I have a question about vacuum....anyone know what the vacuum should be on a 5.4 2002? I'm assuming there should be one pressure at idle and the RPM's go up, the vacuum reduces or does it increase? Anyone know what those pressures should be typically? Do the PCV hoses always have a negative pressure? Or does it ever go to 0 or positive?

 

18-22 in/hg at idle, with the needle holding steady, is about normal for a healthy engine at idle. Snap the throttle wide open and the gauge should go zero then slowly rise back to 18-22 in/hg.

As engine speed increases, vacuum decreases. Remember, the engine is an air pump; turn the pump faster, more pressure is generated.