Checking your fuel pressure is a piece of cake, here's how to do it.
On the passenger side, follow your fuel rail until you come to a valve, it has a black cap similar to a valve stem cap on a tire ,yours may have been removed, and not be there, the valve itself also looks similar to a tire valve, this is called "The Schraeder Valve"., you must remove this valve first. This is where you hook up your fuel pressure gauge.
Now!, you must relieve the pressure (38-42psi) before you can screw on the gauge, I recommend letting the car sit over night, and doing the job in the morning when you are fresh, and the car is cold and will have relieved a little pressure, wrap a few shop rags around the valve, then push the little pin in (easy does it now, safety first!) to let the fuel squirt out into the rag, if any. Then remove the valve ( a tool usually comes with the gauge). Screw on your fuel pressure gauge using teflon paste NOT tape and your ready to check your pressure.
Once again I really recommend doing this when the car is ICE COLD, I have seen a few 5.0's and garage burn to the ground because the owner was so hot (pun intended) to install his new gauge and regulator after driving the car home, by gas hitting the hot headers, and Voila! broiled mustang, not good. Good luck and try me again if you need more info.
