gas mileage

I have a 99 f-150 with a 5.4, new plugs from ford (platinum), an engine decarb was done and fuel injectors were cleaned. The air filter box was cut out to resemble an open air element for a K&N air filter. Pirrelli scorpion tires 265/75/16. My gas mileage sucks 12 currently 13.5 in town and 14.75 on highway. When it was new to me 19K miles it got about 15 and 17 respectively. What gives with this. Do I need to enclose the filter box, it is the factory air filter housing but cut out for what I thought would be more cold air. I also have a flowmaster but mileage hasnt drastically dropped off until lately. Was pretty consistent until the tune up 13.5 in town that is.

Fuel economy is materially affected by:
-HEGO sensors
-Drag (tire pressure, ride height, wind etc)
-fuel quality

The first thing you must do when calculating MPG is find out EXACTLY how accurate you odometer is. A very easy way to do this is on a long streatch of highway (10 miles or so) and a GPS unit. The GPS will be within a few feet of dead-on accurate, does your odo agree?

Next, is the unit lifted, are air dams/deflector installed etc? Is the alignment good? Are the tires inflated properly? Are they good tires with low rolling resistance (off-road tires can reduce economy up to 25%).

Fuel quality varies by the season in MANY areas of the country. I nthe North especially, refinerys are required to add "oxygenates" to the fuel to reduce emissions during cold weather operation, this will reduce you econlmy by up to 15% by itself.

Fuel economy is materially affected by:
-HEGO sensors
-Drag (tire pressure, ride height, wind etc)
-fuel quality

The first thing you must do when calculating MPG is find out EXACTLY how accurate you odometer is. A very easy way to do this is on a long streatch of highway (10 miles or so) and a GPS unit. The GPS will be within a few feet of dead-on accurate, does your odo agree?

Next, is the unit lifted, are air dams/deflector installed etc? Is the alignment good? Are the tires inflated properly? Are they good tires with low rolling resistance (off-road tires can reduce economy up to 25%).

Fuel quality varies by the season in MANY areas of the country. I nthe North especially, refinerys are required to add "oxygenates" to the fuel to reduce emissions during cold weather operation, this will reduce you econlmy by up to 15% by itself.

The tires are low rolling resistance tire not lifted truck and I've been using 87 octane chevron or giant fuel and the odometer might be off by 2 miles low over a fourty mile stretch. What is an HEGO?

Heated Exhaust Gas Oxygen sensor. They play a very important role in economy.

Heated Exhaust Gas Oxygen sensor. They play a very important role in economy.

Dumb question time, Is this my oxygen sensor, is it soething easy enough I can do, what brand should I buy Ford or from a local parts store? What I'm asking is should I use a Bosch, Motorcraft, or NGK part. Should all the wires match up color wise and j plug be the same, I'm pretty sure I can do this myself. Do you have to be careful when removing the old one and do I need to use anti sieze on the threads of the new one. Tired of feeling like I'm getting ripped by mechanics. I'm an HVAC/Refrigeration mech by trade so I have a good mechanical backround, but I don't want to break anything else I'd have to fix. By the way I just replaced the front rotors on my truck what are the torque spec for the 18mm and 13mm bolts for the calipers and caliper housing bracket. I couldn't get these from the dealer or manuals I have.
I will try to post my fixes for steve as soon as I get my copy from the mech either today or monday. Thanks

Replacing the HEGOs is VERY easy. I use, and reccomend ONLY Ford/Motorcraft OE replacements. They cost a little more, but from my expieriences, they also last a LOT longer. They come with the connectors attached, so they are "plug 'n' play".

ONLY the two FRONT sensors affect economy.

i think bosch makes a better part in this case. o2 sensors are o2 sensors, they usually plug up with carbon and other crude and last anywhere from 80k to 100k.

No, Bosch DOES NOT make a "better part". I know of MANY people who have installed Bosch HEGOs in replacement of factory Ford parts, and not one has been satisfied with their longevity.

And no, HEGOs are not HEGOs, any more than a spark plug is a spark plug.

I agree with Modtech. Tried Bosch plugs, they suck. Replaced O2 sensors with Bossh, they lasted about 20K and also killed the fuel mileage. Went back to Motorcraft, mileage went back up to the low 17's.

This sounds far fetched, parts guy said to remove o2 sensors and did them in ice water it would crack the carbon and make them cleaner. I don't put much faith in that idea though; if it is just a sensor though can you clean it with electrical parts cleaner or brake fluid since they shouldn't leave a residue? If not I'll but those O2 sensors, the parts guy also said I needed a calibration code; where do I find that? Thanks for the help guys.