The gas milage on my 99 4x4 Reg cab 4.6 automatic has dropped off the last couple of tanks from a consistent 15.5 to 16 mpg to 12.5 - 13 mpg. No change in driving habits or routes. Using same Texaco Hi Test gas from same station. Truck has 9K mles. Have been running a SuperChip, Gibson catback,K&N filter, and mobile 1 5w-30 since 2K miles. Could this be the K&N filter affecting the Mass Air Sensor? Thanks in advance.

BassDean

 

How dirty is the K&N filter?

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99 XLT 4.6 midnight blue reg-cab, Airaid K&N, dual exhaust

 

I think its not so much the K&N as it is a combination of the other mods. I have the same set up as you and have not had a drop in MPG, in fact mine has gotten better. I use 93 octane consistently and usually get the following gas mileage:

Highway/City=15.5
Highway = 16 to 17

I have heard that these engines do not respond to the mods you have done the same as the pushrod engines.

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The Truck: 1997 Black F-150 Flareside. Regular Cab ORP and Towing Package
The Mods: K&N Filter, Eurolid Hard Tonneau and Ford Bug Deflector.
The Site:
Triton's 4.6 Liter Web Page
www.mindspring.com/~acbradley/index.html

 

K&N Filter is clean. All mods were done at the same time when the truck haad 2K miles on it. Why would a change just occur after being consistent for 6k miles. From reading the post at this board the mods made seen to be the most common / popular upgrades. Just asking the question before starting to "back out" the mods or taking the dreaded trip to the dealer. Thanks for the input.

BassDean

 

Depending on the region of the country you're in, gasoline formulations are sometimes changed for the winter. Your drop seems rather large for just that though.

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99 XLT Black Ex-cab, Flareside, 5.4, ORP, 3.73, Gibson Supertruck, K&N, Superchip, Raised front 1", Modified Airbox, Slap-Free Motor at @19k

 

yeah, that's what I was going to say... if you live somewhere that gets considerably colder in the winter, that could make up for it. The denser air makes your computer deliver more fuel to compensate.

Otherwise, you could have a problem in your ignition system... if one of your spark plugs or wires is bad and isn't firing, then you're not running on all cylinders, so you have to give it more gas to get the same desired amount of power, while the unburned fuel goes out your exhaust pipe. Check your plugs and wires.



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-cm

 

Thanks for the input. Checked the spark plug wires and everything was tight. Also ran the motor and did a visual in the dark to check for any arcing, was none. Removed the K&N filter and checked again, looks OK. Also checked the intake pipe, it was absolutly clean. You may be right with the formulation change of the gas. Will try several more tanks of another brand and see if any difference. In the past I have had best results with the Texaco 93 stuff.

BassDean