• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

MPG increases?

Y

yossarian19

NAXJA Forum User
Location
Grass Valley, CA
Right. Jeeps get bad gas mileage. Admitted - I bought the wrong vehicle for cheap driving. That being said -
All conventional wisdom points at efficiency of ignition and free-flowing intake / exhaust.
For the 98 model year 4.0, I'm looking at:
MSD ignition
99+ Intake
Large filter / smoother intake plumbing
Re-routing the "suck" side of the filter to draw cold air
Better flowing exhaust / flowmaster 50 & hi-flow cat?

What else could be optimized on a 98? I'm looking for projects as much as results...
 
Driving style, do a basic tune up. Stock ignition is fine i don't think you'll see an improvement with the MSD. Headers back exhaust and high flow cat w/ bored throttle body and an intake w/ heat shield would be your best bet to increase it.
 
synthetic fluid in your diffs and transfercase
lose the roof rack / other accessories to create drag (windows up with no ac on)
electric fans
no front drive shaft
lose the gear in the trunk for weight savings


and my favorite :)
Drafting on the freeway
 
or buy a civic.
 
is it lifted, skidded out, rock sliders custom bumpers etc? Or is this a close to stock XJ.

Your dollars are better spent keeping high quality plugs and wires, new air filter like K&N which i think gives me a slight .75 mpg help, i also have borla header and new cat, and a flowmaster 50 series thourgh 2 1/2 pipes. I am happy with 16 mpg

What milage have you been getting and how long. Please track it over a long time not two tankfulls as it can really vary 20 % just weather, roads, and speed. You need to track for a few months to have any reliable data, clear out the trip odometer, fill the bad boy up, and write down milage to the fraction of a gallon when you fill up. Then average it out in 4 months or so.

I dont think spending much money beyond the tuner up stuff of highquality cap, rotor, wires, and air filter, and MAYBE o2 sensor. Anything else is not gonna get the greatest return on your dollars.

Check dino's web site on his homade cold air intake, take out the baffle in the intake tube. clean throttle body, run some sea foam in the oil. Try a gas treatment if you buy cheap crap gas.

You can spend 2 grand on fancy electronics, port and polish head, blah blah blah and still get 17 mpg.

Go buy a geo metro/ suzuki swift (which if you can find a swift GT is actually a cool car for what it is) or ford festiva for $1000 and get 56 mpg.
 
lancey3 said:
Driving style, do a basic tune up. Stock ignition is fine i don't think you'll see an improvement with the MSD. Headers back exhaust and high flow cat w/ bored throttle body and an intake w/ heat shield would be your best bet to increase it.
Click to expand...

X2. on the Stock iggy and MSD. I've actually seen MSD's do worse, and actually screw up the ignition on other vehicles. Guy I used to work with put one of those MSD's on his 98 Dakota to try and boost his mileage as he used the truck for delivering, and after putting the MSD on, it actually made it to where every time he shut the truck off, it will still try to continue and fire....meaning it wouldn't just shut off, it would gradually stumble and eventually shut down.

Invest in good tune up equip, keep it tuned up on a regular basis, take it easy on the go pedal, and don't run the absolute most cheapest gas you can find. Doing this has yielded me an average of 17-18 around town, and 19-20ish highway depending on what town, and what highway.
 
j33pownr said:
and my favorite :)
Drafting on the freeway
Click to expand...

I will continue to do so untill I get a ticket for drafting. Haven't gotten pulled over yet and it is now a routine on the freeway. It's great to see a lifted, dirty rig drafting semis on the roads!

Damn XJs are bricks. Oh well.
 
since when is drafting illegal? i can idle with my civic (40+ mpg city) in 5th and not even touch the gas and keep a constant speed by drafting. as for the jeep, just put stock tires on and be a lightfoot, that made the biggest increase, even though i have 3" lift and alot of weight i've pushed 19mpg.
 
Serveck said:
since when is drafting illegal? i can idle with my civic (40+ mpg city) in 5th and not even touch the gas and keep a constant speed by drafting. as for the jeep, just put stock tires on and be a lightfoot, that made the biggest increase, even though i have 3" lift and alot of weight i've pushed 19mpg.
Click to expand...

only if you "fail to stop with in safe sure distance" and rear end someone. Otherwise i am not sure if tailgating as in less than 3 car lengths is actually illegal, IF IT IS i sure would like to see it enforced. My jeep has ben hit 5 times parked or at stop lights and red lights. Tailgaters make me nervous! I am a magnet for getting hit.
 
motorcityxj said:
only if you "fail to stop with in safe sure distance" and rear end someone. Otherwise i am not sure if tailgating as in less than 3 car lengths is actually illegal, IF IT IS i sure would like to see it enforced. My jeep has ben hit 5 times parked or at stop lights and red lights. Tailgaters make me nervous! I am a magnet for getting hit.
Click to expand...


Damn! 5 Times!?!? I thought I had a good record going of being hit 2 times in one year on the same quarter pannel....but I think 5 times has me beat!
 
My GMC suburban with a trailer and car gets a whopping 9 maybe 10 mpg with a tail wind. A few weeks ago I was coming home at 3am from picking up another mopar. I stoped at a truck stop in IN. I parked close to a couple of huge race haulers. When I came out the crews were looking at the road runner, we got to talking for awhile and I found out they were going to WI.. I asked one of the drivers if I could draft behind his rig. He kinda smiled and said sure. I kept up with them until Chicago. We were going 70 to 75 all the way. I couldn't believe it. On the next fill up I figured the mpg it was a whopping 11.4 the way there I got 10.3 with an empty trailer. I think I will get a cb for the burban and talk to the truckers from now on. Sorry for the hijack.
 
