Here are some pertinent excerpts from "EEC IV Inner Workings", by tmoss (Last Revised: 12/16/2002).
Diagnostics
Two types of diagnostics are present in the EEC, On-Demand and Continuous. On-Demand is conducted during key- on/engine-off and during engine running modes to allow the EEC to test itself. Continuous is on anytime the EEC is in operation. Conditions found during Continuous operation are stored in special memory called "Keep Alive Memory" (KAM), which is 128kb of read/write memory. KAM receives its power directly from the battery. If the car battery is disconnected, or if the battery voltage falls too low, the KAM is preserved capacitors internal to the EEC. Stored codes are very useful in determining potential trouble.
...
Fuel Control
The air temperature sensor, the engine temperature sensor, and the Oxygen Sensors (O2 or HEGO) are also used to help determine fuel and timing requirements. Both the MAF and SD systems use barometric compensation. ... In the MAF cars, the Barometric Absolute Pressure sensor measures barometric pressure directly and continuously.
...
The EEC does not control injector “on” time from just a *single table *. The EEC calculates this time by monitoring sensors, and calculating “on” time based upon fuel flow.
...
There are two methods of EEC fuel control, Open Loop and Closed Loop. The EEC starts in Open Loop and based upon time and engine parameters such as engine temperature, changes to Closed Loop. During Open loop operation, the O2 sensors are not used to trim air/fuel mixture and hence the name “open” loop. Closed Loop operation consists of an EEC controller that uses a target air/fuel ration contained in lookup tables (based on a Ford test engine) that uses the O2 sensors as feedback for making adjustments. If the output of the O2 (HEGO) sensors stay either below .33 volts or above .8 volts, then the engine is running too lean or too rich.
...
The EEC varies A/F ratios by varying the "pulse width" of the voltage applied to the injector solenoid. Pulse width is a term to describe how much average voltage is applied to an injector coil over a given time span - typically about 2.5 milliseconds for EFI cars. 12vdc is always applied to the injectors but when you average the applied voltage over a set time span, shorter pulses result in lower average voltage (leaner A/Fs) over that time period and vise-versa (richer A/Fs) for a given air flow quantity.
...
Anything external to the EEC, which that tries to modify the desired air/fuel ratio (based upon data from a Ford test engine – hence the name “base” Open Loop Fuel Table) in closed loop operation, will cause the computer’s Adaptive Control feature to try to compensate for the change by writing correction multipliers to KAM that correspond to the load level at which the out-of-tolerance value occurred. The Adaptive Control will also monitor how the engine is responding to the way you drive and make adjustments.
...
EEC Controls
The EEC sees only one crank position sensor signal, a short signal on the shutter wheel in the distributor shutter wheel. The Hall effect “pickup coil” as it is generally known has a magnetic field that is interrupted from the sensor by a wheel containing shutters that spin past the sensor. The signal output from the Hall effect sensor is called a Profile Ignition Pickup (PIP) signal. There is one shutter that is skinny and this is how the EEC knows the #1 piston top dead center position by its mechanical relationship through the timing chain and distributor gear. This is how the EEC knows where each cylinder is in the firing order due to monitoring the time rate between PIP signals (changing rpms) and the internal firing order data, which enables it to control sequentially the firing of the injectors.
...
The TFI module cleans up the PIP signal before sending it off to the EEC. The TFI also uses the Spark Output (SPOUT) signal, from the EEC, to determine when to fire each plug. The coil fires on the falling edge of the SPOUT signal. The TFI also provides an internal SPOUT signal (based on the PIP signal) for limp home mode operation if it senses the EEC has stopped sending the SPOUT. If the SPOUT plug is not inserted, spark timing remains at base timing during engine operation. The EEC controls the spark based upon lookup tables like the air/fuel mixture.
...
The computer interpolates (ratios) values for load and rpm between the table values so timing is adjusted for every cylinder firing. Once again the MAF signal and other sensors measure % load and a value of spark is chosen based upon engine rpm.
...
