79redtruck

1996 F250 Crew cab, short bed, 4x4 with the 460 and E4OD trans. I have put the full banks kit.(headers, y pipe, muffler and tailpipe). K&N air filter, flex a lite electric fans. First time out of the shop the truck made 17.6 miles per gallon. After a few trips the milage strated to drop. 15 then 12 then 9. Put in a new O2 sensor same thing. Changed plugs, wires, cap and rotor. Same thing. What am I missing.

Thanks Puzzeled

Bert

If it's the light duty model with the MAF sensor, the oil from the K&N can coat it with oil and the PCM won't get the correct reading. See what codes might be present. Autozone will check for free.

__________________
Bert

chipset

Throw the K.N. in the garbage. We've returned 3 of them after we found sand in the air
tubes. They only work at W.O.T.

Bluegrass

A cause could be that the EEC/PCM was powered down for the work.
All the tables were zeroed back to stock baseline values.
As the EEC learned the new setup, it shifted them and settled down to what you now have or your running on a custom program.
I don't think it will get any better.
Power cost fuel, air and money.
The changes you made are not going to add better fuel mileage for normal truck use over stock where the stock equipment was good enough.

Why would you expect to get better than the same mpg of a stock motor?
Changing the air tract is not going to add any more air flow except at high RPM.
Reason is you need to remember the throttle plate in the throttle body dictates the amount of air that is injested at any RPM, not the air filter, or exhaust.
Had a guy come on another board to tute his mods and said he got 27 mpg.
Think any body believed it out of a normally 15 mpg truck series with a lot smaller motor than yours?
Good luck.

79redtruck

The truck is the heavy duty model. The truck also has the trans command. I am not bragging about the truck. I am just hoping to find a solid answer.

Bluegrass

What was your mileage before the changes?
The only change that would have any effect is the electric fan setup.
They would relieve the engine of some small amount of drag from the fans.
Otherwise the electric motor/s will take power from the alternator that is still driven by the motor so the fan is still not free power but just a lesser load.
The only solid answer is, your expecting something that is not there to get.
On to an example; My completly stock 4.6 super crew pulling 12,000 gross combined weight got 9 to 10 mpg over 230 miles round trip to the race track.
Your motor displacment is 1.75 times larger and will take more fuel just on engine size alone besides the weight of your truck is likely higher.
Best ive been able to get, driving 55 with very light foot is just over 17 empty.
Good luck.

dj speed

I think you will only gain 1 or 2 mpg with those mods if you are lucky. I dont know how you calculated all your other numbers but you are not gaining 7 mpg. Did you change the size of the tires? That would affect your odometer readings.
Okay never mind mpg, how did the truck feel with all those mods? Did it make a noticeable difference in performance?

360ci

460ci engine = lucky to see double digit mileage.

You can try disconnecting the battery for an hour so the systems can 'relearn' everything and hope you'll gain better mileage. I get 11mpg city with my 5.9L V8 Durango, but I didn't buy it for mileage; it's for towing and hitting the trails.

Most newer V6 and small V8 half-ton trucks are lucky to average 15-18mpg. I'm lucky to average 14mpg in my Durango (with 75%+ highway miles). If I drive at 60mph I can reach 16mpg, but only if rolling hills are used to my benefit.

Best thing you can do to decrease some friction and heat, and perhaps (perhaps!) gain some mileage is to use full synthetic fluids in the engine, transmission, pumpkins, and transfer case. If anything you can drive a lot farther on synthetics, which alone is worth the added cost and downtime over standard petroleum based fluids.

Other things is extra weight in the truck that's unnecessary, tire pressures, brake caliper sticking (increases drag), and so on.

__________________
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!