Wow! Wild effect by FPR on fuel pressure. With 100psi FP tester in place and return hose rerouted to container, started engine. Idled a lttle weak with FP around 38-40 and unsteady. Pinched return hose lightly by hand and controlled pressure fleetingly at "steady" 43.

Suddenly engine stalled and pressure jumped past 100psi to pin, maybe 120+ psi. Tester has relief valve so I dropped press quickly and it stopped at 10. Thought maybe gauge damaged but second tap on relief dropped reading to "0".

Engine is m30 with Walbro 255lph pump replacing OEM as we are thinking about turbo.

Obviously unreliable FPR, but how bad was the 120psi on the fuel system? Anything damaged? Bentley calls for FP tester range to at least 75. 120 from the high flow Walbro seems credible.