|The point of the FPR is to equalise the pressure drop across the two sides of the injector. With the engine off you've got (typically) 2.5 bar of pressure ready to push the fuel through, but with the engine you've got a variable amount of vacuum or pressure pulling or pushing against the fuel flow and altering that 2.5 bar. With that variable pressure a given injector pulse width will mean different amounts of fuel got injected. You can't simply compensate for this by changing your injector duration as the ECU can't possibly predict what the pressure on the other side of the injector is as there's too many variables involved. You could do it with a pressure sensor that the ECU could read, but then you're simply trading a simple mechanical device for a complex electrical device and additional ECU complexity. Having the FPR there means that you ECU can always rely on having the same amount of pressure across the injector to work with.
Also, if you didn't compensate for the pressure differential with an FPR you'd have to run your injectors at an additional 1 bar + boost pressure to be able to feed the same amount of fuel to the engine as you could with an FPR, and that introduces another bunch of things you'd have to account for (such as low speed controllability due to injector pulse widths having to be a lot smaller).
From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Michael Parker
Sent: Saturday, 22 September 2012 12:05 a.m.
To: Supra Club of NZ Mailing List
Subject: RE:[sconz] 1G-GTE fuel pressure with 440's?
What is the point to the FPR? I have never understood it, from my understanding with no power to the solenoid there is no vacuum at the FPR the fuel rail see full pressure, but if the ecu opens the solenoid the FPR gets vacuum on its diaphragm and opens letting more fuel flow out reducing the fuel rail pressure? yes no?
Why not not just inject less fuel using the injectors rather than messing round with vaccum lines and a fuel pressure regulator that changes depending on how much vacuum there is?
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