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OK now I'm sorry o brought it up! As I stated its only 2mpg I don't care it just had me puzzled. I don't care about fuel mileage as I'm sure most of us on this site don't, if I did I would own a sailboat and a Prius not a 32' twin engine gas hog & diesel truck.

Your fuel consumption with diesel will change with temp changes, it effects my 2 fords and 12 internationals. Just glad to be paying in the 2.00- 3.00 range again.

Make sure your not spinning the front axles. Lots of issues with the hubs in those newer 7.3 trucks. Oil changes /fuel filter changes are very important. Use synthetic oil it's easier on the injectors. When I do a filter change on one of those trucks I drain the filter housing and dump straight diesel 911 in the housing. Start it up let it smoke and blow it down the road it does a very good job of cleaning things up. Some of the 7.3 truck get good gas mileage some don't. They put different rear gears in them. The ones with the 4.10's are terrible on fuel mileage.

I have a 2000 Excursion 7.3 4X4. Pretty similar to a F250 pu in size and weight. My diesel mechanic advised me if I put a chip in it and increased the HP from 250 hp to 300 hp I would pick up 2 mpg on the highway. Amazingly he was 100% correct. I did go from 14.5 to 16.5 on the road, not towing and running 70-75 mph.
My truck has stock wheels and tires and stock ride height.

2002 F350 4wd 6" lift 35" tires got 16-17 empty, 13 towing 7500lb boat.
2002 F250 2wd stock suspension 20+ empty, 14-15 towing same boat (this truck has the full Banks Powerpack which is the only way to tow with a 7.3 IMO)

Quote:

Originally Posted by bigredbaja (Post 4366247)

I'll try answer all the questions at once....its currently due for an oil change I have 5000 miles on the oil and I have been running Shell Rotella oil, tires are 35" and properly inflated the computer has not been adjusted for the larger tires (don't know how to do that). The fuel filter has maybe 5000 miles on it but it seems like my 14.5 is not to far off. I will change the fuel filter again when I change the oil this time and add an injector cleaner.

What kind of tune/programmer is on the truck?

If its a piggy back style that plugs into the OBD-2 port, that wont correct it in the ECM of the truck.

If you have the flash style with a handheld programmer, you can adjust the tire size with that. Plug it in, find where to change the tire size settings, change them and then reflash, good to go.

If its a custom tune done by someone with aftermarket tuning software, you would need them to reflash the ECM with a new tune with the adjusted tire size.

The ECM seeing the wrong tire size is going to make the speedo, trip, and mileage (miles not fuel mileage) be off, just letting you know.

^^^Yup.^^^^

Larger tire will make speedo read lower mph. So, of course your odometer will read less miles than your actually going. So therefore, your fuel mileage will appear to be less than what it actually is.

If you want to take that further, if you drive the same indicated mph you did with the smaller tires, you are actually going faster than you where with smaller tires, which in of itself uses more fuel.

Even further...most larger tires are more weight than the smallers. More fuel use. Compounded, tires are unsprung weight, which means the actual added weight's effect is larger than the weight itself. About 10 times more. Yup, no schit.