Adaptive Control
There is much confusion about how Adaptive Control works especially at WOT. Adaptive control, ... is always functional – at WOT and anything less than WOT. The difference is that in open loop and at less than WOT, this feature monitors O2 sensors and writes correction factors to KAM, which are applied to the table value Air/Fuel mixture injector pulse widths for future calculations. The rate at which Adaptive Control writes these correction factors to KAM is slow enough to filter out short duration upsets in the mixture. Short-term closed loop corrections are written to Long-Term Adaptive Strategy KAM if they repeat. At WOT the Adaptive Control still functions but it does not update (or write) correction factors to KAM for application to the base tables – it defaults to the already stored correction values, if any have been written, for the load and engine temperature experienced in the WOT load range.
...
Closed Loop
When the EEC reaches a point where it is satisfied with all monitored parameters, it will transition to closed loop operation. In this mode the EEC tries to control air/fuel mixture to the stoichiometric ratio of 14.7:1 and accomplishes this by adjusting injector pulse width with feedback from the O2 sensors to control to the 14.7:1 ratio.
...
EEC will not go into closed loop at a temperature less than 170°F.
...
If you place the HEGO O2 sensors farther away from the head than the stock location, you may have the sensor too far away to keep it hot enough to read correctly due to the cooled exhaust gases. This causes the EEC to enrich mixture and may cause plug fowling. Ceramic heat coating the headers will help maintain exhaust gas temperature. The EEC has a timing table used to time the sampling of the O2 sensors to coincide with the arrival of the latest cylinder exhaust pulse from each bank. Moving the HEGO sensor further away (or closer for that matter) may result in an ill-timed sample, which could also cause improper air/fuel mixtures to occur.
...
Another thing the '94 - '95 cars do with spark is retarding it during a shift. The automatic cars REALLY pull out the timing... Inside the ... EEC calibration is a thing called Tip-in Retard. Any time the throttle is moved from a more closed position to a more open position, it can pull out some timing.
...
The 94-95 automatic cars have a torque modulation strategy installed in them to vary spark during shifts. When the EEC thinks it's time to change gears, it can pull out massive amounts of timing so the shift is nice and smooth.
Diagnostics
Two types of diagnostics are present in the EEC, On-Demand and Continuous. On-Demand is conducted during key- on/engine-off and during engine running modes to allow the EEC to test itself. Continuous is on anytime the EEC is in operation. Conditions found during Continuous operation are stored in special memory called "Keep Alive Memory" (KAM), which is 128kb of read/write memory. KAM receives its power directly from the battery. If the car battery is disconnected, or if the battery voltage falls too low, the KAM is preserved capacitors internal to the EEC. Stored codes are very useful in determining potential trouble.
...
Fuel Control
The air temperature sensor, the engine temperature sensor, and the Oxygen Sensors (O2 or HEGO) are also used to help determine fuel and timing requirements. Both the MAF and SD systems use barometric compensation. ... In the MAF cars, the Barometric Absolute Pressure sensor measures barometric pressure directly and continuously.
...
The EEC does not control injector “on” time from just a *single table *. The EEC calculates this time by monitoring sensors, and calculating “on” time based upon fuel flow.
...
There are two methods of EEC fuel control, Open Loop and Closed Loop. The EEC starts in Open Loop and based upon time and engine parameters such as engine temperature, changes to Closed Loop. During Open loop operation, the O2 sensors are not used to trim air/fuel mixture and hence the name “open” loop. Closed Loop operation consists of an EEC controller that uses a target air/fuel ration contained in lookup tables (based on a Ford test engine) that uses the O2 sensors as feedback for making adjustments. If the output of the O2 (HEGO) sensors stay either below .33 volts or above .8 volts, then the engine is running too lean or too rich.
...
The EEC varies A/F ratios by varying the "pulse width" of the voltage applied to the injector solenoid. Pulse width is a term to describe how much average voltage is applied to an injector coil over a given time span - typically about 2.5 milliseconds for EFI cars. 12vdc is always applied to the injectors but when you average the applied voltage over a set time span, shorter pulses result in lower average voltage (leaner A/Fs) over that time period and vise-versa (richer A/Fs) for a given air flow quantity.
