I just picked up a 1998 GMC SL2500. The issue i am having is In order to start it You have to spray it with either, then it fires up and WILL stay running until I put in drive/reverse.
I opened the "Port cap'' on the fuel rail and nothing spits out, I thought it was the fuel pump in the tank but I can hear it trying prime/pump, I also bought a fuel pump relay-- no results.
No sure what my next move is----I truly appreciate any and all help--Thanks Bones

 

The port cap you opened has a schrader like valve in it, and unless you depress the center pin, nothing will come out. It is the test port where one screws on a fuel pressure gauge to see what the fuel injection system pressure is.

What you really need to do is get a fuel injection pressure gauge (you can get a loaner from AutoZone, O'Reilly, or Advance Auto Parts) and see what the fuel pressure is when you turn the ignition key to ON and the engine is OFF. Then also check the pressure while the engine is running. While you are at it, test the fuel pressure regulator for proper operation. If the engine running fuel pressure is below the specified pressure, then you likely have a faulty fuel pump. If you are unsure of the vehicle's history, you might want to install a new fuel filter and see if that helps your starting issue. Also, visually inspect the fuel lines to make sure they are not kinked.