KN4 - Check Vacuum Signal Between FPRC Solenoid and Manifold

- Key "OFF".

- Tee in a standard vacuum gauge at the hose between the manifold vacuum source and the Fuel Pressure Regulator Control (FPRC) solenoid input vacuum port.

- Start and idle engine while observing the vacuum gauge needle.

- Was a vacuum signal present?

Yes -- Remove vacuum gauge. Go to KN5. KN5 - Check Vacuum Between FPRC Solenoid and FPR

No -- Address base engine vacuum source concern.