1lw losing prime

Something to look into that does not cost anything is the 2 check valves that hold pressure to the pump when the tractor is sitting. Does the truck run ok when your driving it? If it runs fine, and only acts up when sitting then def go there first. The rubber cups on the valves could have a tear or the spring is letting the fuel run back into the tanks when the truck sits. It's a fairly cheap fix. A lot cheaper then doing a head. I'm not ruling out what your tech said. But if it is the injectors letting the fuel go you will have other symptoms. Excess smoke is a big indicator.

 

How does it sound once running?
Could it be losing prime from the return check valve?
Common to have slight leak out of fitting out of back of head which will loose prime very slowly.
Does it have new or rebuilt injectors?

 

The smoke and stumble is normal for air in the system.

Isn't it fun to go over someone else's work.

 

does it keep taking out the o-rings on the same injectors? has it been doing this since the head has been replaced? I had an engine do this some time ago it would take out injector o-rings on #3 and #5 the o-rings looked like a mouse had been chewing on them. I had two years of documenting the issue always the same two injectors. I kept telling my cat TC the head needed to be replace he kept telling me I was installing the injector wrong! ARE YOU KIDDING! just this truck and just #3 and #5 injector. finally got a hold of his boss and told him the issue. My cat TC call me told me to get my customer back in and replace the head cat would pay the ticket. The root of the problem is the injector cups being at the hi and low end of what is in specs created a turbulence in the fuel eroding the injector o-ring. A few months later cat released a service bulliten addressing this issue.

 

It happened to my friend's 6NZ. He took his truck to a local CAT and they re-machined injector seats without removing a cylinder head. This job was done last fall and till now no complains...

 

Manasteel, did they have a reason for the #3 and #5 going bad or just luck of the draw?

 

No reason for #3 or #5 specifically but I do remember that the injector cup height was all over the place. My cat TC never stepped up to the plate to tell me why cat agreed to pay the ticket. I met a cat fuel engineer at dinner one night and started talking about the issue I was having with this truck. He gave me the number of the cat rep that could set things right, and he did. My cat TC no longer speaks directly to me either. Im sure his ### or ego was sore for quite awhile. Much thanks to having a beer with the guy wearing the cat shirt that night. (that just sounds wrong)