use in automobiles. The HSI was used in many different applications, but an example is determining engine speed by recording the times of the position of the crankshaft.

The 8061 has a 240-byte large internal register file, which could address from 0010H to 00FFH. Typically, the stack pointer was located at 00010H. The 8061 could address up to 64k of RAM.

There were various physically different packages the 8061 was offered in. There was a 68-pin square flat pack, and a 40-pin DIP. The 68-pin features additional I/O.


The EEC-IV uses a custom EPROM and RAM. This EPROM stores the standard programs executed by the EEC-IV. The program code (typically stored in either C or Assembly) stored in the EPROM can be read, but the data can be damaged if care is not exercised while reading. (Since it is a standard EPROM, regular sunlight or fluorescent light sources can erase the data stored in the EPROM.)

Later EEC-IV modules, specifically those designed for use with antilock brake systems, used fuzzy logic with antilock brake systems. For instance, my 1989 Ford F150 XLT Lariat (Pintomobile) uses fuzzy logic to control the rear antilock brake system.

The EEC-IV performs all simple tasks required to efficiently run the engine, such as quickly but accurately calculating fuel/air mixtures and emission outputs. The EEC-IV also constantly monitors all systems, especially through sensors in the engine, transmission (with cars equipped with electronically-controled transmissions, the Pintomobile still relies on hydraulic means to control the transmission), and exhaust system. Any failures or potential failures, such as continious mis-firing, will result in the EEC-IV producing a code which is stored in memory for future use. (See the below section for diagnostics.)

There are different types of the EEC-IV which is programmed to match a specific Ford engine. Each type of module contains a different fuel/air mixture ratio which is specific for the engine and anciliary devices it is matched with.


The EEC-IV offers OBD-I diagnostics, and the codes are stored inside the EEC via KAM. KAM (Keep-Alive Memory) will ensure the codes are not erased if main power is low, although removing power altogether (disconnecting the battery completely) will completely erase any diagnostic codes stored in the EEC-IV module once the internal capacitors have completely discharged. The KAM is composed of a separate wire running to the battery, and the KAM consumes low power. The KAM EEPROM is 128 bytes large.

The EEC-IV has two modes of self-testing. These self-tests are found in almost any ECU after or during the mid-late 1980s, and are found in almost all (if not all) ECU modules produced today. These diagnostic self-tests are KOEO (Key On, Engine Off) and KOER (Key On, Engine Running). It is normal for your "Check Engine" light to illuminate while the key is in the "ON" position, but the engine is NOT running. (This means the ECU is operating normally.)

The diagnostic codes can be pulled by a dealer or auto-parts store using an OBD-I code reader. The diagnostic port is located under the hood. On the Pintomobile, a 1989 Ford F-150, the OBD-I port was located above the front driver side wheel well. It is a grey connector with it not connected to anything, although it may be hiding under a black plastic cover (this black plastic cover likes to fall off over time. Mine has fallen off.) The EEC-IV module is located in different places in different cars. My 1989 Ford F-150 has the EEC-IV module located "in" the firewall on the driverside. (This area is often referred to as the "driver side kickpanel.")

Later ECUs use OBD-II, which typically has the port inside the cabin. OBD-II is much more advanced in comparison to OBD-I.

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Last updated 09/09/2017 ; T420 (Created 7-25-16)