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Unread 03-26-2014, 09:06 PM   #1
morrie
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1999 XJ Cherokee 
 
Join Date: Feb 2012
Location: Birmingham, al
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Chasing 25 mpg

I am driving a stock '99 XJ Cherokee 4.0 Automatic transmission. After reading several posts from the thread entitled "My goal is to get 25+ MPG from my '99 XJ Cherokee" started by Charley3...I have joined his quest to achieve that same goal.

Thus far, I have done the following to help reach that 25MPG goal.
1) Autolite Plugs & wire set
2) Acell Distributor cap & Rotor
3) Bosch 4-hole Fuel Injectors
4) 2004 Fuel Rail
5) Monroe sensa-trac Shocks (all 4)
6) 205-F Stanton Thermostat
7) Removed Luggage Rails
8) BFG 235/70R/15 Tires

Considering adding a Dynamax Super Turbo Exhaust System & removing the Dent in the stock exhaust system located below headers which may give me another 1 mpg

Thus far I have run only one (1) tank of gasoline and achieved 17 MPG. up from 14 MPG. This is a combination of City/Highway. I started my second tank today. (3/26/14). I have yet to check only the Highway MPG. There is a trip to Panama City Beach, Fl. coming up in late April which will give me the opportunity to check the Highway MPG. I will update this thread for those of you who are interested.

Note* After replacing the Fuel Injectors, the throttle response is much better.

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Unread 03-26-2014, 09:15 PM   #2
tbburg
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Look around for a "high altitude"crank position sensor. It's a CPS that has the sensor mounted slightly forward of the standard position, and it gives you a degree or so of timing advance. It's supposed to net a little efficiency.

There's a thread over on NAXJA.org (link to NAXJA) on modifying a stock sensor to achieve the same result, but I don't remember if it was in the "mod tec" or the "street and performance" subforum.

Good luck with the "25mpg" 'Best I've ever gotten was 22.
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Unread 03-27-2014, 12:20 AM   #3
CoyoteHunter
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I love the sound of my Dynomax super turbo. Not overly vicious but a nice growl.
I've been wondering if switching over to E-fan would help you net more efficiency.
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Unread 03-27-2014, 01:01 AM   #4
Renix
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Here's how you do it. Sell it buy a Toyota. I've read tons of these treads and they crack me up. I wish you the best of luck. An xj is like a brick being thrown in the wind. Not very aerodynamic. Better gas mileage is all about efficiency in all areas and that boat anchor you drive is not gonna play nice.
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Unread 03-27-2014, 06:10 AM   #5
scupking
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I get a little over 15mpg stock all around town and no highway so I don't think you gained much at all. I think you will get more with a k&n filter, 62mm tb, high flow cat and the super turbo muffler. Also make sure you have new 02s, tps and iac.
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Unread 03-27-2014, 11:55 AM   #6
morrie
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Quote:
Originally Posted by CoyoteHunter View Post
I love the sound of my Dynomax super turbo. Not overly vicious but a nice growl.
I've been wondering if switching over to E-fan would help you net more efficiency.
Do a search on the E-fan. You will probably get different opinions on this subject. The thread by Charley3 has some good information you might check out.
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Unread 03-27-2014, 12:03 PM   #7
morrie
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Quote:
Originally Posted by scupking View Post
I get a little over 15mpg stock all around town and no highway so I don't think you gained much at all. I think you will get more with a k&n filter, 62mm tb, high flow cat and the super turbo muffler. Also make sure you have new 02s, tps and iac.
I might consider the K&N filter, but it would not give me any significant mpg increase if any at all. I do not have any issues with the O2 sensors, but since they are not too pricey, I would definitely consider replacing my old ones....probably never been replaced. After reading numerous posts about the Throttle Body...probably will leave it stock. I'll be getting the Dynamax exhaust system after April. Thanks for your input...appreciate it.
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Unread 03-27-2014, 12:09 PM   #8
morrie
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Quote:
Originally Posted by Renix View Post
Here's how you do it. Sell it buy a Toyota. I've read tons of these treads and they crack me up. I wish you the best of luck. An xj is like a brick being thrown in the wind. Not very aerodynamic. Better gas mileage is all about efficiency in all areas and that boat anchor you drive is not gonna play nice.
LOL....yea, man I know the XJ is a "boat" and there are not many aerodynamic mods (if any) that will make a difference. So, I will stay with the efficiency changes. As for the Toyota....I'll stick with my BMW Z3 Roadster... much more fun in the "ultimate driving machine".
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Unread 03-27-2014, 12:14 PM   #9
morrie
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Quote:
Originally Posted by tbburg View Post
Look around for a "high altitude"crank position sensor. It's a CPS that has the sensor mounted slightly forward of the standard position, and it gives you a degree or so of timing advance. It's supposed to net a little efficiency.

