The problem started with rought idle.

so we tried to change oil and filter (we used 10W40).

problem did not dissapeare. ECM throws codes (low secondary oil pressure and cylinder balance problems).

We used flush oil (thin). Engine runds on flush oil really well, but when we put new oil filter and new oil, the same prpblem.

So today we disassemblied secondary oil system but found no dirt, carbon deposits, no internal leak

Originally Posted by Taildragon

I thought that all of the Navistar engines used by Ford were Powerstoke engines.

Nope.

Back in the 80's you had the 6.9L idi naturally aspirated v8 diesel. Shortly after they dropped the 6.9 and moved to the first Gen 7.3 (international harvester)

In 1994, half way through the year they introduced the idi with a Turbo system. In '95 they introduced the powerstroke name and it went from idi to di for more power and torque.

The power stroke name stuck. Navistar was rushed by ford and the EPA in 2003 to come out with an egr 6.0L and they came up with a lot of egr problems. Then they went to the 6.4L twin turbo engine in 2008. In 2011 ford dropped navistar and began building their own engines. They still have the power stroke name. In my opinion the true powerstroke was the '95-'03 7.3L

Ethan