Why does Toyota try to keep the fuel pressure XX Kpa above intake pressure.... I am curious as we are considering replacing the Fuel Pressure Regulator but the OEM FPR has a vacuum line going to the intake... Anyone have any insight?


thanks.

When you have maximum vacuum, your throttle is closed and your at idle. So your fuel pressure should be low. As you increase your throttle opening, the vacuum drops therefore you need to increase fuel pressure for your injectors. It gets to the point where you only have 15 kpa of vacuum your throttle should be wide open and your fuel pressure regulator should be fully off and your at maxium fuel pressure allowed by your fuel pump.

This post has been edited by Hanyo: Nov 23, 2009 - 6:02 PM

the fuel pressure being pumped through the fuel line isn't constant. like most pumps in general, there's a cyclic pattern in the fuel pressure curve. all the regulator does is allow fuel to flow through it while a built-in diaphragm absorbs the sudden changes in fuel pressure for a more steady flow.

i'm not sure how many types of fpr's there are but most OEM ones have diaphragms that operate using the vacuum from the intake manifold to regulate pressure.. then there are aftermarket ones that have diaphragms which can be adjusted using the built-in spring instead of the intake vacuum.

so as fuel pressure increases, you'll need an fpr that can perform beyond oem thus the need of an aftermarket fpr.

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That makes sense functionally... but what is the benefit? what is the motivation for changing the fuel pressure?