DeanHensler

The plugs and wires are AC Delco and I haven't changed the O2 sensor(s).

I've got a 2003 2500HD with the 8.1L. I am the original owner and have taken exceptional care of this truck. Lately, I have been getting some extremely random misfire conditions. I changed the plugs and wires at 100k (18 months ago), the truck now has 123k on it. Within the past month it has done this three times. The first time it was just a cold morning and I started the truck and immediately it had a rough idle and I could tell while driving it, it was down on power. This lasted about 5 miles and once the truck got warm it went away. The second time it happened I had already been driving the truck for about 30 miles, including towing a camper and I stopped at a car wash after dropping the camper. Immediately after the car wash (this was a handheld power washer) it started misfiring again. I hooked up my ODBII scanner and it pulled a P0300 code. Since then I've made a 1200 mile round trip drive into the Rocky Mountains and had zero issues. Today the same thing happened. I was towing a trailer about 20 miles, dropped the trailer off and went through a drive through car wash. After the car wash it immediately started the misfire problem the rest of the drive home. After sitting for an hour I went out and started the truck and it ran fine. I'm uploading some video's and will post them as replies when youtube finishes. Any thoughts what might be causing this? I opened the air filter box and while the air filter seems dry, there was a little bit of water in the bottom of the air filter box. The top of the engine was completely dry.

Thanks GM! That sounds super easy to access!

Where exactly is the oil pressure sensor located on a 2003 GMC 2500HD with an 8.1L engine? Pictures or youtube videos would be greatly appreciated!

Has anyone changed the fuel pump in their 2003ish 8.1L? Mine is starting to make a noise and I want to replace it as preventative. Curious what part number is best as I don't want to do this job twice!