FP Stupid question

[Jsup]

Ok, I know this is stupid but I'm having a brain freeze right about now.

is FP checked with the Vacuum ON at idle, or OFF?

Thanks

 

[mrvette]

FP= Fuel Pressure??? typically checked with engine off, pump running, AFAIK.....but at idle, expect a bunch less....

as the pressure reg is connected to mani vacuum and as such reduces the spring pressure, and therefore opens the bypass valve on the fuel side of the diaphram....and reduces the available pressure....

so with the engine running, that mani vac can be all over the joint, depending on cam, idle speed, even load...not that it matters much on the load with a computer engine because it sets the IAMotor to such a air intake to keep engine at programed RPM.....

:thumbs:

 

[big_G]

Ok, I know this is stupid but I'm having a brain freeze right about now.

is FP checked with the Vacuum ON at idle, or OFF?

Thanks

ON. This will be your base line fuel pressure, usually 43 psi. Under full load (no vacuum) the pressure should rise.

 

[mrvette]

Ok, I know this is stupid but I'm having a brain freeze right about now.

is FP checked with the Vacuum ON at idle, or OFF?

Thanks

ON. This will be your base line fuel pressure, usually 43 psi. Under full load (no vacuum) the pressure should rise.

Something rong with my basic understanding??? I thought it almost had to be with engine off, pump on....as pulling the vac line will easily stall the engine in most applications....too much fuel...flooded....NO??

What I don't understand??

:clobbered:

 

[big_G]

Never seen a running engine stall or even run rough by pulling the f/p regulator vacuum port. The fuel pressure only rises about 8 psi.

 

[Twin_Turbo]

Best checked with a hand vac pump or some other gizmo where you can pull a controlled (and readable from a gauge) vacuum to see the pressure drop.