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Old 04-28-2013, 11:14 AM
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Very low milage??

Hey guys, this is my first Grand Cherokee, 3.7L 2007 model, it's an export from the US and I bought it here in my country at a local car showroom. I haven't driven other similar WK models but I'm pretty sure that 10.0 miles/gallon is pretty damn low! I've owned it now for about a month or two, and have driven some 400 miles since I got it. When I perform a DTC check with the 3 key turn method I get 2 errors, P0138 & P0158, which according to a Google search have something to do with the O2 sensors.

Could these errors be the cause to such a low milage? Isn't it supposed to be somewhere in the range of 16mpg? What are the things that cause such a low milage? I haven't taken it yet to JEEP to do a full checkup, I just had it checked with a mechanic before I purchased it who said it was in good condition.

Appreciate all the help!

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Old 04-28-2013, 11:53 AM
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Re: Very low milage??

yes, they will certainly cause low mpgs
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Old 04-30-2013, 12:10 AM
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Re: Very low milage??

bad tires - extra drag is bad.
wrong oil for jeep??
low amount of oxygen entering the engine??
clogged with carbon build up???
bad spark plugs???
bad filters???

I'm not really sure, I'm just thinking about jet engines for the most part.
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Old 05-07-2013, 08:45 AM
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Re: Very low milage??

bad o2 sensors will definitely cause poor fuel efficiency. it will also cause other more costly problems if not addressed. it's highly recommended to replace the sensors with NTK sensors. i see them on rockauto.com for $25.79. you will most likely be replacing all four of them. the nice thing about the 2007 3.7 is the o2 sensors are all the same style.
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Old 05-07-2013, 10:58 AM
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Re: Very low milage??

What everyone above said is all true, and the items the Patriot listed should definitely be checked before you go much further, as they can all affect fuel economy. Since you're getting codes relating to the O2 Sensors though, this is probably where you'll find most of your issues.

The codes you have listed indicate that both rear sensors (after the cats.) are indicating a problem. The rear sensors are used solely to determine the effectiveness of the catalytic converters. First, how many miles are on the vehicle? If it's more than ~75K, I'd just replace them all, and eliminate them from the mix. If not, I'd try to find someone that has the means to read voltages of all the sensors when driving down the street, and also indicate both short and long term fuel trim readings. This will give you a better idea of where the problem(s) lies. Without this info. you'll just be guessing, although the O2 Sensors would probably be my first choice too. You could also have a converter and/or a wiring (a short) problem though. Please keep us posted on your findings, and good luck on your "hunt".
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Old 05-07-2013, 11:25 AM
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Thanks guys for all your suggestions and help. The car has around 96,500 miles on it. I think I'm gonna go ahead with replacing all the O2 sensors with new NTK ones and as well put a new PCV valve and new spark plugs. I just recently learned, after pulling the data sheet from jeep, that the car was initially sold to AVIS Rent a Car for 3 years! The showroom I bought it from said it only had a previous owner in the states, which clearly is a lie now.. I'm guessing the Jeep was poorly maintained since it was a rental and explains the low milage. I'm hoping to bring it back to new tho by tuning it properly. I'll update you on the mpg once I tune these few things.
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Old 05-07-2013, 11:56 AM
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Re: Very low milage??

actually rental cars are maintained very well, they are just beat to hell by the renters
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Old 05-08-2013, 08:48 AM
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Re: Very low milage??

Quote:
Originally Posted by roryh86 View Post
Thanks guys for all your suggestions and help. The car has around 96,500 miles on it. I think I'm gonna go ahead with replacing all the O2 sensors with new NTK ones and as well put a new PCV valve and new spark plugs. I just recently learned, after pulling the data sheet from jeep, that the car was initially sold to AVIS Rent a Car for 3 years! The showroom I bought it from said it only had a previous owner in the states, which clearly is a lie now.. I'm guessing the Jeep was poorly maintained since it was a rental and explains the low milage. I'm hoping to bring it back to new tho by tuning it properly. I'll update you on the mpg once I tune these few things.
my jeep has 105,000 miles on it. found the receipts from the previous owner when i was going through the manual in the glove box. they maintained the jeep very well, and i'm consistently seeing 17.5 mpg running 50/50 highway. you'll probably get close after you give yours a good tune up.
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Old 05-12-2013, 07:44 AM
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Re: Very low milage??

Just ordered 4 NTK 23159 sensors, going ahead with the jeepgcomans and rejected rekonings advice of replacing them all since its past 75K miles, plus that I found them on eBay for $18 a piece (bargain). I changed the spark plugs the other day, they practically had no head on them, mechanic was surprised that the engine was still running.. I'm already up to 14MPG just by changing those. Ordering PCV valve parts too. Will update soon . THanks again.
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Old 05-12-2013, 08:21 AM
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Re: Very low milage??

10 mpg = unburnt fuel making its way out of the combustion chamber into the cats. you will also have bad, i.e., clogged catalytic converters if this has been going on for a while. Those are pretty expensive to replace.
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Old 05-12-2013, 08:33 AM
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Re: Very low milage??

Quote:
Originally Posted by roryh86 View Post
Thanks guys for all your suggestions and help. The car has around 96,500 miles on it. I think I'm gonna go ahead with replacing all the O2 sensors with new NTK ones and as well put a new PCV valve and new spark plugs. I just recently learned, after pulling the data sheet from jeep, that the car was initially sold to AVIS Rent a Car for 3 years! The showroom I bought it from said it only had a previous owner in the states, which clearly is a lie now.. I'm guessing the Jeep was poorly maintained since it was a rental and explains the low milage. I'm hoping to bring it back to new tho by tuning it properly. I'll update you on the mpg once I tune these few things.
Check your local laws, most places the dealer must disclose previous daily rental on the contract.
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Old 05-12-2013, 08:48 AM
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Quote:
Originally Posted by dmsfun View Post
10 mpg = unburnt fuel making its way out of the combustion chamber into the cats. you will also have bad, i.e., clogged catalytic converters if this has been going on for a while. Those are pretty expensive to replace.
Wow thanks for the good news haha. How would I check/know if I have bad catalytic converters?
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