Changed a compressor regulator and dryer on a low mileage 1990 9300 350 Cummings. Problem won't build past 55 psi, adjusted regulator in a little better still wont climb past 55 psi????
Well figured it out, mounting of the new dryer obscured the correct port for the return line to the governor, hence it pays to have friends looking over your shoulder and the correct technical info.....MY BAD!