Sudden decrease in gas mileage; Help
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New User
Joined: Oct 2007
Posts: 14
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Sudden decrease in gas mileage; Help
Hi, yall. i have been a member for a while now but rarely post due to the great wealth of info. already on here. Wll here is my problem. i have a 1995 f250 with the 5.8 in it. About a month or so ago my gas mileage decreased dramatically. I went from 14-15 mpg, to 8.5 mpg. i have ran 4 full tanks and each time it has came out to 8.5 mpg. i have not done anything to the truck at all. It still drives the same and idles fine. I looked under the hood and just did a visual check to see if there was any burnt wires, or loose vaccuum lines, but that was not the case. If anybody could offer up any suggestions on what to check out i would really appreciate it.
Thanks
Steve
Thanks
Steve
Elder User
Joined: Jun 2007
Posts: 759
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From: Humble,Tx
Steve I could be wrong but I'd look into whether or not the 02 sensor is doing it's job or not. I'm more familiar with speed density as apposed to mass air flow efi but that would be one thing to consider
Lead Driver
Joined: Feb 2003
Posts: 8,140
Likes: 4
From: Oak Harbor, OH
Pull the codes. Something isn't right and the computer will tell what it is. OR at least help you get pointed int he right direction. This almost sounds like the fuel pressure regulator has failed and it's running full rich all the time. You're sure it's running any differently? Did you do any work no matter how minor to it? Plugs, wires, cap, rotor all in good shape? They are the cheap autozone parts are they? Motorcraft copper plugs, Napa gold line or whatever it is now for the cap, rotor and wires this will cost about ~$150 for all of it. You don't want to skimp on the ignition system. You wouldn't want your doctor to use "cheap" connecting parts on your pacemaker would you? The ignition is the heart of the truck. No fire, no go. It may very well be running rough but you don't notice it because you drive all the time. It slowly gets worse until you do, but even now you're noticing the effects. It's also that magic time of year when the gas formulas change for winter. I lost 3 mpg in my intrigue from the fuel switchover. But it needs a tune up too.. So I might be able to reclaim some of that.
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 13
From: Sand Lake, MI
When my 5.8 fuel mileage drops like that, down to around 8 from the norm of 13-14 first thing I do is run the KOER test, so far every time I've got that dreaded 172 code.
Replace the O2 sensor and back to normal again, milage back up.
No more "napa" 02 sensors for it. Can't seem to get much more then 10 months or so out of em from them for some reason with it.
Replace the O2 sensor and back to normal again, milage back up.
No more "napa" 02 sensors for it. Can't seem to get much more then 10 months or so out of em from them for some reason with it.
