Engine Misfiring?

[SuicideAxles]

My buddy just got a truck nearly identical to mine to use as a daily driver since he popped the motor in his old daily driver '59 Apache. The only real difference is that his is a regular cab. It's a '96 F-250 5spd 4x4 with the 7.3 PSD and 190k miles. It seems to surge or have a slight misfire at idle, or maintaining low speed. Its more noticeable when the engine is below operating temperature, but you can still hear/feel a slight misfire at idle. When driving 30-40mph and maintaining speed you can hear the engine sound like it has a slight miss. We just replaced the fuel filter, oil & filter, air filter, hoses, belt, coolant, fluids in T-case and both diffs. I figured maybe it was a clogged fuel filter, but the 'tune up' didn't change anything.

Any ideas?

[djsdiesel]

get somebody with a scanner. Have them run a cylinder contribution test. Maybe bad injector. When you changed the fuel filter was the inside of the housing black?? If it was it needs injector o-rings.

[DirtyDiesel]

same problem with mine i would also check compression. mine has 180K and one cylinder is 50psi short on one cylinder.

[Diesel_Diagnostician]

Check valves can cause misfires as well...watch for the black goo in your fuel bowl...may not be "oil" can be a mold (kinda looks like tar), caused by humidity, oxidation and water in fuel, wear rubber gloves....you can get sick from that stuff....