6NZ overhauled, but number 5 piston keeps getting fried!

Appears to me the shop performing the overhaul might be missing something, or not overhauling the engine right. A constant cylinder getting fried most often with the C15 (6nz) is caused from injector wiring issues or tuning problems (if you have it tuned). I would do injector tests individually and have the wiring diagnosed. This will most likely weed out any issues.

 

Forgot to add to original post; if you have a diagnostic done and codes are present either active or stored, and fault code 74, SPN 5 and/or FMI 11 pop up that signifies an injector current fault. The SPN number signifies the injector number. Code in your case may read as: Fault Code: 74 SPN: 5 FMI: 11 depending on scanner used.

 

Fried how? Got any pictures?

 

My guess would be an injector issue or possibly something like a restriction in the galley to the cooling nozzle.

PS we like pictures!

 

Part numbers would be nice as well. Could be a mismatch

 

how long between failure? are they fitting the cooling jet AFTER the piston and rod?

number 5 and 6 generally run pretty warm with a decent boost leak. often its enough for the factory articulated piston to grab the skirt. check the CAC system for leaks by pressurizing it.

if number injector is the incorrect part number or has an excessively worn tip that can also do it.

cat REMAN liner packs are horrendous. if you ever measure up a piston skirt and liner you'll be appalled by what you find. they're often out of round or oval in shape by several thou.

I personally only use new cat liners for the above reason. I also use a steel one piece piston, again so the factory aluminium skirted piston can grab and scuff the skirt.