1996 DeVille Fuel Pressure regulator
Just to help someone else out that may be having a similar problem.....
I have 1996 DeVille with the Northstar 4.6 engine and I have noticed that after I tuned up the car with new plugs and wires, replaced the fuel filter, and PCV valve the car ran smooth, but about the 39 to 41 mph speed the car would have a slight hesistation as it shifted. Not really that noticeable but enough for me to feel it. Also, after the engine was at operating temperature and if I stopped someplace and turned the car off, then get back in after 5 or 10 minutes, the car would sometimes "die" when I was not pressing on the gas pedal, like when you go down hill. The car always started back up and would not do it again. This symptom was inconsistent in that it did not do it all of the time, just occasionally.
This past weekend I decided to replace the fuel pressure regulator. This is an easy repair and the part cost me $50. On this car the fuel pressure regulator is located under the engine cover and on the back right side. All you have to do is to pull the retaining clip and the fuel pressure regulator pulls out. The one thing to be sure of is to get the small "O" ring out of the center of the where the regulator sits, otherwise you will never get the new one in. Take the new regulator and place back in the same spot, and work it down into its seated position. Attach the retaining clip and vac*** line and you are ready to go.
Once I did this, I have noticed a great improvement in throttle response, smoothness of the engine, and it has not died on me.
I hope this may help others.