d12 compression problem

hey everyone. i rebuilt a 2002 volvo with a d12c engine last year. it started perfectly. ran smoother then any of our other fleets trucks. the truck originally cracked #3 piston liner, and #4 looked terrible. we have 10 used decent liners laying on the shelf. so i had swapped 2 used ones into 3 and 4.
the head was rebuild by a known shop, most valves guides and seats were replaced. rod and crank bearings replaced. all new piston rings also. and any other gaskets or o-rings.

he finally took a week long trip. (previously no issues on local trips and 400 mi trips). but he came back misfiring and with white smoke. codes read 4th injector mechanical fault. and zero compression in cyl 4 and 75% in #5.

can an injector cause no compression? or does that sound more like a head gasket?

i havent done any other diagnosis yet other then the two tests. will be taking the valve cover off soon for a visual inspection, and also checking for fuel in the coolant and oil.

any other ideas?
thanks!

 

well no coolant leaked out while driving, i can somewhat assume coolant didnt get cylinder pressure.

ill be taking stuff apart today

 

another thing. it runs smooth for the first 30 seconds of startup. even at 160* coolant temp after sitting for an hour

 

i ran another compression test. #4 now has 93%. #5 still at 70%.

started the truck, it ran good for 1 minute, until i hit the throttle. instantly started missing and smoking. definitely confused. ran it without a valve cover. everything looks good.

 

just took rockers off. looks like piston wont go all the way back in on exhaust rocker #4. gonna swap it out and pull the injector to check it too.

 

well fixed the rocker piston. it started to unthread internally. #4 cyl is now good. and 5 still low compressionafter swapping injectors. just gonna put it together for now