Have a coworker with the 6.9L diesel in it. He is only getting 10-12 mpg. Is there anything short of buying another truck that can net him some mpg gains. He rebuilt the engine a fuel years ago and has put a new injector pump on it. Is the exhaust, intake, fuel system, cam the biggest weak spot on this year engine. I ask because I have heard many people with excursions that use the 7.3L engine. They get closer top 20.

 

If I remember correctly, the 6.9l is an N/A engine..(no turbo)
The 7.3l in the Excursions was a TA HUEI.
My F.I.L. has an early 90's 7.3L N/A engine in his 1-ton crewcab dually. Old truck will probably run forever, just won't get there very fast!.
Never tried to check the fuel mileage on it, due to the stupid flowback lines always leaking..

 

The old 6.9 diesel is a tuff dinosaur with no weak spots as far as I am concerned. Back when the speedo worked on my 85 F-250 10-12 was normal highway milage I have 4.10's with a 4 speed. 55 mph would get you 17-18

 

I would have the injection timing checked and check the fuel pressure from the lift pump. Other than that, not much can be done unless you want to go through the injectors.

 

The truck has a manual trans and non-turbo. I just thought mid teens would be reachable as a daily highway driver with minor tweaks.

 

Indirect injection is not very efficient, and I've heard the typical life expectancy of an injector on a IDI is 100K miles if you're lucky. This has proven true with all the old trucks at work, Chevy 6.2-6.5 and Ford 6.9's.

 

The info you have been given re 6.9 IDI is correct.

I have a 1986 F-250 (bought it new) with auto (C6) tansmission and 3.55 rear end. On a long run with a 21ft travel trailer or truck camper and 60mph max., I could approach 18 mpg (imperial gallon) - but my engine has an after market turbo on it. I put the turbo on at around 80,000km and now have 350,000km and the engine still doesn't burn oil leaks a bit now and then.

The bigger exhaust helps as does a modified air supply to increase volume. Fuel pump timing helps of course and if the timing was out, you would really notice a difference in power after the adjustment.

Good engine and a real workhorse. If you could get a used turbo cheap, that would help a lot.

mariner

 

Meet a guy with a 6.9, he was the original owner (1986) and he was getting 20mpg with 457000 on it.

 

No overdrive, how fast is he going on the highway? What rearend ratio?
I had a 6.9 for many years, if you try to run 70-75 the MPG's suffer big time.