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When you say it may need the schrader valve removed, what do you mean? On the gauge itself or are you talking on the fuel rail?
I've checked the fittings. The gauge I have is set up with the large threaded end on the hose, and then an adapter to go on the smaller (schrader) fitting. I have done several combinations of things, including screwing on just the small fitting onto the valve on the rail, and depressing the valve. A little trickle comes out, and I have checked the adapter in the gauge and it does seem to fit correctly and actuate the little pin in there.
It's still confusing to me that when I depress the pin in the valve on the fuel rail, I'm not getting a spray of fuel coming out of it with the system pressurized.