I picked up a 1999 F-550 7.3 auto at auction a couple weeks ago. It was running slightly rough when I got it which i just figured was a stopped up fuel filter or old fuel as it had been sitting for a while. There is no smoke or unusual blow by. Changed the filter and drained/replaced the fuel and drove it about 25 miles with no change. After doing some research I decided that the UVCH was the place to start. I pulled the valve covers and put my multimeter to work. The common ground on both sides had resistance and all injector solenoids were under 3 ohms so i replaced both gasket harnesses with no improvement. I then found where the external plug for the driver side UVCH had a couple bare wires that looked like they might be rubbing. I replaced this plug and the truck wouldnt start on the first try. I finally got it started and it runs like total crap now. I double checked to make sure i had the corresponding wires connected correctly and everything looks right. The CEL is on now (it wasnt before) throwing lots of strange codes. I am going to replace that plug again Monday because it is Dorman instead of FoMoCo and might be defective, but looking for more theories?? Any help is greatly appreciated.