From this example, you'll quickly see why an adjustable pressure regulator might not be a good investment of your money. Ford uses a fuel pressure of roughly 39 PSI to rate it's fuel injectors. The fuel regulator operates in conjunction with manifold pressure to keep the delta pressure across the fuel injectors at roughly 39 PSI at all times. In the EEC calibration, there is a number that represents the size of the injectors installed in the engine. This number
represents how much fuel the injector will flow at 39 PSI. The EEC uses this number, along with airflow information to correctly calculate A/F ratio. Based on
the airflow number and its target A/F ratio, the EEC pulses the fuel injector to give just the right amount of fuel to reach its target A/F ratio at any given
Speed/Load point. Now if you were to increase the fuel pressure, the amount of fuel delivered for a given pulsewidth would go up since more fuel will be forced through the injector. As soon as the EEC goes into Closed Loop control, it will 'see' this increased fuel pressure. The reason for this is for any given pulsewidth, the A/F ratio as measured by the oxygen sensor will be richer than what the EEC wanted it to be since now there is more fuel delivered with the same pulsewidth. The EEC will calculate the difference from what it wanted and what it got and update the Adaptive table with a 'correction factor' and use this correction factor to reduce the injector pulsewidth the next time the injector fires. Eventually what happens is the EEC is able to 'dial out' the extra fuel that was added by increasing the fuel pressure. Now you can probably see why raising the fuel pressure is only a temporary 'fix' for a lean problem. Soon you will be right back where you started from. The EEC is continuously updating the Adaptive table anytime it is in Closed Loop.