Why is my fuel mileage less than 8 mpg???

[mountaineerbeast]

Since my last fillup at a shell with my 97 Mountaineer i have gone about 80 miles on a half a tank of fuel (that's 10 gallons). I will add that i normaly get about 13 or so, but more recently around 10 mpg city and off road driving. With this last fill up i have gone about 30 miles through 10 inches of snow at about 35-45 mph. I also did some AWD snow drifting and some mudding.

It also seems like the fuel mileage has been getting worse and worse over the short course of this single tank of gas. It seems like i may be even getting around 6.7 mpg?

Could this be a sign that my engine may not live much longer?
Or could my fuel management system be going crazy?

Or is it the cherry bomb vortex and k & n filter (with stock air box) that has ruined my fuel economy in combination with the altitude of 4600 feet?

 

[yavapaires]

CI experienced a similar problem last week. It snowed nearly all day, so, anxious to try the brown wire mod, I did quite a bit of playing in the snow. My 96 4.0 OHV needs a new thermostat, so it was running too cold for the computer to do it's thing. So I got only about 45-50 miles before the fuel gauge dropped to the full mark. Normally I get nearly 100 miles. Coming home that night, the temp barely showed off the cold mark, and the CEL came on. Checked the code, bad O2 reading. Cleared the code, been fine ever since,gas mileage appears to have gotten back to normal (app 20 mpg). I also have not been using StarTron in the last couple fill ups, trying to see if the altitude and different gas will make a difference. So, long story short, playing in the snow will use more gas, especially if engine is running cold.

 

[ahodges]

Since my last fillup at a shell with my 97 Mountaineer i have gone about 80 miles on a half a tank of fuel (that's 10 gallons). I will add that i normaly get about 13 or so, but more recently around 10 mpg city and off road driving. With this last fill up i have gone about 30 miles through 10 inches of snow at about 35-45 mph. I also did some AWD snow drifting and some mudding.

It also seems like the fuel mileage has been getting worse and worse over the short course of this single tank of gas. It seems like i may be even getting around 6.7 mpg?

Could this be a sign that my engine may not live much longer?
Or could my fuel management system be going crazy?

Or is it the cherry bomb vortex and k & n filter (with stock air box) that has ruined my fuel economy in combination with the altitude of 4600 feet?

Is the CEL on? sounds like bad O2 sensors or a heavy foot.

 

[corkey]

don't recommend trying the brown wire mod on a Mountaineer,

it's probably a v8 with AWD anyways,, i would say check your iac, and throttle body and MAF sensor, maybe clean them all, than unhook the battery for an hour or so, than go for a slow comfortable drive, and see what that does,,

 

[mountaineerbeast]

Quick update:
Currently get about 15 mpg on the highway with my 5.0 v8.
And get about 9 around town.
Not hammering the throttle for a full tank barely helps.

 

[ahodges]

Quick update:
Currently get about 15 mpg on the highway with my 5.0 v8.
And get about 9 around town.
Not hammering the throttle for a full tank barely helps.

How do expect us to help if you don't answer any of our questions? I agree that is very low, but there are a dozen or more things that could be causing it

 

[swshawaii]

Ditto.

Is the CEL on? sounds like bad O2 sensors or a heavy foot.

How do expect us to help if you don't answer any of our questions? I agree that is very low, but there are a dozen or more things that could be causing it

 

[1996BLKBauer]

My Fuel mileage is bad because of 2 things so far that I have noticed...

1, I start my truck up in the winter to warm up
2, my o2 sensor is bad....

 

[fingers21]

If it just been this one tank, could it not be bad fuel? I wish it snowed enough here to have some fun, even if it meant i only get 8 mpg!

 

[gonenuke]

Are you just using the fuel gage to get these numbers, or are you calculating by how many miles you get between fill ups?

Start full record mileage
have fun
refill again record mileage

subtract refill miles from start miles and divide by number of gallons you get at refill.

