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  #1  
Old 10-18-2014, 11:35 PM
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Shitty MPG

i have a 2005 4.7l v8 and im getting like 12-13 highway mpg.. I feel like thats so shitty, anyone know what i can do to boost that up a bit? Note i also use 93 oct


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Old 10-19-2014, 07:14 PM
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Re: Shitty MPG

That is shitty. I'm having the same issues, but with the 5.7l. I just changed plugs & wires, pcv, & egr. I need to do the O2 sensors & the map sensor, and will do it this coming week. Also, make sure you're running the right engine oil. Not sure how much of a difference oil type makes in the 4.7l, but it affects a lot of things in the hemi.
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Old 10-19-2014, 07:44 PM
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Re: Shitty MPG

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Originally Posted by Furyous68 View Post
That is shitty. I'm having the same issues, but with the 5.7l. I just changed plugs & wires, pcv, & egr. I need to do the O2 sensors & the map sensor, and will do it this coming week. Also, make sure you're running the right engine oil. Not sure how much of a difference oil type makes in the 4.7l, but it affects a lot of things in the hemi.

I have no idea what to do i get literally 240miles to the tank thats shitty for me cuz i drive on the highway everyday..


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Old 10-19-2014, 08:43 PM
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Re: Shitty MPG

Well.. you're already ahead of me. Last full tank of gas has only taken me 185 miles & the "Low Fuel" message just came on... and the computer says I can go another 11 miles
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Old 10-19-2014, 08:57 PM
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Re: Shitty MPG

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Originally Posted by Furyous68 View Post
Well.. you're already ahead of me. Last full tank of gas has only taken me 185 miles & the "Low Fuel" message just came on... and the computer says I can go another 11 miles

That sucks also lmao **** man i need people to comment on here to help me


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Old 10-19-2014, 09:03 PM
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Re: Shitty MPG

They'll chime in. In the mean time... do a search on this site for "MPG's", "Gas Mileage", or "Fuel Efficiency". There are a lot of good threads on the subject.

Also, might want to give more info on your Jeep. Lifted? Tuned? Big tires? etc. All those things will affect mileage.
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Old 10-19-2014, 09:07 PM
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Re: Shitty MPG

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Originally Posted by Furyous68 View Post
They'll chime in. In the mean time... do a search on this site for "MPG's", "Gas Mileage", or "Fuel Efficiency". There are a lot of good threads on the subject.

Also, might want to give more info on your Jeep. Lifted? Tuned? Big tires? etc. All those things will affect mileage.

All stock except muffler upgrade for sound..


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Old 10-19-2014, 09:59 PM
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Re: Shitty MPG

When was the last time your plugs (and wires if applicable) were changed? PCV valve? MAP or MAF sensor (not sure which one yours has)? O2 sensors?

If you don't know... I'd start with those items. Not sure on yours, but my plugs need to be changed about every 35,000 miles. I just did them & the old ones looked like they were from the factory. Have you checked for any codes? A lot of sensor failures can affect your mileage too, which is why I asked about the MAP/ MAF & O2 sensors. 1 bad upstream O2 sensor can cause your car to run super rich.
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Old 10-19-2014, 10:17 PM
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Re: Shitty MPG

If the normal maintenance is ok ( air filter, plugs etc), i would put a scanner on it and check the O2 sensor voltages. The 1/1 and 2/1 sensors (both upstream from the cats) voltages should jump up and down between 0.2V and 0.8V. The more rapid they do this, the better. If this seems to be ok, then check the STFT figures (short term fuel trim). This figure is normally around +- 4 % (at a steady engine rpm) and as long as it stays in the single digit figures, its ok. You probably will see something like +20 or higher, what means that the PCM is adding fuel to the normal fuel schedule, increasing the fuel use and reducing the mpg.
If you donīt have a scanner with live data, an android phone with bluetooth dongle and the free "Torque" app can do the same for you.
You can also check the MAP sensor with the scanner. With engine off and ignition in run, the MAP figure should be close to the local atmospheric pressure. MAP is a very important input for the fuel injection and could be your problem as well.
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Old 10-29-2014, 08:15 PM
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Re: Shitty MPG

Man, both the 4.7 and 5.7 mpg is terrible. Last Saturday I got back from an almost 1800 mile trip in my mildly modified (see signature) 5.7 Hemi, and for the first time I drove over 400 miles on one tank of gas...408 to be exact.....on 18.1 gallons. That was at altitudes between 5000-6000 ft. at speeds of 70-80 mph. On the highway, my "distance to empty" almost always shows between 440-480 miles. I've never seen the low fuel light as the wife won't let me run it that low. This time she wasn't paying attention and I am sure it was getting close.

You guys definitely need to do what Frank says. If you don't have a way to check the integrity of the O2 Sensors and have over 75-80K on your vehicle, I'd just bite the bullet and change them all. As Frank said, make sure all the other maintenance is current first. I had a lazy one at 65K and changed all of them.....about $120 for all four.
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  #11  
Old 10-29-2014, 10:18 PM
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Re: Shitty MPG

I've found the best price for the NTK O2 sensors (NGK brand) @ Rock Auto. Even with shipping, they are cheaper than Summit Racing, and any of the local (at least my local) parts shops.

Downstream (23159) is $25.79 & the upstream (23160) is $20.79. 3 day shipping is usually less than $10.
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Old 11-30-2014, 12:14 PM
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Re: Shitty MPG

I suggest use 5W20 engine oil if you dont already use that.
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