Fuel Pressure Under a Load and at Idle?

[Seneca]

Hey guys, I have a Question about fuel Pressure Vs. Injector #numbers.
Okay Here's my Issue, I've got 39# injectors in my car, And i was checking Fuel pressures lastnight, At Idle I'm around 52psi Under a load i seen it go down to 27psi. Now, This is what i'm not sure of. With 39# Injectors, Shouldnt the pressure always be greater then 39lbs?

Thanks Seneca

[JMan]

Hey guys, I have a Question about fuel Pressure Vs. Injector #numbers.
Okay Here's my Issue, I've got 39# injectors in my car, And i was checking Fuel pressures lastnight, At Idle I'm around 52psi Under a load i seen it go down to 27psi. Now, This is what i'm not sure of. With 39# Injectors, Shouldnt the pressure always be greater then 39lbs?

Thanks Seneca

No! 39# (pound) injector rating is the amount it will flow (in fuel by weight) in a given time at a given pressure. In other words a 50lb. injector will flow twice what a 25lb injector will flow under the same conditions.

Your fuel rail pressure has to exceed the manifold pressure or the fuel won't spray. Under load/boost the differential between the fuel rail pressure and the manifold absolute pressure is 27psi. That's the fuel rail pressure to atmosphere less your boost pressure in psi. E.g. 9psi boost plus 27psi FRP = 36psi total to atmosphere. If you can raise the boost another 27psi, the car won't go WOT full boost:D.

Hope that answered more questions than it raised!

J

[Seneca]

I dont fully understand the Gasoline motors But that did help alot. thanks for the speedy reply. Seneca :)

[Zack]

What are you measuring fuel pressure with?

[Seneca]

Thru the OBD2 With the predator