 

[colintrax]

^do what he said. Anyways, snow and spinning the tires will hurt gas mileage. As will mudding.
If the truck is running fine and no cel, I'd say you're checking gas mileage wrong or you're paying the price for having fun

 

[jremington59]

That's normal for that vehicle. I have the same engine and I added a new cold air intake, catback exhaust and synthetic fluids and I can get 17 in the summer taking it easy on the throttle.

Quick update:
Currently get about 15 mpg on the highway with my 5.0 v8.
And get about 9 around town.
Not hammering the throttle for a full tank barely helps.

 

[gavin]

if you ended up getting some fuel with ethanol, while cheaper than pure gas, nets worse fuel milage.

I get about 9mpg city with 33's and 4.56 gears; 12mpg mixed city/hwy

 

[mountaineerbeast]

I'm not using the fuel gauge to calculate because it's rubbish.
I think my terrible fuel economy may have to due with my cherrybomb vortex and K and N air filter.
OR the gas stations are lying their ***** off and the fuel is really E-15 and not E-10 like it's supposed to be.
I do recall my truck running like absolute $%&* after filling up at an Exxon once. The sticker on the pump just said contains ethanol.

 

[swshawaii]

E10 (gasohol)
E10 (also called “gasohol”) is a blend of 10% ethanol and 90% gasoline sold in many parts of the country. All auto manufacturers approve the use of blends of 10% ethanol or less in their gasoline vehicles. However, vehicles will typically go 3–4% fewer miles per gallon on E10 than on straight gasoline.1

Negative 3-4% MPG is guaranteed to raise a few eyebrows. :thumbdwn:

www.fueleconomy.gov/feg/ethanol.shtml

 

[TexasEnforcer]

Fuel mileage 9 mpg

Hello, fellow explorer

my 1999 explorer gets 9 miles to a gallon. try fuel log for fuel logging its a great app. i changed everything on my vehicle and i still get the same mijeage. tank fills up with 32 gallons until i went into mexico and got a red light at their point of inspection. they sent me to a weight station. there we found out this explorer weighs 15976lbs than the normal weight of 4053. it looks like a normal explorer inside and out. just has a double tank. aluminum rims. Weird. Carfax says Executive Vehicle. i took it to my local police dept they verified that the vehicle is an Executive Transport Vehicle. and had been modified to withdstand being shot at.

 

[mrboyle]

Cold weather driving, letting the engine/vehicle warm up before you drive, heavy acceleration while playing in the mud and snow will all lower fuel mileage. You can not rely on one tank of fuel to determine if you are getting bad mileage especially if you combine all the activities you mentioned in your first post. Try keeping a record over three to four tanks of fuel to determine what the mileage is.

 

[koda2000]

in addition to the above mentioned suggestions...

is your temp gauge reading around the center of it's sweep? if it's on the cold side you ECU will not enter "closed loop mode" because the engine isn't reaching normal operating temp (usually due to a bad thermostat). that will have a negative effect on fuel economy. the same thing can occur if your temp sensor isn't telling the ECU the correct engine temp. another thing to consider is how many miles are on your upstream O2 sensors. if over 80-90k they may not be reporting the correct readings back to the ECU. this can cause the ECU to increase the injector pulse width, adversely effecting fuel economy. try running a finger inside the tip of your exhaust pipe. it should not come out black & sooty. these things usually turn on the CEL, but not always.

BTW, i don't see where your K&N air filter or muffler would have anything to do with your problem and your ECU should adjust for altitude.

 

[SoNic67]

I had the surprise of 8MPG recently.
I changed my fuel cap to a lockable one and now I have again the 15.5MPG (combined city/HW, mostly city).

 

[rb142]

That mileage is completely normal given the conditions inthe original post. It isn't clear that there IS anything wrong. The mileage needs to be checked over a longer period, and more normal conditions to determine whether it really is too low.