The fuel pressure up system (FPU) is designed to reduce the possibility of vapor formation in the fuel rail after hot soak and is used on many TCCS engines. It utilizes an ECU controlled Vacuum Switching Valve (VSV) to open an atmospheric bleed into the manifold reference line to the fuel pressure regulator.
This solenoid is energized during hot engine cranking and for up to two minutes after the engine starts. The ECU grounds the FPU
VSV based on input received from STA and THW signals. Energizing the solenoid bleeds atmospheric pressure into the fuel pressure regulator vacuum chamber increasing fuel rail pressure to its maximum level.
On some engines, the ECU also monitors engine load and rpm signals (Vs, PIM and Ne) and energizes the VSV under heavy load and high rpm operation to ensure maximum fuel rail pressure.
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