So, here's the the story of the demise of the 7.3 as I heard it from a field service engineer. First off, it's a good engine, but our "gubment" decided the emmision levels were not good enough. Ford was working on the 6.4 design for a replacement, but still having a hard time getting it clean enough. Thus, the 6.0 was born. Smaller displacement and easier to clean up. And, they could have it out in time for the new standards.
When the 6.0 came out, people would ask about "hot rodding" them with chips, programmers, and such. Now the 7.3 was a big ol' engine which was basically detuned from the factory. It had lots of displacement. The 6.0 comes out with more horsepower and more torque. The only way to get more with less, is to run it near the top of its capabilities.
With the 7.3, you could throw in a programmer, add bigger exhaust, put in a less restrictive air cleaner, and rock and roll. The 6.0s didn't take as kindly to the mods as the 7.3. (Ford was already pushing these 6.0 engines to get the performance from the factory.)
Some 6.0s began to show issues. Mostly the earlier ones were wiring harness chafing, injectors and turbos.
Ford says to International, Thes parts you are building for us are failing. We need them replaced under warranty. International says, ok, here are some new replacement parts for your warranty. Ford ( and International ) finally found a way to make the 6.4 clean enough by using the particulate filter system. They had many less issues, but still had a few. Ford says, your parts are failing, we still need some under warranty. International finally says "it's you design not our parts." (International has gotten tired of handing parts over left and right, and it's costing them.) Ford says our design is solid, your parts are the problem. They have a little lawsuit to straighten things out. Ford wants some changes to the 6.4 engine during production. International doesn't want to change. "You have a contract for so and so many engines, and we are not changing until the contract is fulfilled"
Ford is thinking we need to control our own product. Thus the 6.7 design is born. It's 100% Ford designed and built. No International control. If they see a flaw, Ford can be much quicker to react, make changes, and make things right.
IMHO there is still no substitute for cubic inches. The 6.7 promisies to be a good engine. There are already ways to get rid of the DEF. (Not Ford approved, of course. You know the "gubment" is looking over their shoulder). The 6.7 gets quite a bit more fuel mileage than any of the engines before it. And, even better mileage and power with the DEF delete kit.
If you've read this far, you can tell this is a "narrative" only as I understand it. I don't claim any of this as definative fact, and have no data to back it up. But, it's my story and I'm sticking to it
