caveman7815

since no one looks at the maintenance forum....ok so its a 2004 supercrew about 8 months ago added level kit fine A-ok....6 months ago add flowmaster 2.5 dual cat-back added at same time K & N 77 series intake...Gas mileage went up little say 16 around town 22 highway now i notice i am getting 10 around town and 16 if lucky highway.. This is on the digitial read out and i did the math mileage divide by gallons filled and it is a true reading ... so HELP GAS COST TO MUCH ...i did the intake and exhust for a boost now i am cutting my foot off....and driving hapits didn't change.

wde3477

Any fault codes - does the 'check engine' lamp come on? Does the engine sound or feel the same? BTW - which engine do you have?

It would seem that since you experienced improved mileage after the mods - they wouldn't be part of your current issue. Suggest you have another problem that has cropped up.

dewman

I have also noticed a drop im mpg in the last couple of weeks.
I think it might be the crappy "winter" gas...

dmille4.6

i just bought a 04 supercrew fx4 and have been doing a lot of research. several people have told me that the fuel filters clog up really easy. the previous owner of mine said he changed it every 10k.

wde3477

I know that the so-called winter gas has a lower octane to improve cold-weather starts and operability - but I suggest that something else is going on. Seeing a 30% or so decrease in mileage - only notice a 5-10% decrease on winter gas.

caveman7815

have a 5.4L ....i do notice a noise say going up a slight hill kinda get a chugging noise while steady on the gas kinda like hard to explain but it is normal throttle sound but its waves up and down. no check engine lights umm 36000 miles on it

Scot

Are you starting the vehicle to warm it up do to the cold? Having the convenience of remote start on mine and always preheating has killed my gas mileage via the display read out.

NGM

Do a full service on the truck. Change the oil, put in a 5w30 oil Change the spark plugs. Change the fuel filter. Service the transmission and rear diff. Make sure the filter is clean. It might be a lifetime filter but it has to be cleaned. Buy some MAF cleaner and clean the MAF. Do a BG induction service on the truck. I noticed my mileage dropping and I did this and it came right back. I did a Compression test to. Might want to do that make sure there is no internal engine problems.

JohnC

Put you truck on a dyno that can give you an accurate AF read out. From what I "hear" the K&N intake system will make the 5.4 run lean etc. and need to be installed with a tuner to make the corrections for increaded air intake. Not to mention you have an exhaust. I just think to be safe you should get the truck checked and replace the fuel filter as suggested. Good luck and keep us posted.

SuperDave

My mileage dropped similar to what yours did. I did what NGM did and had the same results as him, mileage went back to normal.