For our custom tune on the...
For our custom tune on the stock Cobra, we modified only the scalars shown here. The changes made in the Powertrain Limiting and Transmission Configuration sections created a 3,500-rpm "two-step" rev limiter we could use at the dragstrip. Neat, huh?
With access to over 70 tables, almost 100 functions, and over 260 scalars to modify in our Cobra's "AMZ1" (EEC code) processor, the complexity of the newer Ford EECs is again reinforced. In the end, we ended up changing eight tables, six functions, and 36 scalars. In the interest of keeping this already long series from getting excessively long (and to keep from giving away any proprietary info), we can't go into each and every last modification, but we will cover the main tuning mods-things your average DIYer would go after.
Stock Cobra
First things first: Before we started modifying the Cobra, we tuned it in stock form to see how much power was left on the table by Ford. Keep in mind, we're not tuning on the ragged edge here (Cobra engines aren't cheap), so our newfound power comes with a tune that's still safe for pump gas.
For EEC V systems, the ECU...
For EEC V systems, the ECU can still make use of a J3 device, but internal memory became flash reprogrammable. Through the magic of OBD-II (and we all thought it would be a bad thing when it came out in 1996), you can now use a Flash Tuner tool such as the DiabloSport Predator or SCT XCalibrator to simply flash a new tune into your EEC through the OBD-II service port, without ever having to "find" your actual ECU. For '05-and-newer Ford ECUs, the J3 port is now gone, so flash tuning is your only option. An advantage of flash tuners over chips is the ability to integrate OBD-II diagnostic features into the hand-held unit, such as service code retrieval (and clearing), and data logging of the EEC sensors and actuators.
On the Superflow chassis dyno rollers at Motion Performance in Winnipeg, Canada, we baselined the Cobra at 382 rwhp, at just over 6,000 rpm, with a peak rear-wheel torque figure of 365 lb-ft at 3,800 rpm. Throughout the run, the A/F ratio was quite rich, then it got really rich at the end, most likely due to the combination of a learned fueling correction (from an unrelated low load/rpm point), and the stock tune adding even more fuel to cool the catalysts at high rpm.
Now it was time to look for improvements in the tune. Our gameplan was to get the A/F ratio where it would make more power, but without being risky (read: lean). Similarly, we'd add a bit more spark advance, knowing our 94-octane pump gas gives us a bit more protection from detonation than the 91 octane specified in the owner's manual. We'd also be data logging the ECU, so we could monitor all important parameters to ensure the ECU was doing what we wanted it to do, while also ensuring we weren't getting to the limit of the stock MAF sensor or fuel system.
Modified Scalars
For our unmodified Cobra custom tune, we first disabled the adaptive strategy by setting "adaptive fuel enable" to 0, so we weren't competing with the ECU to straighten out the tune. We then disabled the rear O2 sensors, since we'd be putting the dyno wideband O2 sensors in those same bungs. While we were in a disabling mood, we also disabled traction control by setting the "axle ratio fractional" value to 0, disabled the boost bypass, disabled torque modulation, and finally we disabled the catalyst temperature models, which dump a bunch of power-robbing fuel into the mix when the ECU thinks the cats are getting too hot (which showed up in the baseline dyno run when the A/F ratio fell off a cliff towards the end of the run).
Other important changes to the scalars included lowering the fan control temperatures to keep the engine a bit cooler (for more power), reducing the OL delay transition, setting the maximum acceptable MAF sensor voltage to 4.99 (so we get the full usable range of the MAF sensor), and bumping up the WOT air charge numbers, which the ECU uses to estimate WOT airflow.