Recommended Procedure (With Scan Tool)
WARNING: This page is about a different car, the 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, 2003 Ford Excursion, and 2003 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
Monitor scan tool PID MGP and RPM. After the engine is up to operating temperature, find an open section of road and select the best gear to achieve a 3300 RPM acceleration. With the accelerator at WOT, note the highest boost reading while accelerating through the 2500-3300 RPM range. Boost will level out after 3300 RPM. This is best accomplished either climbing a hill or with the vehicle fully loaded. MGP should reach 22 psi minimum.