To check fuel pressure, you're right. There is no Schrader. On this vehicle, it is necessary to remove the fuel supply line, add a T between it and the fuel rail, and then the last leg of the T is where the gauge attaches.
If the spark plugs are wet, it could be an injector or injectors. However, I wouldn't think all would fail at the same time. Are all spark plugs getting wet? If it is only one or two, an injector may be leaking causing the issue. However, to determine if that is the issue, we would either need to check fuel pressure drop off with a gauge or remove the injectors and test them.
Here is a link showing how to test an injector:
If you look at the attached pic, I added a pressure test kit. I circled what you need and highlighted where the Schrader is located. Basically, it is spliced into the fuel supply.
Let me know if that helps or if you have other questions.
See pic below.
Image (Click to make bigger)
Tuesday, April 19th, 2022 AT 4:53 PM