Help!!! 1994 Ford F350

I have a FORD 1994 F350 and the check engine light comes on and begins to run rich and gets poor MPG. When the light goes off it appears to run ok again, but then the light comes on again. I had the codes read but it did not show any. Pls help in any way possible. Thanks :)

Just a guess would be oxygen sensor but usually that will set a code so I'm stumped too. Good Luck

1997 F150 215,000 Miles

Pull the vacuum hose on the fuel pressure regulator and if leaking replace it. You can use a pressure tester and check fuel pressure.
http://www.autopart.com/tools/toolsmain/tool/T_3440.htm
This is a picture of what it looks like you can check if your parts store carries them.
Look on the fuel rail for the injectors.