The fuel pressure regulator is a vacuum
operated diaphragm relief valve with fuel pump
pressure on one side and regulator spring
pressure and intake manifold vacuum on the
other side. The fuel pressure regulator
maintains a constant pressure differential across
the injectors at all times. The pressure regulator
compensates for engine load by increasing fuel
pressure as the engine vacuum drops.

These valves can rupture inside and allow fuel
to enter the vacuum line. This is a common
cause for hard starting, rough idle for a few
minutes after starting, or stall after starting.
Fuel Pressure Regulator (FPR) Description

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