hey everyone..its been along time since ive been here.
i know this topic has been beaten to death here but it seems my mpg is gettin worse.if i baby it(all interstate,60mph,no passing gear)i can get 310-320 to a tank full(28gal) but typically i get 10 mpg and it seems to be dropping.i believe the fuel filter is the original one and being located in the tank....well..im not to excited to change this.that and the fact that its all one unit(filter and sending unit)so its probably 300$?
i know my tires are 2 sizes too big and that certianly doesnt help.i did a tune up on it when i 1st got it probably 20k mi ago.
work has me driving 40 mi one way everyday now and this is killin me.
i have a k&n and a cherrybomb that i found layin around installed on it.
heres another issue i have....
i can fill my tank up and get 100miles in before i reach 3/4 of a tank.that being said,one would think that i could get 400 miles to a tank full.no deal.170 at half full,220 or so at 1/4 and ends right around 260-280 before i need to get more.i dont understand.
any thoughts?
thanks for listening.

 

Have you checked to see if the Plenum gasket is leaking?

 

Are you sure you have a 28 gallon tank? My 01 has a 26 gallon tank which I believe is standard. I get about 270 miles before the "low fuel" light comes on. I can then put about 22 gallons in it, which equals around 12.5 mpg, which is what I always get. The tires being larger will affect your speedometer and odometer - so your "miles per tank" is not right.

 

yeah agreeing with the tire size difference. if you haven't gotten it recalibrated (superchips, hypertech things, or go to the dealer) get that done. this will account for the decrease in mpg.

this is true only if it hasn't already been done or you put the bigger tires on without doing it. plenum, airfilter are also things to look at. i know my truck likes to lose acceleration or need higher rpms to get up to speed when my airfilter is clogged up. change that and man it's a new truck. sorta. doesn't sound like anything really is going wrong but another thing to keep an eye on is the catalytic converter. it could be getting plugged up. usually though it goes all at once.

check the tire size adjustment first. see if that helps.

 

hey..thanks for responding everyone.
ramdamit-i have not checked the plenum gasket.ill do some research on how to do this.i used to know but have long since forgotten.i recall it was a pain to change correct?
racin-my truck has the 26 gal tank as standard equipment. i have an options sheet from the dealer when i got it.it states that code YG7A is two extra gallons.NFWS being the 26 gal tank.this just led me to believe that it was a 28 gal.im guessin that its probably a larger filler tube?
crazy-when i got the truck it already had 285's on it.they were shot so i got new of the same size.its a good bet that the original owners did not get it recalibrated.should i take it to the dealer or get a chip.is there one that everyone likes and what would be more expensive?dealer or chip?
perhaps ill take a look at the k&n...clean it up good.
thanks again....

 

i get exactly the same amount of miles in my 01 318.. i had 285's getting around 320 a tank.. and yeah we have 26 gallon tanks and you dont run it empty so really your getting 320 to about 22-24 gallons... so you should be averaging around 13-14 mpg..

 

check your o2's

 

I was just about to also suggest o2 sensors but tim beat me to it.

 

i win

 

you can yank the front o2's out and clean them with CRC electronic parts cleaner. may help, spray them in the holes and dont be stingy. I've fixed/restored about 10 now all worked great afterwards.

to check your plenum, yank off the TB and look down into the intake with a mirror & flashlight. you should not see oil pooling on the bottom. a light film is normal, pooling is not.