Most fuel pressure gauges have a button on the side leading to a clear plastic hose. You push the button, gasoline vents down the hose, hopefully into a drain pan.
So if you're idling and have good fuel pressure...push and hold the button, let fuel dump into your drain pan. You've just tested the fuel pressure "under load". The fuel vented down the hose is about the same as the engine would use at heavy throttle. If the pump maintains reasonable pressure...you should be good.
What pushing the button does NOT simulate, is the loss of vacuum with heavy throttle...which would cause a vacuum-referenced fuel pressure regulator to increase fuel pressure. Not an issue on TBIs that don't have a vacuum connection on the regulator.
So if you're idling and have good fuel pressure...push and hold the button, let fuel dump into your drain pan. You've just tested the fuel pressure "under load". The fuel vented down the hose is about the same as the engine would use at heavy throttle. If the pump maintains reasonable pressure...you should be good.
What pushing the button does NOT simulate, is the loss of vacuum with heavy throttle...which would cause a vacuum-referenced fuel pressure regulator to increase fuel pressure. Not an issue on TBIs that don't have a vacuum connection on the regulator.