FAQ - My gas mileage sucks - Page 6 - JeepForum.com
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post #76 of 108 Old 02-11-2014, 12:52 PM
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1998 XJ Cherokee 
Join Date: Feb 2014
Location: Montreal
Posts: 3
Gas milage


hello my jeep is killing me with gas consumtion 260 kn per tank... new 02 sensor and injector rail was liking...till same problem.. but when i touch the injectors, rail.. etc... then i got 350 km... Please help!

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post #77 of 108 Old 03-11-2014, 11:20 PM
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2004 WJ 
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Location: pittsburgh
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My mostly stock fipk 4.7ho gets 13-14 mixed and 18-19 hwy. I run 91-93 octane. I installed plastic to block the about 3/4 the rad on this and my truck in the winter. The quicker it gets there and the warmer the engine runs, the better the mpg.
My old 94zj 5.2 got 1-2 mpg higher mpg after I did a electric ford super coupe fan mod. Much faster warm up and less stress on the waterpump.
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post #78 of 108 Old 10-22-2014, 09:51 AM
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2008 JK Wrangler 
Join Date: Oct 2014
Location: fort myers
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very poor gas mileage

I have a 2008 wrangler , 3.8 , manual transmission with only 30,000 miles . I am getting approx 12 miles/ gal. engine light is on so the dealer ran a diagnostic to detemine issue. they told me i needed front and back 02 sensors replaced , which i did. 30 miles later engine light is back on and no improvement in gas mileage.
any suggestions ?
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post #79 of 108 Old 11-21-2014, 07:26 PM
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Help just dropped from 12.0 to 9.3 Jeep Grand Cherokee 5.7
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post #80 of 108 Old 11-21-2014, 07:29 PM
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I am only getting 9.3 it dropped today from 12.0 to 9.3 any ideas never been below 10.0 2010 Jeep Grand Cherokee 5.7 liter
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post #81 of 108 Old 02-24-2015, 04:27 PM
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1999 XJ Cherokee 
Join Date: Mar 2013
Posts: 6,044
Synthetic oils are less affected by temperature. So in cold weather that helps gas mileage some.
There's several things that I've done that improved my 4L gas mileage year round, city and highway.

The main items are 205F Stant thermostat, Kolak ignition kit with plugs at 0.045 gap, modern 4 injectors, high flow intake, 2.25" cat back, appropriate weight synthetic oils in everything, slightly positive rake, no winch or roof rack, and a few other things.

In cold weather a partial grill cover would also help, but I don't have one yet.

I made a thread about it. My 99 XJ currently gets 25 mpg at 60 mph (in coastal air) even with 30" tires, low lift, and 200 lbs skidplates.
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post #82 of 108 Old 02-24-2015, 04:44 PM
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1999 XJ Cherokee 
Join Date: Mar 2013
Posts: 6,044
P. S. - The Kolak ignition and my 0.045 gap is giving a longer and hotter spark.

The 205F thermostat helps engine get to at least 205F no matter how cold the weather, and if weather is above 25F my Jeep runs 210F (perfect).

The modern 4 hole injectors spray a fine mist of fuel instead of a single stream.

So from those things my combustion is hotter and more complete. So more efficient. I also have easier cold starts, runs smoother, and more torque and power.

I do not have any predetonation problems. I use 89 octane gas, though it might not be necessary. It runs smoother on 89, has slightly more performance, and I suspect 89 helps my gas mileage.
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post #83 of 108 Old 03-12-2015, 12:56 AM
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1999 XJ Cherokee 
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Here is a thread that lists affordable, cost effective mods that have improved my 99 XJ's 4L gas mileage.

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post #84 of 108 Old 03-17-2015, 01:46 AM
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My Engine light is on & some other stuff Please Help... Just bought my first Jeep, 2004 Liberty and I love it but the next day the engine light comes on, I take it back tell them what happened he plugs a machine in clears it and says sometimes when they fix something the computer doesn't recognize it right way but also my windows were flogging up the defrost wouldn't work, and when I rode over a speed bump my oil light came on and then went off. I went back again because I just paid everything I had for some reliable transportation and I need some answers they say it's a heater coil and to bring it back tomorrow on Tuesday and they will fix it. But, I want to be safe than sorry so if anyone can... please help me I plan on stopping by Auto Zone before I take it back and let them plug in their machine so I'll know for myself and get codes on my own. Please help. I know nothing about Jeeps but I love mine.
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post #85 of 108 Old 07-21-2015, 10:57 AM
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2008 JK Wrangler 
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Location: Oklahoma City
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I have a 2008 Unlimited with 3.8 L. I was averaging 14 mpg. I put headers on to replace stock manifolds....14.3 mpg. I added a spectra cold air intake......14.5-14.6 mpg. Then added Banks Monster cat back exhaust......13.0 mpg on highway.....13.6 in the city. At constantly down shifts and up shifts on highway at speeds 55 and up. I've changed plugs n wires and have used injector cleaner. Just seems like there's no top end on highway. Don't know if there's to much back pressure or not enough. Have heard I need to get computer related to all the mods. Any thoughts???
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post #86 of 108 Old 07-25-2015, 02:42 PM
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Two items not mentioned up to this point that greatly effect winter MPG are 1) cold dense air puts a much higher aerodynamic load on your jeep than summer air (so yes remove top carriers etc. if you can) and #2) gasoline is a blend of nearly 100 compounds (mostly 20-30 of them make up the bulk) and in the winter oil companies can and do use lower energy content light ends to make the crapoline cheaper but also to do a necessary thing- raise vapor pressure and lower boiling point for easier cold starts. In this case the lower energy content will mean poorer MPG than with summer grades of gas. There is nothing cost effective you can do about the second issue. There have been many good suggestions made about ways to improve MPG (and some not so good) so I will not expand on what was already stated.
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post #87 of 108 Old 09-01-2015, 01:06 PM
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the stock air box is designed to get Positive air to throttle it gives better response and fuel mileage and more torque at low rpm when cruising also it is colder air not hot expanded air from under hood. low restriction air systems are good for HIGH rpm and racing!
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post #88 of 108 Old 09-20-2015, 10:19 AM
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I've actually been told running a mid grade fuel for a jeep WJ will boost you from 400 km per tank to over 600.
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post #89 of 108 Old 09-21-2015, 11:32 AM
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cherokee 1350

Originally Posted by 91Cherokee7 View Post
I was getting around 13mpg until i started using (Lucas upper cylinder lubricant its like a 24oz bottle, 3oz per 11gallons of gas) which increased my mpg to 17-19. A total of around 50 more miles on a full tank.The stuff works people and its only $11 at walmart, Autozone.
this is about sealing top ring and lowering friction I use synthetic oil apx 3 oz every 5000 mi it is very noticeable!!!
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post #90 of 108 Old 10-10-2015, 05:09 PM
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1998 TJ Wrangler 
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Location: Silver City
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My son-in-law went to oversized mud claw tires from Big O. He also has 4.10 or so differentials. His mileage is unbelievably bad. About 9 around town, and I took it to Las Cruces from Silver City (NM) and got 10 on the way there with a lightweight empty trailer, and 7 on the way back with a refrigerator on the trailer. My 1989 Ford F-150 4X4 does about twice that. I would have gotten around 18-20 mpg each way, even with the trailer, a V8, and all that extra weight. Shameful.
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faq , gas mileage , improve mpg , miles per gallon , mpg , poor gas mileage

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