My son has been trying to fix a problem on his Deville for over a year. He has replaced the fuel pressure regulator and fuel filter and had the distributor cap / plugs replaced. After driving it myself today, I thought I'd get on this board to see if I could get him some help. Local mechanics don't know what to do. The engine runs normally for about 20 minutes and then becomes choppy as you apply the accellerator. The engine stays on and idles fine at stop lights but power begins to diminish significantly over time, posing a safety issue for him and others on the road. The top speed decreases gradually until you're lucky to reach 5-10 mph. If you pull over and stop for 5 minutes, the car will start fine and run normally again until the cycle repeats. He's made this work because he just uses the car to get to and from work. However, college is coming and he'll need reliable transportation. If we can't fix this, we'll have to get a second car. He has a passion for the Deville and refuses to sell it.

Currently there are no codes. He says he's seen E.5.2 in the past. Its the 4.9L V8