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Gas milage; 1998 Grand Cherokee limited.

Old 02-07-2019, 07:27 PM
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Year: 1998
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Default Gas milage; 1998 Grand Cherokee limited.

I am looking to improve my milage on my 98 grand Cherokee limited. I drive 27.5 to work daily (then another 27.5 home). On a 17 gallon tank, I get 200 miles.

​​​I don't take it off road. I can't get the cruise control to work, which would improve things if it did work since most of my commute is out of town. Keep the tachometer under 2k except when climbing bills.

I keep the fluids in good condition, just changed the transmission fluid last fall, and rebuilt the braking system aside from lines and master cylinder last month. I keep the vehicle light, just a spare, jack, and basic tools. The engine runs great, doesn't run rich or lean. I baby the thing.

Any tips other than what I have done already to improve my mileage. Some have suggested adjusting the fuel/gas mix to make the engine run more efficiently.
​​​​​​
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Old 02-08-2019, 01:54 AM
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I this a AWD version? I never understood the Quadra Trac. If I want my Jeep in 4 wheel drive I will put it in 4 wheel drive.
When is the last time you checked or replaced the plugs?
A clogged cat won't help.
O2 sensors. While they might not be throwing any codes poking around on the internet will tell you they should be replaced anyway
somewhere at 100 to 150K.
And how accurate is your MPG estimate?
Are you running bigger tires?
Cause that could throw off your calculations.
Also since it is winter I am wondering if you get the same mileage in the summer.
People talk about getting worse gas mileage from "Winter Gas".
I think it is just cause we let are vehicles warm up more but........
Also I am guessing you have an overhead console.
What does that say as far as average MPG goes.
I put one in my '00 XJ, did not come with one, and on longer trips the overhead console reading seems
to be fairly accurate. What is not accurate, least I am pretty sure, is my Miles Till Empty read out.
Also my gas gauge in the cluster is a little off. Almost positive.
When I fill up, and I fill up all the way when I do, she never takes quite as much gas as I think it will
from the reading on the gas gauge. About 2 gallons less then I think it will every time.

Sorry for the babbling. Just all the things that popped into my head when I read your post.
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Old 02-08-2019, 04:16 AM
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That's... quite low.
In addition to what Ralph77 said, I would strongly recommend the 4 port injector upgrade. I use Bosch 0280155703 in mine and they are a great improvement over the stock ones. Obviously part of that is the stock ones being 23 years old, but I believe there would be a not insignificant difference between them both brand new.
Check cylinder compression maybe.
Tire pressure good?
Also, are you measuring mpg with the console, or by gas fill ups + odometer readings? The latter is much more accurate and dependable, just make sure your tires are correctly sized to get proper odometer readings.
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Old 02-08-2019, 04:27 AM
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Originally Posted by Hatsuwr View Post
That's... quite low.
In addition to what Ralph77 said, I would strongly recommend the 4 port injector upgrade. I use Bosch 0280155703 in mine and they are a great improvement over the stock ones. Obviously part of that is the stock ones being 23 years old, but I believe there would be a not insignificant difference between them both brand new.
Check cylinder compression maybe.
Tire pressure good?
Also, are you measuring mpg with the console, or by gas fill ups + odometer readings? The latter is much more accurate and dependable, just make sure your tires are correctly sized to get proper odometer readings.
All good ideas. I also did the 4 hole injector upgrade. Did it help? I don't really know as far as MPG goes.
Butt dyno tells me she seemed peppier and idled a little more smoothly but just as Hatsuwr pointed out could
just be the fact that I replaced 15 year old injectors with a 145K on them. LOL.
All in all don't regret it one bit.
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Old 02-08-2019, 11:52 AM
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Have you checked your brakes are not dragging including the parking/hand brake ?
200 miles to 17 gallons is poor - especially if you are mostly out of town.
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Old 02-08-2019, 01:10 PM
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I get the same mileage as you to a tank and itís mechanically sound . Iíve driven countless 4.0ís never had one that got even half decent mpg and knew that going into it . The only place i see unbelievable mpg is on forums lol
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Old 02-08-2019, 02:34 PM
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Originally Posted by GreaseMonkey17 View Post
I get the same mileage as you to a tank and itís mechanically sound . Iíve driven countless 4.0ís never had one that got even half decent mpg and knew that going into it . The only place i see unbelievable mpg is on forums lol
Most of my journeys are under 5 miles into town and back again and I get around 12-13 mpg.
If I reset the MPG on the computer and make a longer journey of 10 miles+ I will get an average of closer to 18 mpg.
On a journey of 50+ miles on a good road with free moving traffic I've had 23 mpg average.
Jeep is a 2000 WJ 4.0 and has done under 82k miles.
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Old 02-09-2019, 12:18 AM
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Originally Posted by thatguy1 View Post
I can't get the cruise control to work, which would improve things if it did work since most of my commute is out of town.
​​​​​​
I assume that this is on a 4.0, check your vacuum lines as the cruise control is vacuum actuated so are the interior vents. if you're only getting defrost you definitely have a vacuum issue, I'd start at the "T" close to the fire wall on the passenger side and move from there. Also if your tiers aren't too oversized make sure that you have the pressures to what the sticker on the drivers door jam says, not what the side wall says, I believe its 36psi or so, too high and you can get a death wobble, too low and you kill gas milage. Ive always wanted to try it but never had the funds to buy six of them, I'm told that the 4 hole injectors from a dodge neon are a direct plug and play upgrade over sock in both power and economy. I'd also check spark plugs, I like autolite iridium xp's, in my opinion copper plugs aren't worth your time, just make sure they are not damaged and are properly gaped, a quick google tells me that if you have a distributor they should be at 35 thousandths of an inch and 40 if you have a coil pack (don't quote me, check your owners manual, and I think the sticker on the upper rad support also says it too)
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Old 02-09-2019, 03:03 PM
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Originally Posted by Cherokee_Mike View Post
Most of my journeys are under 5 miles into town and back again and I get around 12-13 mpg.
If I reset the MPG on the computer and make a longer journey of 10 miles+ I will get an average of closer to 18 mpg.
On a journey of 50+ miles on a good road with free moving traffic I've had 23 mpg average.
Jeep is a 2000 WJ 4.0 and has done under 82k miles.
from your post it sounds like youíre referencing the over head console mpg rather than true calculations . Next time you hit low fuel light fill it completely up and once it clicks off donít add more rest trip odometer and run til light comes back on fill tank until pump clicks off again and divide mileage it took to refill by miles driven this is the only truly accurate way to calculate it . Because this is the internet someone will chime in with an even more accurate way lol and thatís ok
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