Fuel pressure regulator : more information wanted

I am attempting to gather as much information as possible about the fuel pressure regulator, how it interacts with various systems, what operating symptoms might be present due to its abnormal interaction with these systems when it fails, and how variable it can be in the way it fails.

For example, apparently the failure or partial failure of this part can result in hard starting. I have been told that this is because the ruptured diaghram can vacuum gas into the intake, and then into the cylinders. I do not entirely understand this, as I would think the intake of gas would stop as soon as the engine did.

If anyone can provide me with more information about the FPR, it would be greatly appreciated!

bump......

The fuel pressure regulator adjusts pressure at it's output by restricting the fuel that passes through it. These regulators are referenced to engine vacuum so that they can maintain fuel pressure regardless of engine fuel consumption. Our cars actualy increase fuel pressure for each PSI of additional pressure.

There is a valve in the regulator, made up usually of some sort of rubber.

The primary failure mode of the regulator is for the diaphram to rupture. When this happens, high pressure fuel is forced through the regulator and no longer "regulated". It also will cause fuel to be sucked into the vacuum line used for referencing the the regulator due to the way a vacuum works.

Since the vacuum is created via a venturi in the intake piping (at or after the throttle plates), this causes more than the metered amount of fuel to enter the intake stream of the engine. Thus a very rich condition.

Since when you shut off the engine, pressure is not immediately released in the fuel system, this remaining pressure pushes fuel into the intake system. this fuel and it's vapors get into the intake manifold and drip fuel into the cylinders. Wetting the spark plugs and washing the cylinder walls. Thus a hard start (the fuel pump has to build pressure, the spark plugs are wet, and the cylinder walls are no longer slippery so the engine cranks slow)

I think that covers it.

Excellent response Mike and precisely the information I was looking for. Thanks!