Originally Posted by Rallyesport
There is no normal way to increase the fueling on an rst. The system is very simple. There is no need for increasing the fueling by using the fuel mod which alters the base pressure by turning the screw on the back of the electro magnetic fuel pressure regulator. The KE-Jet unit will fuel more on 12 PSI, because the paddle will go deeper beacuse of the greater air flow. The only thing you will have to do if you want to boost more than 12 psi is to change the chip, then you can go to 14.5 psi without out doing anything else. Please don't argue this, it will only show you take your car to the garage to change your spark plugs or light bulbs.
Your RST's metering unit must have had an uprated spring fitted and the KE fuel ecu current trimming caps altered as the std air flap bottoms out around 7psi
Also, has the car IN QUESTION been modified by Ford at service time back when the RST was pretty new? The mod that was specified by FORD themselves due to the KE Jet system running slightly lean?
Ever wondered why some run rich and some lean folks? Soem will take more boost safely and others melt? Now you know... Ford technitions all seemed to have a different opinion of how to perform the TSB's simple instruction:
"Rotate the screw no more than 15degrees clockwise"