Fuel pressure question - HELP!

[Mountain Main]

Lower residual pressure could be caused by leakage at the fuel pump check valve or the fuel pressure regulator. Or look for leaking injectors.

If there is no change in ER pressure, check the vacuum supply and hose to the pressure regulator. Fix if faulty. If the vacuume and hose are OK, then regulator is probably faulty.

On port injected engines, notice the difference between Key On, Engine Off(KOEO) pressure and the Engine Running pressures. With the engine OFF, Manifold Absolute Pressure (MAP) is higher than it would be with the engine running

-ER, idle fuel pressure is lower than Koeo because the fuel pressure regulator compensates for the lower MAP.

-ER, wide-open throttle fuel pressure is usually about the same as KOEO because MAP is about the same as it would be Engine OFF.

I think this will help you understand.

-ER idle fuel pressurewith the vacuum hose removed from the fuel pressure regulator is also the same as KOEO. Fuel-pressure gauge is operationg at barometric pressure, both cases.