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Getting a big drop in gas mileage, why?
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New User
Joined: May 2012
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Getting a big drop in gas mileage, why?
Drive a 2004 Ford F150 4.6L V8 EXT CAB. It has 71,000 miles on it. Truck runs great, doesn't stall or miss and idles good but my gas mileage lately has been very bad. Oil, air filter and fuel filter have been changed. What could cause this?
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New User
Joined: May 2012
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Gauges seem to be working correctly and I have a anti-theft locking gas cap. A 100 mile or more loss of gas mileage to one tank of gas every time is big. As mentioned before the truck runs great, sounds great and doesn't stall or miss.
Posting Guru
Joined: Nov 2009
Posts: 2,016
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From: NC
Some great maintenance advice has already been given.
I'm just spit balling here. Have you recently changed gas stations? Higher ethanol content?
I'm just spit balling here. Have you recently changed gas stations? Higher ethanol content?
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Fleet Owner
Joined: Mar 2012
Posts: 26,155
Likes: 4,149
From: Near Cal. Avenue
Sounds like you are burning E85 now. Seriously though, that big a drop, look at clogged pcv hose or valve, change air filter, maybe something is in the intake side of the filter partially clogging it. Put a code reader on it and if you can freeze frame and graph the PID's in real running time, those would be great for us to know. Tune up time for sure.Using good synthetic oil make a big difference. Raising the Ethanol % in the gas is possible in some of the states or Big Cities. Is the motor reaching and staying at normal warm up operating temps? If thermostat is stuck open the fuel system will stay in rich mode. Sensor could also do that. Partially clogged exhaust will suck the fuel down. But motor might not show it unless you ask it for good power, than it may seem rather weak and slow to Rev. Scanner willshow if fuel system constantly switches from closed loup to open loup cycles.
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Super Moderator
Joined: May 2004
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From: Central Coast of CA
Per Chandler's suggestion, here is a how-to: https://www.ford-trucks.com/forums/8...l#post11456017
Stewart
Stewart
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Thanks for all the helpful advice...........also no check engine light has been coming on at all. It could be the gas around this area that I live in (Central Louisiana). I talk to a guy at autozone that said he and some other people were having the same problem.
Tuned
Joined: Mar 2003
Posts: 498
Likes: 18
From: Santa Fe
I'm getting around 350 miles per tank on average. It's about 16-17 mpg when I fill up with 19-20 gallons. 480 miles per tank, i would be ecstatic if im able to get that. Unless you got the 35 gallon tank option. I have the standard 25 gallon tank. I'm not sure if the bigger tank is offered on early model as 04.
Postmaster
Joined: Jul 2008
Posts: 2,565
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A lot of things can cause that much of a loss in fuel mileage. Higher ethanol content in the gas, transmission or torque converter lockup issues, tune up, leaky injectors just to name a few things. Losing 100 or miles per tank is drastic, so I would think it's more than just tire pressure. E-85 or injector leakage, or tranny issues would seem more of a culprit. Could also be cam timing issues. Just a few suggestions on where to look. You might even try gasoline that you know is all gasoline without any ethanol to see if that helps.
New User
Joined: Sep 2013
Posts: 4
Likes: 2
From: Annapolis, MD
Try taking a look at your thermostat. Get a scanner, start your truck and open the hood. Hold your hand on the upper coolant hose (the big black one above the alternator. Watch the coolant temp as the truck warms up. The hose should not get hot until the coolant temp reaches 190-195 degrees (that is when the thermostat opens up). Mine was stuck open and the truck was constantly in "warm-up" mode i.e. it was running rich the whole time I was driving in an attempt to get the truck to proper operating temperature. My gas mileage was about 10-11 mpg on the highway, and I had some serious lags in acceleration as well as a rougher idle. Swapped the thermostat ($15 part) and the problem was fixed. MPGs are back, power is back, idle is smooth. Just my $0.02.
