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Message: <blockquote data-quote="MrNismo" data-source="post: 118466" data-attributes="member: 13">Hi zephuros,The good thing about an in-dash fuel pressure meter is, you can monitor the fuel pressure changes during full boost, which a regulator-mounted type can't. When you rev the engine during idle, there is not much load so the injectors won't be firing that much, and the fuel pressure won't rise up that much either. Aftermarket rising rate FPR are supposed to regulates fuel pressure according to boost as I say. So lets say with the vacuum hose unplugged, fuel pressure is 47psi (around 3.2bar), so during a boost of 0.7bar (assume that is your full boost), your fuel pressure are supposed to be around 3.9bar (3.2+0.7bar). Fuel regulator holds the pressure by restricting the flow back to the fuel tank. So if your fuel pump is not pumping enough volume, and your injector is firing up, there is not much restiction in the high pressure line, hence, fuel pressure drops (again you need a in dash fuel pressure meter to confirm this, no unless provided that you cut a hole in the bonnet and stick the fuel pressure meter out aussie style). Well that doesn't necessary mean that your fuel pump is giving up. A weak regulator might give the similar situation. Now you get why I meant by 47psi during full boost is bad. Lean mixture promotes knocking heheheh... my RB20DET used to knock a lot coz I'm using a tiny winy fuel pump... someone in this forum even blew his RB20DET engine caused by weak fuel pump...The Apexi pen timer doesn't give accurate result. It calculates the A/F by using the stock narrowband o2 sensor voltage. Any slight difference in the electrical system voltage can affect the readings, for eg. on/off aircond, on/off headlights and so on...</blockquote>