took a road trip today, about 300ish miles one way. So i figured i'd take a look at the fuel economy of my 4.6L. i drove 68-70 MPH and used cruise control thr whole time. The truck is bone stock except an airbox mod with a K&N. i am running full synthetic mobil 1 oil. I also have a CEL for the egr crap. New components on the truck are fuel filter, air filter and plugs and wires. on the way home i did have 4 17" rims with tires mounted on them in the bed. I do have a tonneau cover so i'd imagine that helps with drag.

200.1 miles running 91 octane got me 16MPG (filled at half tank had half a tank of 89 in prior, with a bottle of lucas fuel treatment)
165.2 miles on a fillup of 87 octane got me 13.2 MPG, about 20 miles of city driving here. also you could say i was running 89ish because mixing 91 and 87 equally will give you 89 octane(thats how the pumps make 89 at the gas station)
the next 145 miles i ran 93 octane and got 23.2 MPG

 

which way was the wind going?

 

it was actually really windy and i was driving out in the middle of nowhere. but mostly from the north, i was travelling east/ west.

 

why are u using such high octane u only need 87 in it. and damn i get 17-18 highway with all my mods. sounds like u need a good tune up

 

i used different octanes to see what kind of mileage i got with different octanes.

and since you asked...i did say i have a CEL for the EGR, meaning the PCM is likely running in generic mode which = crap mileage anyways.

 

Snake oil and the wrong gas .. Really dude , you don't need to do that. You doing more damage then good. Stick with what the engineers designed the motor to run on . They know more than you or I do .

If you google search that out - the reasons why are out there..

It all comes down to - updated O2 sensor's, healthy ignition system and a clean throttle body (elbow and ports).

AND - the way you drive her of course..

 

yeh dont be afraid to give her a good WOT run once or twice a week to keep the carbon off

also id ur thermostat stuck open?? that will effect the fuel tables. and kills ur fuel economy

 

there is possibly some problems with the T stat, but nothing bad as the temps are ok. the only thing telling me the T stat is going to go is the clutch fan, it surges alot (like every 3-5 seconds). but until i get this EGR thing out of the way i cant be sure its not related to that.

 

There is no point in messing around trying different fuel, additives, and measuring gas mileage till you get the cause of the CEL fixed.

 

im aware of that glc, however the lucas additive was because when i changed my fuel filter the inside of it was nothing but brown rust and chunks(previous owner NEVER changed it, it seemed) so dumping a fuel system cleaner was kind of needed since im sure a chunk or two found its way through my fuel system and likelyclogged something up. the reason for the different octanes was so i could see for myself what kind of mileage i was getting. Having a CEL on only means my gas mileage will improve when it gets fixed.