...
Anything external to the EEC, which that tries to modify the desired air/fuel ratio (based upon data from a Ford test engine – hence the name “base” Open Loop Fuel Table) in closed loop operation, will cause the computer’s Adaptive Control feature to try to compensate for the change by writing correction multipliers to KAM that correspond to the load level at which the out-of-tolerance value occurred. The Adaptive Control will also monitor how the engine is responding to the way you drive and make adjustments.
...
EEC Controls
The EEC sees only one crank position sensor signal, a short signal on the shutter wheel in the distributor shutter wheel. The Hall effect “pickup coil” as it is generally known has a magnetic field that is interrupted from the sensor by a wheel containing shutters that spin past the sensor. The signal output from the Hall effect sensor is called a Profile Ignition Pickup (PIP) signal. There is one shutter that is skinny and this is how the EEC knows the #1 piston top dead center position by its mechanical relationship through the timing chain and distributor gear. This is how the EEC knows where each cylinder is in the firing order due to monitoring the time rate between PIP signals (changing rpms) and the internal firing order data, which enables it to control sequentially the firing of the injectors.
...
The TFI module cleans up the PIP signal before sending it off to the EEC. The TFI also uses the Spark Output (SPOUT) signal, from the EEC, to determine when to fire each plug. The coil fires on the falling edge of the SPOUT signal. The TFI also provides an internal SPOUT signal (based on the PIP signal) for limp home mode operation if it senses the EEC has stopped sending the SPOUT. If the SPOUT plug is not inserted, spark timing remains at base timing during engine operation. The EEC controls the spark based upon lookup tables like the air/fuel mixture.
...
The computer interpolates (ratios) values for load and rpm between the table values so timing is adjusted for every cylinder firing. Once again the MAF signal and other sensors measure % load and a value of spark is chosen based upon engine rpm.
...
Adaptive Control
There is much confusion about how Adaptive Control works especially at WOT. Adaptive control, ... is always functional – at WOT and anything less than WOT. The difference is that in open loop and at less than WOT, this feature monitors O2 sensors and writes correction factors to KAM, which are applied to the table value Air/Fuel mixture injector pulse widths for future calculations. The rate at which Adaptive Control writes these correction factors to KAM is slow enough to filter out short duration upsets in the mixture. Short-term closed loop corrections are written to Long-Term Adaptive Strategy KAM if they repeat. At WOT the Adaptive Control still functions but it does not update (or write) correction factors to KAM for application to the base tables – it defaults to the already stored correction values, if any have been written, for the load and engine temperature experienced in the WOT load range.
...
Closed Loop
When the EEC reaches a point where it is satisfied with all monitored parameters, it will transition to closed loop operation. In this mode the EEC tries to control air/fuel mixture to the stoichiometric ratio of 14.7:1 and accomplishes this by adjusting injector pulse width with feedback from the O2 sensors to control to the 14.7:1 ratio.
...
EEC will not go into closed loop at a temperature less than 170°F.
...
If you place the HEGO O2 sensors farther away from the head than the stock location, you may have the sensor too far away to keep it hot enough to read correctly due to the cooled exhaust gases. This causes the EEC to enrich mixture and may cause plug fowling. Ceramic heat coating the headers will help maintain exhaust gas temperature. The EEC has a timing table used to time the sampling of the O2 sensors to coincide with the arrival of the latest cylinder exhaust pulse from each bank. Moving the HEGO sensor further away (or closer for that matter) may result in an ill-timed sample, which could also cause improper air/fuel mixtures to occur.
...
Another thing the '94 - '95 cars do with spark is retarding it during a shift. The automatic cars REALLY pull out the timing... Inside the ... EEC calibration is a thing called Tip-in Retard. Any time the throttle is moved from a more closed position to a more open position, it can pull out some timing.
...
The 94-95 automatic cars have a torque modulation strategy installed in them to vary spark during shifts. When the EEC thinks it's time to change gears, it can pull out massive amounts of timing so the shift is nice and smooth.
