wiseguy
Member
I have a problem child I am having a hard time figuring out. back gound truck s an 04 f550 service truck with abut 200k on it but has ton of hours pto has over 16,000 on it. Over all the truck is a turd that has been heavily molested. Anyway truck was towed in crank no start truck has about two pages of dtc's. anyway check fuel pressure 30 psi ficm voltage 26v has 1700 icp relative compression 2%. So i started with the obvious new lift pump blue spring kit and bpd ficm power board also repaired wires to vgt actuator oil switch and eot . Ok re test koeo pass yea! now i got 49.5 v 62 psi fuel hit key fires up well sort of runs rough power balance looks bad miss on several cyl as warms up clears up i ran it down the road over 2500 seem to run pretty bad cant really id specific cly except cyl 3 keeps missing. After i drove it now has contribution codes for cyl 3,5,8 and cam sensor code. So i finally decide it needs a new set of injectors. Ok so i pull it down replace all 8 injectors when i went to replace #7 I noticed the connector was melted ficm connectors are already zip tied so i also installed new ficm harness. I replaced the cam sensor and conector i also had to repair several wires i noticed that were worn down to the copper where they had been rubbing. ok lets try this again koeo pass hit key fires up runs nice smooth down the road runs perfect under 2000 rpm get up to 2500 seems choppy looking at power balance best i can at higher rpm i cant id any specific cyl? only dtc i have is for egr flow p401 i know that's not an issue it does not have a cooler. So I pull out scope and try to look at ckp signal i can see the stutter but looks more like a symptom than the cause signal is there but time changes???? I'm stumped so i start guessing the harness looks bad i already had to repair a ton of wires so i swap the whole engine harness from a parts truck i had while i'm at it i change the ckp sensor. My thought maybe i'm missing something. I go drive it runs perfect well not really as it warms up i notice it gets choppy kinda stutters at high rpm still WTF?? ok no codes 62 psi starts perfect runs perfect cold.. I notice if i rev the engine sitting still in park i can feel it. If i run power balance as high as it will let me it looks like a random misfire.. electrically i changed most of it so i try a different known good pcm off my 04 parts truck and also swapped to different ficm still does it. I also tried unplugging the icp, ebp, map, maf, eot, vgt egr, alternator and throttle plate basically left it down to bare minimum rev it up still stutters.....So now i'm really lost I'm pretty confident i eliminated a electrical issue. Only other thought i had is something in the valve train. Gassers will miss at higher rpm with bad valve spring. but hat is easy to check with vacuum gauge on gas not sure on a diesel. Only other thing i noticed base fuel pressure flickers about 2 psi when it stutters, pressure actually goes up slightly, pressure and volume check good fuel quality seems ok short of sending it to a lab. Any one have any ideas? i Have been working on this for two solid days now i just don't know what else to check.:wtf:
