On rail FPR

[b*saint]

Just to clarify, the higher the vacuum the further the FPR opens to allow more fuel correct?

[whodwho]

Its the opposite. When you have high vacuum(idle/decel) the fuel pressure is lower, lower vacuum(WOT/boost) the fuel pressure is higher.

[jlevie]

Correct. high vacuum reduces rail fuel pressure. The only time one has high vacuum in the intake is when the throttle is closed and thus the need for fuel is reduced.

[b*saint]

When I say high vacuum I mean say 20 inches. When I say low vacuum I mean 5 inches. Maybe my logic is backwards. In our industry a high vacuum is 2 torr. A low vacuum is 150 torr (closer to atmosphere)

[whodwho]

And I believe we are saying the same, more vacuum opens the FPR further and decreases fuel pressure in the rail

~20"Hg / idle opens the FPR and decreases fuel pressure = less fuel
0"Hg/atmosphere / WOT closes FPR and allows more fuel pressue = more fuel
Positive pressure / boost allows even more fuel by closing the FPR further increasing the rail pressure

[b*saint]

I thought the vacuum increases as the throttle opens. Learn something new everyday. Im such a n00b.