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Low MPG in a 3.7 KJ
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Author:  Jay4 [ Sat Mar 24, 2012 9:47 am ]
Post subject:  Low MPG in a 3.7 KJ

Afternoon Gents

Please would you assist.

My 2003 KJ has 96000mi on the clock, she is currently giving me 11.7MPG, this is a mixture of town and highway driving, she seldom sees more than 2000rpm so i have a very light foot. I am sending her in for a major service next week, i recently purchassed the Jeep and dont think the the plugs have been changed in ages. The Cats are all fine.

What else can i look at to sort my MPG out...ive read that the MAP sensor can play a part in high MPG,if so please would you assist me in locating and cleaning this out............. please assist!

Thanks
Jayson
South Africa

Author:  L.O. [ Wed May 02, 2012 7:58 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

Wow...that is some poor mileage. Sure, new plugs will help and check air filter and really anything else replaceable in the anti-pollution system. Some KJs have mileage issues. Check out some other threads on this site concerning mileage. Good luck!

FYI: I am getting 21.5 mpg mixed city and highway

Author:  tjkj2002 [ Wed May 02, 2012 8:24 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

Jay4 wrote:
Afternoon Gents

Please would you assist.

My 2003 KJ has 96000mi on the clock, she is currently giving me 11.7MPG, this is a mixture of town and highway driving, she seldom sees more than 2000rpm so i have a very light foot. I am sending her in for a major service next week, i recently purchassed the Jeep and dont think the the plugs have been changed in ages. The Cats are all fine.

What else can i look at to sort my MPG out...ive read that the MAP sensor can play a part in high MPG,if so please would you assist me in locating and cleaning this out............. please assist!

Thanks
Jayson
South Africa

Believe it or not but in bold is the #1 cause of bad mpg's.Promotes massive carbon buildup in the intake which drastically reduce mpg's.Gotta get out and "clean the cobwebs out" at least once a week,IE drive like you stole it for at least 30-60mins once a week,does wonders.

Author:  Jay4 [ Thu May 03, 2012 3:04 am ]
Post subject:  Re: Low MPG in a 3.7 KJ

Wow, I cant believe that, will def give it a go, many thanks!

Author:  5characters [ Wed Nov 28, 2012 2:36 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

True story, alot of times you just need to get up on it, when i was in the Force we had F-350s that we would drive around the line, (never over 15 mph) and once a month we had to take them to the highway and drive them like a normal truck, not entirely what you were talking about but I actually had something to add to the conversation so I took my shot.

Author:  JeepCoMj [ Sat Feb 23, 2013 12:06 am ]
Post subject:  Re: Low MPG in a 3.7 KJ

In fact, alot of the issues with liberties dropping valve seats or having valves fail is due to the fact that Chrysler didn't design the valves to rotate as well as they should (which keeps the seat clean and the seal good, as well as keeping the valves appropriately lubed)

My xj gets 24-25mpg all day IF i stay in the "sweat spot". this is where the HP and Torque curve meet, right around 2250rpm on stock, but mine meets around 1850RPM with a torquer cam.

My KJ gets around 19mpg with 4.10 gears and 32" Hankook MT's, with mixed driving, hitting 2750RPM as much as possible.

Keep it lower, it gets worse.

Author:  stev0 [ Sun Mar 17, 2013 2:43 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

11mpg! :shock: I do almost 19 granny'in around. I dont see much difference cruising at 60mph or 75mph on the open road. Then again, I am bone stock.

Author:  tjkj2002 [ Sun Mar 17, 2013 7:27 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

stev0 wrote:
11mpg! :shock: I do almost 19 granny'in around. I dont see much difference cruising at 60mph or 75mph on the open road. Then again, I am bone stock.

I get 9mpg's city,but yeah far from stock.

Author:  djr8505 [ Mon Mar 18, 2013 9:02 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

I noticed that traveling around 75 I would average around 16.7 mpg (evic readout). If I was going 65 I got 19.4. Mine has a 5 speed though (stock for now).

Author:  djr8505 [ Mon Mar 18, 2013 9:02 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

I noticed that traveling around 75 I would average around 16.7 mpg (evic readout). If I was going 65 I got 19.4. Mine has a 5 speed though (stock for now).

Author:  TheJawsOfDeath [ Sun Jul 07, 2013 6:19 am ]
Post subject:  Re: Low MPG in a 3.7 KJ

I've noticed that no matter what speed or engine rpm I maintain, my liberty is a gas hog. That's why I have an old honda civic with the smallest engine. Gotta love over 40mpg with no hybrid nonsense just small light cheap and stingy.

Author:  kj-dec [ Mon Oct 14, 2013 12:39 am ]
Post subject:  Re: Low MPG in a 3.7 KJ

I'm in ill annoy and in an attainment area so stuck with some of the most wretched ethanol diluted chemically contaminated EPA violated fuel in the country. My 2002 Limited (tall version before they lowered them) has never gotten better than 12MPG city. It used to get about 21 highway once we got out of the area and could get real gasoline. I do mostly city driving, not grannnying, but get out on the freeway at least every other week.

Over the years I've done plug replacement, K&N filter element, AMSoil filter element, exclusive use of Mobil-1 oil, cold air induction, Sea Foam treatment, 2.5" cat-back exhaust, various tire pressure variations, and replaced the tires. I've also pulled the back seat out (just flat storage back there now, and its generally empty). Nothing made city mileage go over 12MPG except getting real unadulterated gasoline (in which case I currently get 13.5 or so). Last highway trip was 18.5MPG but the states we drive through no longer have readily available non-ethanol gasoline.

At this point I've given up on trying to improve it. Just going to keep driving it until its time for a new vehicle.

Author:  jeepsterkj [ Fri Jul 20, 2018 5:41 pm ]
Post subject:  Re: Low MPG in a 3.7 KJ

If you want better MPG you need to ditch the 3.7 gas guzzler and get a 2.8 CRD instead, preferably one with a manual six speed gear box, like mine...I average 38mpg in mixed driving, dropping to around 33mpg with the Aircon on all the time. :wink:
PS, and mine is a 4x4!

Author:  mercdude [ Fri May 24, 2019 3:10 pm ]
Post subject:  Low MPG in a 3.7 KJ

Change the o2 sensors front and rear both banks and make sure cats aren’t plugged. A muffler swap and piggyback tuner will add a few mpg. Stock height with 02 limited 4wd, I’m getting around 24 hwy at best worst 20 hwy. avg about 20, which I consider good

I would have gotten a crd but they were double the cost and half as nice as my 02... the crds don’t get THAT much better mpg.

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