There's a thread over on NAXJA.org (link to NAXJA) on modifying a stock sensor to achieve the same result, but I don't remember if it was in the "mod tec" or the "street and performance" subforum.

Good luck with the "25mpg" 'Best I've ever gotten was 22.
Thanks for the info. I registered at the NAXJA today....appears to be an informative site. I'll dig deeper into the CPS ideal.
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Unread 03-27-2014, 12:18 PM   #10
morrie
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Quote:
Originally Posted by scupking View Post
I get a little over 15mpg stock all around town and no highway so I don't think you gained much at all. I think you will get more with a k&n filter, 62mm tb, high flow cat and the super turbo muffler. Also make sure you have new 02s, tps and iac.
What transmission is in your 99 XJ ?? I have noticed that a 4 speed trans gets better mileage than an automatic. If my trans ever goes, I'll probably consider replacing it with a 4 or 5 speed.....depending upon cost.
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Unread 03-27-2014, 12:23 PM   #11
WhammyXJ
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Quote:
Originally Posted by morrie View Post
LOL....yea, man I know the XJ is a "boat" and there are not many aerodynamic mods (if any) that will make a difference. So, I will stay with the efficiency changes. As for the Toyota....I'll stick with my BMW Z3 Roadster... much more fun in the "ultimate driving machine".
Agreed Morrie! My 330i is much more fun than a 'yota
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Unread 03-27-2014, 04:04 PM   #12
mschi772
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Quote:
Originally Posted by Renix View Post
Here's how you do it. Sell it buy a Toyota. I've read tons of these treads and they crack me up. I wish you the best of luck. An xj is like a brick being thrown in the wind. Not very aerodynamic. Better gas mileage is all about efficiency in all areas and that boat anchor you drive is not gonna play nice.
Piss-off with that stupid "haha, buy a different car" attitude. There's always one of you chiming into MPG discussions, and my patience for it is simply gone. I've outlined in great detail in the past multiple reasons why this is a legitimate pursuit, so I'm not about to repeat them all again.

I have to ask, though:

If your reasoning is that we shouldn't care about improving the MPG of the XJ because it gets crappy MPG compared to other cars. Well, please enlighten us. How much MPG must a vehicle get to make it a valid candidate for MPG improvement mods in your eyes?

If I can get 20 MPG out of an XJ instead of 15, no, 20 still isn't very great by modern standards, but that's 5 more MPG than before (a 33% improvement). That MATTERS especially to someone putting 10-15k miles on their XJ annually. Significant MPG improvements can be made very often for such little monetary investment that they pay for themselves in very little time. Everything I've ever done to my XJ to improve its MPG has already paid for itself and then some, and I've only owned the thing for less than three years. I've saved myself hundreds of dollars per year given how many miles I put on my XJ, and I've only raised its average MPG by about 3 or 4 so far.

Quote:
Originally Posted by morrie View Post
LOL....yea, man I know the XJ is a "boat" and there are not many aerodynamic mods (if any) that will make a difference. So, I will stay with the efficiency changes. As for the Toyota....I'll stick with my BMW Z3 Roadster... much more fun in the "ultimate driving machine".
There ARE aerodynamic mods you can do with varying levels of difficulty that will make a difference. I personally introduced many of them in Charley3's 25 MPG thread. They won' turn the XJ's drag coefficient from a 0.5 to a 0.3, but they will make a difference. A few guys on EcoModder.com have gotten mid-20's with only mildl to moderately modded XJ's (4x4 automatics).
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Unread 03-27-2014, 05:54 PM   #13
morrie
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Hey, 772...I have looked on Eco-modder.com and they have some interesting ideals. It might be something I would consider in the future. At present, I am concentrating on efficiency improvements/mods. I was excited to see my mph increase 3 mph (from14 to 17). It lets me know what I have done was not in vain. My main goal is to get the 25 mpg Highway miles. That would be an increase of 5mpg. I can live with that. Thanks for your vehement tongue lashing to those less uninspired to recognize the rewards of overcoming existing challenges and setting new goals for our vehicles.
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Unread 03-27-2014, 07:16 PM   #14
Renix
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Quote:
Originally Posted by mschi772 View Post
Piss-off with that stupid "haha, buy a different car" attitude. There's always one of you chiming into MPG discussions, and my patience for it is simply gone. I've outlined in great detail in the past multiple reasons why this is a legitimate pursuit, so I'm not about to repeat them all again.



