can anyone tell me the correct way to find out the fuel presure on an eb falcon v8 ? and what should the presure be at and what is to high and what is to low? my fuel presure is 80 psi and my cars exhaust tips are black and also runing rough and stalling.

How do you know the current fuel pressure is 80psi?

There is a schrader valve in the drivers side fuel rail towards the front. A schrader valve is same as the as you use to inflate a bicycle tyre...

You can get a guage to that hooks up to the schrader valve, or you can remove the schrader valve from the rail and fit an autometre guage or similer with a 1/8th NPT fitting.

Fuel pressure should be 38psi at idle with the vacuum line removed from the regulator (firewall end of passengar side fuel rail). Or closer to 30-32psi at idle with the vacuum line connected.

Yeah I highly doubt your fuel pressure will be at 80psi unless you have a high performance fuel pump, the stock pump just wont be able to maintain that sort of pressure IMO. Also I doubt the car would even start and idle with that sort of pressure either.

As xr8ute said, normally pressure is tested using the schrader valve on the fuel rail, or you can also check it with a t-piece in the rubber part of the fuel supply fuel line on the passenger shock tower depending on what fuel guage you have.