Gas mileage from a 4.0, what do you get?

[97teejay]

Newbie to the site and to the Jeep world so i wanted to find out what most people are getting gas mileage wise out of their 4.0 In-line six to help find out if i have a bigger problem on my hands.

My 97 TJ is a mod'd a little which i know will affect those numbers but after a full tune and a K&N FIPK i'm still seeing the 10-12 mark which seems low to me.

Here are my specs
1997 TJ Wrangler Daily Driver but may turn into just a trail rig
4.0L 243Cubes (is this the high output 4.0L?)
K&N FIPK with a Fresh tune on it (Wires, Plugs, Cap & Rotor)
33x10.50
3.5 Rubicon Lift
Rubicon Slip Yoke Eliminator

Any imput or tips would be much appreciated, exhaust is next to help it breathe and sound a little better. Any suggestions there would be great.

Thanks!!!

[Wrangl3r93]

I'm pushing 33x12.50's getting 16-17mpg. I'm geared down at 4.11 though.

[97teejay]

Originally Posted by Wrangl3r93

I'm pushing 33x12.50's getting 16-17mpg. I'm geared down at 4.11 though.

That's a pretty big difference, if you were geared down. Wouldn't you get even less miles per gallon? (higher RPM at lower speed) I have a fealing that something is not right.

Thanks for the imput

[southtj]

I've got 31's and 3:73 gears and get 14-15 city.

Have you corrected your speedometer since you put the bigger tires? If the speed is off that would throw off the mileage.

[TerryMason]

Do you have a manual or auto? That makes a big difference. The gov doesn't have info for a 97 online, but here are the gas mileage stats for a 1998 Jeep Wrangler:

Engine & Trans	City	Highway	Annual Cost
4 cyl, 2.5 L, Manual	16 city	18 hwy	$3343
6 cyl, 4.0 L, Manual	15 city	19 hwy	$3553
4 cyl, 2.5 L, Automatic	15 city	17 hwy	$3553
6 cyl, 4.0 L, Automatic	13 city	16 hwy	$4059

* Based on 45% highway driving, 55% city driving, 15000 annual miles and the price of fuel used by the vehicle.


I personally get 13.6 MPG

Date	MPG
10-Nov	13.92927176
15-Nov	15.72286013
20-Nov	14.98198369
23-Nov	15.28729573
30-Nov	14.15187054
7-Dec	13.7106826
17-Dec	13.51619956
24-Dec	13.94557823
30-Dec	12.51727845
6-Jan	14.49840713
11-Jan	14.20560748
11-Jan	18.11965812
11-Jan	14.30948419
20-Jan	16.30434783
25-Jan	13.96172444
3-Feb	13.65649606
12-Feb	14.07641482
15-Feb	14.00147384
22-Feb	13.91663796
29-Feb	13.07989691
3-Mar	13.18565401
13-Mar	15.91686398
23-Mar	13.0560603
4-Apr	14.2373747
13-Apr	12.8758087
22-Apr	13.11299926
27-Apr	13.49838678

South's right about the speedo. If you put on larger tires, you'll travel farther with every revolution, and your speedo will report you going slower than you really are. You'll also show less miles on the odometer.

[Wrangl3r93]

Yeah put in a speedometer gear from quadratec and verified it with a gps. It's dead on. Most, but not all, of those miles are interstate. I drive from Murfreesboro to Knoxville for college. I checked again yesterday. At 80mph I got 15mpg and I drove 70 the whole way home but haven't filled back up to check again.

[97teejay]

Thanks for all your info guys! It makes me feel a little better about it.

I just learned on the way home that my speedo is off (the city cops set up one of those speed trap signs). The previous owner put the lift and tires on then he sold it.

Terry, thanks for the great info. It is a 5 speed manual.

The gear doesn't look too technical to install, and thanks for the tip to the quadratec site.

The only thing i can't figure out for sure on is what gears do i have to determine which speedo gear to get. i'm 99% sure they are stock. But i've read that they could be 3.07 or 3.55 gears from the factory when i do a search on the net. Any way to tell for sure or do i need to do some digging?

The quadratec site gives me this info which helps a lot
Protect your Jeep while rock crawling with side rocker panel guards & skid plates from Skid Row Automotive, Body Armor, Rugged Ridge, Olympic 4X4 Products & Warn. - Quadratec

thanks again for your time everybody!

[Wrangl3r93]

The speedometer gear takes a whole ten minutes to change. My searching skills fail me now but there has been a thread about where you can put your vin number in and you'll get an e-mail with everything that jeep came with from the factory. There's also a tag on your differential, mine was on the front axle before I broke it off, that has the gearing stamped onto it. Or you could always jack the jeep up and do it the old fashioned way turning a tire and counting the revolutions of the tire vs revolutions of the driveshaft.

[97teejay]

wrangler93, thanks for all the insite...

That site would be cool if anybody comes across it, post up the link.

Sounds like a simple DIY for the speedo gear so i'm on a mission to figure out what gears i have so i can get that speedo gear ordered up. I will check for that tag tomarrow morning, i'm done for the night. Too much parting memorial day weekend.

later!

[97teejay]

Finally Found the tags, 3.07 gears stock, should i think about re-gearing with 33 12.5's?? This is going to be a in-town commuter / trail rig. but i would like to still take it on the freeway to get the trail..

There are a crap load of options, let me know what works for you.

THanks!

[TwistedCopper]

Last time I checked my 4.0L YJ it was roughly 17 mpg. This is with a 3 speed auto and 31" mudders. This is 70% highway.

City driving is really bad, I never checked it but the fuel goes real quick in stop and go driving.

[Bounty__Hunter]

Originally Posted by 97teejay

Finally Found the tags, 3.07 gears stock, should i think about re-gearing with 33 12.5's?? This is going to be a in-town commuter / trail rig. but i would like to still take it on the freeway to get the trail..

There are a crap load of options, let me know what works for you.

THanks!

For ease of installation, consider a set of used axles from a 2.5L 5spd TJ, they'll be 4.10 gears and bolt right in. You can usually find them for $400 a pair or less.

[97teejay]

thanks for the info!! I think for now i'm going to leave the gears alone and see how they pan out for me.