I have to ask, though:

If your reasoning is that we shouldn't care about improving the MPG of the XJ because it gets crappy MPG compared to other cars. Well, please enlighten us. How much MPG must a vehicle get to make it a valid candidate for MPG improvement mods in your eyes?

If I can get 20 MPG out of an XJ instead of 15, no, 20 still isn't very great by modern standards, but that's 5 more MPG than before (a 33% improvement). That MATTERS especially to someone putting 10-15k miles on their XJ annually. Significant MPG improvements can be made very often for such little monetary investment that they pay for themselves in very little time. Everything I've ever done to my XJ to improve its MPG has already paid for itself and then some, and I've only owned the thing for less than three years. I've saved myself hundreds of dollars per year given how many miles I put on my XJ, and I've only raised its average MPG by about 3 or 4 so far.



There ARE aerodynamic mods you can do with varying levels of difficulty that will make a difference. I personally introduced many of them in Charley3's 25 MPG thread. They won' turn the XJ's drag coefficient from a 0.5 to a 0.3, but they will make a difference. A few guys on EcoModder.com have gotten mid-20's with only mildl to moderately modded XJ's (4x4 automatics).
And there is always one of you that cant take a joke, If you read carefully I said I wish you the best of luck. So if you have outlined in such great detail and know so much then you already know that the xj gets 20 hwy mph brand new off the lot ( I have in my hand the original dealer sticker if you would like a copy of it). Those MPG ratings are the best numbers they got from testing with a brand new motor at optimal efficiency. That's $2660 dollars a year at your 15k driving annually on a average $3.50 a gallon price tag. At 30 mpg that's $1750. So your looking at saving $900 a year. That's about one extra tank of gas a month. This is all assuming that you never do anything with your jeep except drive in a straight line and drive staring at your rpm gauge to keep your jeep in a optimal fuel saving mode. Then map out your route for the most downhill travel, turn it off at stop lights and coast as much as possible.

Buy the time your done spending money on parts i.e. exhaust, spark plugs, blah, blah, blah. You have gone backwards in pursuit of saving money. Because the L6 motor is working against you. Its heavy, the pistons are much larger than most creating friction and drag, and the straight design produces more vibration than a V6. The L6 was never designed for fuel efficiency, It was designed for low end torque and longevity. The L6 will never be as efficient as a V6 even if you dump thousands of dollars into it. So all of this means that your power to weight ratio and power transfer to the rear axle is going to suffer. Tack in the drag from the flying brick, (calm down its a joke) and your left with trying to pursue a task with something that it was never meant to do. Not saying you shouldn't try.

If you really want to go down this rabbit hole. The first thing you need to do before spending any money on engine and exhaust is...

Gut the interior leave one seat to drive with though. Find anything that adds weight to the vehicle that is not needed and remove it.

Lower the jeep and remove anything that creates drag on the outside, door handles, roof rack, fender flares........

Find a set of wheels that tucks the tires under the jeep without sticking out.

Find tires with the least rolling resistance.

Do not fill your gas tank up all the way, it adds weight.

And one of the most important things. Map out your daily drive. inclines, declines, stop lights, time of day left hand turns versus right yes it makes a difference. and your over all style of driving.

Or you could have bought a toyota, relax its ok to have fun.
Best of luck.....
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Unread 03-27-2014, 07:29 PM   #15
BlueRidgeMark
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Quote:
Originally Posted by morrie View Post

Thus far I have run only one (1) tank of gasoline and achieved 17 MPG. up from 14 MPG. This is a combination of City/Highway.


I don't want to rain on your parade, but both my '94 and my '97 get 18 regularly, and that's mixed highway (70 MPH) and stop-n-go commuting.


No special mods. Regular ethanol gas. Champion plugs. Standard stuff.


The '94 has 225/15 AT Grabbers and the '97 has 235/15 .... Doh! I forgot! Anyway, they are similar to the AT Grabbers. Meh. They were on it when I got it, and are close to being replaced. I'll probably drop them down to 225s. They rub once in a while on hard cornering.
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