Welcome to TheDieselStop, Mary

The 7.3L uses high pressure oil to operate the injectors, and problems starting when hot are generally caused by leaks in the high pressure oil system. Could be the IPR (Injector Pressure Regulator) sticking open, preventing pressure from building up. More likely is a leaky injector o-ring, either into the fuel gallery or into the valve cover area. A small leak won't be enough to prevent starting when cold, but as the oil warms up, it can get thru the hole easier (faster), preventing the pressure from building to the 500 psi minimum to start. Could also be an external leak. Check in the engine valley on the hoses that run from the HPOP (high pressure oil pump) to the heads.

Hope you can get it figured out.

 

The first thing most will check for as stated is for leaks in the hpo system.

When it starts fine when cold, but not hot, the first thing most people will inspect is the IPR o-rings.

 

We have an answer-yes it was the IPR-o rings. He wasn't too happy to tear in to this project, but in very short order, he came "waltzing into the kitchen" to show me the broken o-rings. Had to cook him up something extra special for Father's Day!! Thanks for the super quick responses and great suggestions. One last question though, how often, if at all, do the fuel injector o-rings fail? This diesel only has about 140k on it.

Hope everyone had a great weekend.
Mary

 

One last question though, how often, if at all, do the fuel injector o-rings fail? This diesel only has about 140k on it.

Normally they last a long time. I was at about 190k before I upgraded to aftermarket injectors, and my original o-rings were still good. Some people have had them go a lot sooner though.

Justin

 

Best sign of O-ring problem is black sludge in the fuel filter.

Steve