IIRC, when they tested the drafting "Myth" on Mythbusters, the results showed an improvement at even a relatively safe following distance behind a semi. To me 3-4 car lengths would be plenty close if their results are even close to correct!
 
99XJSPORT06 said:
Damn! 5 Times!?!? I thought I had a good record going of being hit 2 times in one year on the same quarter pannel....but I think 5 times has me beat!
Click to expand...

well that is since 1999-2004 havent been hit in almost three years unless you count the massive steel tube carts at home depot someone bumped my door pretty bad with. I am a magnet i tell ya. :tears: i was at a 4 lane main road and saw a guy haling ass to the red light in my mirror and pulled over a lane and avoided almost certain HARD rear ending since he barely cleared the car in front of me. You should be able to pull out such people and beat them. :clap:
 
well for what its worth I think the cold air "sucking" is gonna hurt mpg
reason being a colder air charge means a richer fuel mixture aka more fuel being used
go back to a stock "suck" setup and see if that makes a difference

dont think its gonna make much difference but every little bit helps right

replace the O2 sensors as well if you havent already
by the way
you never mentioned what kind of mpg your getting (or if U did I missed it) as of right now with all of these mods
are you a stick or auto auto is gonna be slightly worse
if your getting 24 mpg or better you have pretty much maxed out your mpg capabilities I dont think your gonna get any better and thats if your stock suspension and tire wise

I have a relatively stock 99 XJ before I put the 31's on 2 weeks ago I would get around 21-22 on the highway and between 15-17 around town depending on how hard I drive it
I have gotten 24.5 by keeping it at 65 or less on the highway and have gotten 23-24 on a couple occasions

I did gain 1 mpg or so on the highway by removing the cat conv but I also lost a good bit of bottom end tq so its a bad tradeoff in my eyes. I removed it cuz I thought it was clogging up on me
I have a new magnaflow cat on its way to me as we speak and a new dynomax catback sitting at work waiting on the cat to show up so I can get them both installed
maybe with the new freer flowing exhaust I can gain back some of the power and mpg I lost by adding 31's and the 2" BB
 
MPETESS10 said:
well for what its worth I think the cold air "sucking" is gonna hurt mpg
reason being a colder air charge means a richer fuel mixture aka more fuel being used
go back to a stock "suck" setup and see if that makes a difference

dont think its gonna make much difference but every little bit helps right

replace the O2 sensors as well if you havent already
by the way
you never mentioned what kind of mpg your getting (or if U did I missed it) as of right now with all of these mods
are you a stick or auto auto is gonna be slightly worse
if your getting 24 mpg or better you have pretty much maxed out your mpg capabilities I dont think your gonna get any better and thats if your stock suspension and tire wise

I have a relatively stock 99 XJ before I put the 31's on 2 weeks ago I would get around 21-22 on the highway and between 15-17 around town depending on how hard I drive it
I have gotten 24.5 by keeping it at 65 or less on the highway and have gotten 23-24 on a couple occasions

I did gain 1 mpg or so on the highway by removing the cat conv but I also lost a good bit of bottom end tq so its a bad tradeoff in my eyes. I removed it cuz I thought it was clogging up on me
I have a new magnaflow cat on its way to me as we speak and a new dynomax catback sitting at work waiting on the cat to show up so I can get them both installed
maybe with the new freer flowing exhaust I can gain back some of the power and mpg I lost by adding 31's and the 2" BB
Click to expand...

correct gearing will fix your loss of power and mpg. 4.10s.
 
I'm running on 30x9.5s with 3.73 gears and I'm about 150 lbs heavy from armoring - other than that, stock. On a 400 mile round trip with mixed interstate and mountain roads (no traffic, but plenty of hill climbing at altitude) I'm averaging 19 MPG - with a bunch of junk on the roof (was in the moving process. roof is clear now)
Thanks all for advice / input. Thinking I'll replace wires & o2 sensors week after next maybe.
 
You can try removing the venturi/intake silencer from your intake. I did when I first got my jeep, so I couldn't tell you how much it helped. I read this article on go-jeep and gave it a try. He documents alot of his fuel saving mods with an onboard trip computer, so I believe that removing it has given me some boost.
http://www.go.jeep-xj.info/HowtoSilencer.htm

I have a bone stock 1990 4.0l w/ auto and 235/75/15 LT All Terrains that gets me between 23-26MPG cruising on the highway at 65 miles/hr and between 11-21MPG in 4wd & in really hilly town driving with a bit of highway thrown in. I just replaced the muffler and tailpipe with a cheapo OEM replacement from NAPA so we'll see how that affects mileage. I'm in Canada, so my mileage numbers are a little higher, but still pretty good. the 11MPG that I get in town is usually if I'm driving to/from home a lot for short trips..I live at the top of a massive, 11 block hill.
 
motorcityxj said:
only if you "fail to stop with in safe sure distance" and rear end someone. Otherwise i am not sure if tailgating as in less than 3 car lengths is actually illegal, IF IT IS i sure would like to see it enforced. My jeep has ben hit 5 times parked or at stop lights and red lights. Tailgaters make me nervous! I am a magnet for getting hit.
Click to expand...

tailgaters.... :fuse: just waiting for bad happenings.
 
You must log in or register to reply here.

Similar threads

srmitchell
Why am I stuck with 12mpg? Help Appreciated
2
Replies
23
Views
2K
bentroia
B
B
Cracked block confirmed. New LB, used, LB, or v8?
Replies
19
Views
995
JeepXJFan
J
C
New engine with no start/hard start.
Replies
1
Views
988
8Mud
8Mud
S
2000 4.0 Jeep Cherokee Performance and Maintenance Advice.
Replies
7
Views
2K
CherBear
CherBear
ehall
cowl filter/intake mod
2
Replies
21
Views
8K
ehall
ehall
Back
Top