Does fuel pressure raise when idle is raised.

[Justin]

When doing a fuel pressure test or checking the proformace of fuel pump. With the gauge hooked up and idle is raised does fuel psi raise? I think it does if I remember right. Also if you raise the idle and pressure drops your pumps weak. Am I right

Topic

[Bill]

When you open the throttle the manifold vacuum drops and the fuel pressure regulator should allow the pressure to rise.

If the pressure drops by any amount you can suspect a weak fuel pump, plugged fuel filter or defective fuel pressure regulator.

Newer vehicles are a whole new ball game if the fuel pump is computer controlled.

[Lorrin Barth]

On vehicles with fuel pressure regulators, the idea is to maintain the same difference between manifold pressure and fuel pressure at all times the engine is running. However, as the throttle is opened or closed, manifold vacuum (or in a turbo setup, sometimes manifold pressure) is constantly varying. So, fuel pressure changes to keep in step with changes in manifold vacuum or pressure. They do this to simplify injecting the proper amount of fuel.

[Author]

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