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Old 10-17-2010, 05:02 PM   #14
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Join Date: May 2008
Location: Massachusetts
Posts: 925

let's try again.. still too long it's going in 2 parts

Here we go,

EEC IV Inner Workings

By tmoss

Last Revised: 12/17/2002

There are a lot of questions regarding the way the Mustang EEC IV works. I have spent significant amount of time searching for information regarding the EEC and I have come across readily available reliable sources of information. I don’t know that I can improve on the explanation of this information by pulling it into one document, but I am willing to try for the benefit of fellow Stangers. Many thanks to Authors such as Tom Cloud, Mike Wesley who have technical articles on the net, Charles Probst, who authored the "Official Ford Mustang 5.0 Technical Reference & Performance Handbook from which information was derived, and Mustang Forum members such as Rick Wagner, who used a EEC-Tunerâ and TransmarrowBird Eater (Dave) for sending me his TwEECerâ logs for graphing.


The EEC objectives include calculating required command values and outputting the required voltages to command, in real time, the spark timing, the EGR valve position, and for controlling the on/off duty cycle of the fuel injectors.


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. They are widely published on many web sites and so, will not be listed here.

Fuel Control

Determining how much fuel to deliver is accomplished in two ways, Speed Density (SD) control or Mass Air Flow (MAF) control. The mass airflow sensor measures the *MASS* of the air going into the engine. By measuring the *MASS* of the air, this helps to compensates for air density changes that occur with altitude and weather changes. 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 with the exception of the ‘94-’95 Mustangs which incorporate that function into the MAF. The SD system uses a Manifold Absolute Pressure sensor (MAP), which measures the absolute pressure (vacuum) in the intake manifold. When the ignition is first turned on, the EEC takes a quick reading of the MAP and stores that value as atmospheric barometric pressure for calculations during running. 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 for a 19lb fuel injector at 39 psi for a targeted air/fuel ratio that is stored in a multi-dimensional table for engine conditions as monitored from the engine sensors.

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. Here is a graph of the two output levels that signify out-of-tolerance values that cause correction factors to be calculated by the EEC and applied to the injector pulse width as well as being written to correction tables in KAM, which is called Adaptive Control. The Tweecer logs these as 3.2v & 4.9v values.

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 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. Your ET may improve slightly after several runs as the Adaptive Strategy shifts from street driving to drag racing. According to Mike Wesley, this control feature can only make adjustments in a range of 25% of desired values. EEC-Tuner user Rick Wagner has data logged his car and found that adaptive control only varies ±12.5% or 25% overall. Below are graphic representations of the Open Loop and Wide Open Throttle air/fuel ratio "base" table for an A9L Mustang computer and a 95 Mustang computer.

Notice that there are variances between the table values for different year cars. These tables also vary for differences in transmissions, etc. % load in the graph table is calculated by the MAF based on airflow and other sensor inputs. In the case of SD (not illustrated here), the load is based on Ford’s volumetric efficiency (VE) values for the 302, which are contained in the EEC tables.

EEC Controls

Functions controlled by the EEC are: air/fuel ratio in closed loop, EGR position, (gasoline) canister purge, thermactor system, adaptive control system, fuel injectors, transient fuel, spark, VE tables, rev limits, and much more.

Closed loop operation can sometimes be modified without problems and within EPA guidelines. This has allowed some manufacturers to market cars and parts that are emissions legal (e.g. Kenne Bell – for which Mike Wesley has done work, and Saleen). Approximately 900 items in a 93 Mustang can be changed or logged. For example, during a shift, the EEC might look at spark, load, TPS, fuel, and transient fuel. By logging this data, you can tell just where in the table the EEC is looking and tune those cells only rather than tuning the whole curve or somewhere where the EEC isn’t even looking at table values. Below is a graph of data collected by Rick Wagner, which illustrates the conditions under which his EEC made the transition to closed loop. One thing that stands out here is that temperature is only one of the parameters that the EEC looks at for closed loop. This A3M computer (same base tables as A9L) went into closed loop with ECT temps down to 140 degrees.

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 also 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. Below is a figure of a good PIP signal, which is routed through the Thick Film Ignition (TFI) to the EEC for processing and timing control, which the EEC then sends the signal to the TFI module to actually fire the coil. The EEC senses the coil ground for feedback that the coil has actually fired as commanded by the TFI.

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. Below are figures of the A9L spark table with conditions under which it is modified and a ‘95 spark table. 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. Notice that at 190°F the EEC pulls 2 degrees of timing. Also notice that at Wide Open Throttle (WOT) that spark is determined by engine temperature and rpm only. The spark curve is not really aggressive when compared to distributor curves of pre-computer controlled cars. This is one table value that can be changed for better performance. Performance mechanical advance distributors have full advance by about 2,500 rpm. Notice in this table that the EEC timing doesn’t all come in until 5,000 rpm at WOT. Note: This table may DIFFER for different model/year of EEC controllers.

The WOT Air/Fuel table is used during wide-open throttle only. Below is the Open Loop/WOT fuel/air table and it’s modifiers for WOT. Notice fuel enrichment is increased through 3,800 rpm where it is reduced with increasing rpm.
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