I have a 2004 MC with the 3400. So yesterday on the way to work I noticed a rough idle while sitting in the drivethru. I thought well maybe it's just a dirty butterfly valve. I'll clean it when I get home. I also noticed the cruise control was struggling a little bit to maintain a consistent speed. I did not give it much thought. On the way home the check engine message popped up.I also noticed my gas mileage was terrible. After arriving home I pulled the code P0171. Ok, I thought, here we go down the rabbit hole. I opened the hood prepared to check the fuel pressure and the first thing I saw was the little vacuum port next to the F.P. regulator was exposed. The rubber remnants surrounded the nipple. I thought to myself, it cannot be this easy. I removed the rubber remnant and dug thru my stash and found a proper size nipple. I cleared the codes and drove it down the road. Problem fixed. Maybe I need to go buy some lottery tickets? See attached pics.

 

Nice when a problem ends up that easy to find.