We have a 2012 Paccar MX13 six unit pump engine in the shop with fuel in the oil. Originally I pressure tested fuel passage in block and all six unit pumps had fuel dripping off them. So we pulled pumps, o-rings were not cut. Installed six new pumps. Just pumping hand primer I have fuel dripping out of #2 unit pump bore onto camshaft. Removed pump, o-rings were not damaged. Swapped pump with #1 and re-o-ringed both. Still leaking on #2. Removed pump and lifter found fuel to be leaking out of oil passage that lubricates pump lifter. Reinstalled unit pump without lifter and verified that for a fact pressurized fuel is dripping out of the oil rifle into bore for pump. Has anyone seen this? I'm leaning towards a cracked cylinder head at this point where return fuel from injectors is getting pushed into oil rifle to rocker shafts and draining down and out.

James Benedict
Technician
The Service Company
Greenville, Ohio, USA