Gas Mileage Help (460 EFI)
 

My truck is a 93 F250 Reguar cab with a long bed. Im running stock sized wheels and a 4.10 rear end. The truck has a had a full tune-up (spark plugs, cap rotor and wires, cleaned throttle body...).

The only upgrades it has is a banks ram air intake, magnaflow muffler, and a banks trans shift kit. I run 91 octane fuel too.

I have the E40D but dont use overdrive unless on the fwy. I drive 45mph or less on city streets so it saves my trans. I take off extremely slow and never really drive fast. I still get 6.5mpg with an empty truck...does this seem correct or is something wrong?

I changed my EGR already so i know thats not the problem. What can be the problem? I expect around 8mpg???

Thanks in advance

Have you checked for codes yet? Even of the lights not on there still may be codes there

Yes my Dad has a Snapon Code scanner and no codes are displayed. It just says that there might be too much air flowing through the engine for the EGR to fully work but ive heard of penty of people with aftermarket exhaust and get better mileage than I do???

Slow starts an 6.5 mpg, theres something seriously wrong with an empty bed

2 problems.

Use the lower octane fuel. Higher octane REDUCES milage.

Use OD. Just let the auto be where it wants to be, it will down shift if it needs to.

With 4.10 gears you truck is going to be using OD a lot even in city driving, and if you want something that could be confused with fuel milage you're gonna have to let it use it.
That said it's still possible your truck has a problem, does it have dual tanks and if so do they both work? There is a common problem where fuel is transferred between tanks as you drive because of leaking check valves inside the tank, if you have a tank that doesn't work you may never notice anything except an occasional fuel smell immediately after stopping, while if both tanks work you may notice that a previously empty tank now has fuel in it after running on the other tank for a while. Other potential caused of bad fuel milage are a leaking/faulty fuel pressure regulator, check the pressure on the rail with a gauge(should be 40-45psi with vacuum removed from teh regulator), and there should not be any raw fuel in the vacuum line or leaking out of the vacuum nipple on the regulator.

You just contradicted yourself. Plus there is no code with the definition you listed. Please give us the error code number and when it occurred, i.e. during KOEO tests or from CM (Continuous Memory).

Well there was no code, but under the troubleshooting guide, thats what it said. we were trying to get the EGR to work properly. No code was ever displayed.

Thanks again for all the input! I will check it out and let you guys know the results

if the truck is a 2wd,a cheap mod would be to swap in a 3.55 axle from a local salvage yard.
next,a lot of folks focus on motor mods for increased economy with trucks.when it comes to trucks,nothing can touch aerodynamic improvements.
forget what you have read about auto transmissions and using OD.you will not increase it's life by running in 3rd gear instead.
you just don't want to let it "hunt" (shift back and forth between 3rd and 4th,inside just a few seconds) besides that,let it shift on it's own.with the low end grunt of diesels and 460's,your not likely to have trans "hunting" issues at all (iv purposely tried to make mine with the diesel,so id learn it's point where id need to lock out 4th.i can't make it hunt between gears even trying.)
you can also buy a good quality aftermarket low stall torque converter to help some.
lastly,don't expect the world.460's are very well known for being very thirsty engines.
id strongly suggest a small car for running empty,and saving the truck when needed to haul/tow stuff.just a suggestion.it's not an option for some.
again,focus on aerodynamic improvements.nothing you do to the engine will ever compare to the gains.

according to my personal field tests over the years with various cars/trucks,iv always seen just the opposite.
important note however: i have never owned a 460 gas engine.

I've found the same results with my 351w in my truck, and the 2.3L in my brothers ranger, as well as the 4.6 in my Thunderchicken. My truck gets 1 mpg better with 93 octane over 87. And my Tbird gets 2 better. The ranger gets about 4 better. But the little 4 cylinder in that just barely sips fuel anyway.
But, I don't have a 460 to use in a comparison either.

On the higher octane fuel I have to agree with the others that have said it's an increase in economy over 87. I've experienced the same thing.

As for the 6.5mpg in third gear your transmission is in 1:1 ratio. That means for every 1 rpm the engine turns the drive shaft also turns 1 rpm. Fourth (OD) is .73:1 so you get ~25% reduction in RPMS, so if you're turning 1000rpm at 40mph in third you'd be turning only 750rpm in OD.

I can get 14 with my 260K 460/E4OD/3.55 4WD F250 with 285/75 tires (yes PSOM is corrected) IF I drive like you describe. More throttle or heavy towing can easily drop to 10.

i get around 10 with my flatbed 4x4 dually with 460 zf 5 speed 4:10 gears loaded or empty