03 7.3 rough running issue.
I thought I'd throw this out to see if anyone could point me in the right direction, maybe something I've overlooked. Sorry in advance for the long post.
I'm helping my brother with an issue that he is having with his 03 F250 7.3L. The truck is completely stock with 88,000 miles on it. The problem started a couple of months ago where the truck started running rough and low power while driving and idled rough. I used my Autoenginuity scan tool to see what was going on. I found cylinder 1 and 3 where failing the cylinder contribution test and a IDM failure code. The truck also exhibited hard starting with ipr being commanded 65% and taking about 7 seconds to start building icp. Once running they both looked normal. I checked the under valve cover harnesses and engine harness visually and through the pinpoint test from the IDM connector and they checked out ok. I found no chaffed places on the harness. So I decided to replace injectors 1 and 3. The truck ran great for about 500 miles and then started to do the same thing again along with the hard starting issue. I drove the truck and had it fall on it's face with the ipr being commanded 65% and very low icp. The PCM stored a P1211 ICP lower or higher than desired (Engine Running). I started checking the high pressure oil system and replaced the ipr valve. This took care of the hard starting and stalling issue. The truck now starts like a champ hot or cold, but still intermittently runs rough. I also have replaced the IDM since it did have a fault code, but it did not make any difference other than the code is now gone.
I have also looked at the fuel system. I have 55 psi at the test port in the head with it dropping only to 50 at wide open throttle. It did however a couple of times take 10 to 15 seconds to build pressure when starting. I cleaned the pressure regulator and replaced both check valves. I have also replaced the fuel pump. Pressure seems to be holding stronger now.
I have also done a compression test since that could also cause cylinder contribution codes and found all 8 cylinders between 400 and 420 psi.
Now after all this, the truck still has the rough running issue which comes and goes. Autoenginuity shows everything normal whether it's running bad or good. Cylinder 1 and 3 is still showing 3 to 5 percent deceleration and failing CCT. It was doing this even after replacing the injectors. I'm now at a loss and hope someone out there has seen something like this before and can give me some insight on what is going on. Thanks again and sorry for the long post.