I'd leave the FMU on even with the injectors. If the manifold had 6psi of boost, and the regulator was set for 40 psi and has no connection to the manifold, the pressure on the injector is 34#'s. You need to overcome the pressure working against the injector inside the intake, that's where the FMU comes in handy. Confused yet?
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92 GT, 4:10 gears, centerforce clutch, 6# powerdyne blower, bbk h-pipe, flowmasters