Injectors do have a small...
Injectors do have a small amount of inertia in the valving. As a result, when current is put to the injector, it takes a slight amount of time for the injector to fully open. As battery voltage drops, the injector coils are less energized, thus the injector opens even slower. To compensate for this behavior, the injector PW is compensated for battery voltage, such that more PW is added when the battery voltage drops.
MAF Sensor
For MAF-based EEC systems, the MAF sensor accuracy is critical. To calculate the correct fuel flow during Open Loop mode, the ECU relies heavily on the MAF sensor. So if the MAF sensor accuracy is off, the WOT A/F ratio will be off, too. Unfortunately, many of the larger, better-flowing aftermarket MAF sensors are not as accurate as they should be. But even with an accurate MAF sensor (like a factory unit), as soon as you change the airflow path either before or after the MAF (like adding a cold-air intake system, for example), or change the orientation of the MAF (i.e., rotating or "clocking" the sensor), the MAF sensor accuracy usually goes south. But all is not lost, since we can reprogram the ECU for the actual mass airflow versus voltage output for the particular sensor and plumbing/clocking used.
The Ford EEC uses a function for the mass flow versus output voltage of the MAF sensor. Anytime a new MAF sensor is installed, the "MAF transfer function" needs to be updated. For many MAF sensors, baseline transfer functions are available (sometimes included with the meter), but most often further tweaking is necessary to get it right. This is where EEC datalogging is critical to get a proper, custom tune.
If you're using a MAF sensor calibrated for larger injectors (usually a necessity, as mentioned earlier), enter the actual airflow versus voltage, and actual injector slopes, so the ECU can calculate load correctly. But instead of entering the actual MAF transfer and injector slopes, an alternate tactic is also used by some tuners to correct the calculated load: scale the engine cid.
Since the calibrated MAF/injector combination "should" calculate the fuel PW correctly without reprogramming the ECU (as explained earlier), reducing the engine cid in the programming will still allow the ECU to calculate load correctly. Load is calculated by comparing the actual airflow to the theoretical maximum airflow (which would depend on the engine displacement). The recalibrated MAF sensor is telling the ECU there is less air flowing into the engine, so if you also tell the ECU the displacement is proportionately less, the calculated load should be correct.
Scaling the cid is certainly quicker and easier than reprogramming the MAF transfer and injector slopes, so it's a shortcut for many tuners. But it's also viewed as a lazy-man's approach to tuning, since you're still trying to "fool" the ECU.
Here we show a stabilized...
Here we show a stabilized OL fuel table from a T4M0 calibration ('94-'95 Mustang 5.0 five-speed). Note how the programmed A/F ratio gets richer at high loads.
For some vehicles, however, the ECU "fooling" approach for the MAF sensor is unfortunately mandatory. Many Ford EEC systems from 1999 to 2004 had a 64-lb/min airflow limit for the MAF transfer function built into the programming. Using larger MAFs, for larger injectors, would easily exceed this 64-lb/min airflow at 5 volts. Because we can't reprogram the MAF transfer function for airflows beyond 64 lb/min at 5 volts, the solution to the problem is to use a device to reduce the MAF voltage output (like a MAF Extender or DiabloSport MAFia), then similarly reduce the injector slopes and cid scalars in the programming, so the ECU's PW and load calcula-tions are correct. For example, if we used a MAFia set to reduce the MAF output voltage by 50 percent, we would reduce injector slopes and cid by 50 percent as well. This technique allows you to measure up to twice the 64-lb/min airflow limit, without "pegging" the MAF sensor.
Fuel-Control Basics
Before we get into the fuel-control programming, we need to introduce another parameter, "Lambda." Lambda is the ratio of the actual A/F ratio divided by the stoichiometric A/F ratio (which for gasoline is about 14.64:1). A Lambda value greater than one means the A/F ratio is greater than 14.64, and vice versa. Also, as Lambda values increase, A/F ratios are leaner, and vice versa. Depending on the tuning software used, the fuel functions and tables can either have A/F ratio values or Lambda values, so it's important to understand how Lambda works.
Fuel-control strategy varies depending on operating modes and the EEC strategy. In general, fuel control can be separated into the following modes: startup, open loop, closed loop and WOT (WOT is normally OL).
In the early EEC IV days,...
In the early EEC IV days, WOT spark timing was controlled by the WOT spark advance versus rpm function, shown here. Later EEC IV and all EEC V dropped this function, so WOT spark was determined from tables.
Startup mode intentionally richens the A/F mixture to compensate for cold engine-fuel volatility problems. Enrichment depends on coolant temperature, and time after starting the engine, so the startup fuel enrichment is a table in the Ford EEC. Values in the startup table subtract from the current OL A/F (or Lambda) values. For example, a '95 5.0 Mustang shows a value of 2.63 in the startup fuel table for an ECT of 60E F and 10 seconds after startup. This value is then subtracted from the OL A/F value of 13.27, to get a final A/F target of 10.64.
For modified engines with larger injectors, the startup fuel table is often too aggressive at warmer coolant temps, which causes hot starting prob-lems. The solution is to reduce the startup fuel table values at the higher coolant temperatures.
For OL fuel, there can either be a stabilized OL fuel table and base OL fuel table, or just the latter depending on the calibration (earlier EECs had only the base fuel table for OL). The difference between the two is primarily ECT. At colder ECT, the base fuel table is used, but once the engine warms up and the temperatures stabilize, the stabilized OL fuel table is used. Depending on the tuning software used, there is a scalar value that determines at what ECT value the EEC should change fuel tables.