[Mike51Merc]

You probably have a liquid filled pressure gauge. They often give false readings when warm/hot because the liquid inside expands and counteracts the fuel pressure sending the needle to zero. If your inlet needle valves were stuck closed, your inline pressure would be maxed, not zero.

You may be able to fix the gauge if it has a rubber plug on it. You can burp the pressure out, or empty some of the gauge fluid.

At least that will put you partly on the road to diagnosis.