[updated:LAST EDITED ON 04-Dec-02 AT 05:34 PM (EST)]The truck was running great and then just out of the blue it is running rich. A few people have suggested that an injector could be staying open. What is the procedure for checking this?

 

Probably the only way to identify it would be to put a pressure gauge on the fuel rail - there's a schrader valve for it near the back. I'd expect to see a momentary & irregular drop in pressure, but very slight.

 

With a pressure gage on the fuel rail, if there is a leaky injector, you should see the fuel system pressure go to 0 psi when you shut off the engine, or you can just turn the ignition switch to ON (not START - when the key is in ON, the fuel pump runs for a few seconds then stops). This assumes that the fuel pump check valve is working, there are no other fuel system leaks (internal or external) and that the cause for the injector staying open is mechanical and not electrical such as a short in the wires.