Hi guys, I have a 97 f-250 HD with the efi 460 and E-40d trans. It has 116,000 on it and runs great. All I know is when I got the truck about 6 months ago....I could fill up the front tank which is 15 gallon. I could go 145 miles on that. (I knew it wasnt a cobalt). But I put some upgrades on it which gave it more power I think. Oh it is 4 wheel drive with manual hubs also. I put a cold air intake on it, a throttle body spacer, deleted the mufflers ,and left on the huge cat convertor, straight pipes out back, from the convertor..(2 and a half). I also put an MSD coil on it. I run Autolite plugs, and a decent set of wires. My question is , now on that 15 gallon tank, I only get 125 miles on it now. I thought these small upgrades whould give me better gas mileage. As I estimate, I think i am getting like 8 miles too the gallon, and didnt even stert the 4wheel drive for the winter.
Are my calculations correct, and is this truck that much of a gas guzzler.
Is there something I did wrong with the aftermarket parts.....could the timing be off?, could my convertor be clogged? How do you set the timing on this bad boy....wheres the tab?......So many questions....how long do these motors last for mileage wise?.............UGGGGGhhhhh...........Any answers too any of these questions would be greatly appreciated.
Thank you very much

 

I get 10mpg or less with my 89 F250 4X4 460 C6. From what I have been able to research 10mpg is about as good as it gets. Maybe 12 if you are really lucky.

 

Thanks...I figured

 

I've got a 92 4x4 crewcab with the same motor/trans. I was getting about 11.5 mpg in mixed driving but when I removed the K&N open element filter kit (too loud) and the electric fan (overheated easily when towing) and went back to the stock fan and airbox I lost about 1.5-2 MPG. So it seems to me that you are just a little under where you should be. I'd recheck your timing, reset your computer (unhook the battery for a few minutes) and see if it helps.

How loud is it with the cat and no muffler?

 

First thing.. you cannot use the gas gauge to calculate milage.
Second thing.. are the tires stock size?
Third thing.. is the truck Mass Air?

Even if the tires are stock you should verify the speedo is close to actual by comparing it to a GPS. If it isn't recalibrate the speedo by either installing a differnt speedo cable drive gear(on trucks so equipped), or by resetting the PSOM.
Now you can get some accurate milage numbers. Fill the tank and reset the trip to zero and drive until you need gas again. Now fill the tank again and record how much gas it takes and how far it went, milage is simple math from there.
If your truck is mass air the conical air filter you attached to the MAF meter is partially responsible for worse milage, fan wash creates air turbulance across the airflow meter and throws it's measurements out of wack. On top of that you actually now have a hot air intake because the motor is pulling air from inside the engine bay instead of outside via the stock airbox. In the winter and on cooler days this won't make much difference but in hot weather it will kill power.

 

I see what all yous are saying and I guess I am answering everyones questions.
OK with the muffler deleted....no difference in sound....huge cat takes care of that I guess.....Yes I did reset the comp., .....the cold air intake, yes the same in cold and hot weather.....and yes the skinny pedal...I do stay on it or off it, one time I beat the snot out of it, burnouts and all,...and then I drive it normal too the store too get beer, haul around heavy stuff, pull my race car....all mpg the same.
I just feel that something I did killed the gas mileage. OH and it does have the original size tires.
I am still wondering about that cat convertor......116,000 miles, wonder if it has ever been changed....Is there an easy way too check a cat without taking it off and driving it.

 

How does it sound with the straight pipe from the convertor? I was thinking of getting rid of my muffler and running a 2.5" or 3" pipe straight back fromthe convertor, but don't want to make too much noise. I perfer quiet over load.

 

I'm not expert, but it makes sense to me that if the cat does have the full mileage on it, and is near the end of its life, and you put in more fuel/air, it doesn't have the increase in exhaust efficiency to allow the engine to breathe better. so you're cramming more fuel/air in, but straining to get it out, reducing the overall efficiency.

 

Too pwjr....thanks, I think im gonna change the convertor definately.
And too jadmt, an actual muffler shop I took it too....(I told them i want dual exhaust,), they told me that these trucks sound cool if you just run the straight pipes back off the convertor. I did it and is still very mellow. MY advice is take the muffler off...trust me it aint that loud. I know a couple of guys that are doing this on mustangs and firebirds, and a lot of other newer cars...(thats where I got the idea)......them cats really quiet a car or truck. Just take your muffler out...you wont be dissapointed. Actually I think mine is still too quiet, so wanna go to a high flow cat.

 

I get 10-11 mpg. K&N air filter in stock box and Magna flow cat back exhaust.

 

I have a '97 F-250 HD 4x4 OffRoad SuperCab Short Bed w/ 460 & 5 spd, 130,000. I run mid-grade from 76 and get 11.2 mpg. And barely any of that is highway. I am running stock... ...everything.

Now the 460 / E4OD in my Motorhome is a totally different ball of wax. LOL



'97 F-250 HD XLT SuperCab 4x4 O/R 460 - 5 Spd
'96 34ft Fleetwood Bounder 460 - E4OD
'68 F-100 Custom Cab on '78 F-150 Ranger 4x4 Frame 390 FE - C6

 

Another big factor is what size tires you have. When I posted earlier I mentioned my airbox and fan, but I forgot that I went from 235-85 pizza cutter tires to some 285-75 all terrains. Less than 1" taller, but about 2" wider, the tire change alone cost about 1 mpg of the 2 mpg that I've given up since I got the truck. At least I don't need to go to 4x4 at the sight of sand anymore..

 

I got a 92 f250 HD super cab, longbox E4OD and the dual tanks. I thas 3.55's with i believe 235/85r16's. It is 2 wheel drive. I am getting about 14.5 including city driving and i took out the old exhaust from the flange back. Bought a new flange that went to 3" and stuck a thrush Glasspack on it that split to dual 2.5" and put a 27" pipe on each side that pointed down and called it quites. I took out the cat. But i also have an access tonneau cover on it. Those two improvements got me an extra 4-5 MPG's for about $800 where i live. I hope this helps. Best of luck.

 

97 F250 HD 460 e4od 4.10 110k 4x4 supercab shortbed stock, city-highway mix of 8mpg, been that way for 2 years the highest it has ever been was once i got 10.5 after driving down hill with a tail wind.

 

What gears do you have in the truck? I would also get rid of the cat or get free flow ceramic one from dynomax if you require a cat in your state. My truck has 385000 km's and it has never had any work on the motor.