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i know another MPG thread but i just cant figure out why

J

jeeptorino68

NAXJA Forum User
Location
Lebanon OR
why am i getting such poor mileage, i have replaced my plugs wires and car, somewhat recently, O2 sensor like 3 weeks ago, i have a 99+ intake manifold, and bored TB K&N drop in filter, and dynomax exhaust, with magnaflow high flow cat. just replaced the clutch fan t stat and radiator everything comes up to temp fine. i run 30s (2 in BB) on 3.55 gears and an auto tranny, im not hard on it, so what the heck gives???? it makes no sense that i get like 13 -15 combined mileage. any ideas? anyone?

maybe something like the TPS? or would that even affect it? any other sensors like that that would affect my mileage?
 
sorry to say it, but that's pretty normal on an XJ... if more of oyur dirving is city than highway, that makes a big difference... driving it hard doesn't help either.
 
yea most of my stuff is city, but i still thought it would be better then that, its not too great on the highway but maybe ill have to live with it
 
Put 235's back on it, they still look pretty good with a 2" BB and other than factory offset wheels. 30's put a hurtin on my gas mileage before I regeared.
 
When I got my '01 it was on 235's and the Up Country suspension (1" over "normal" stock hight) I was getting 20 / 21 average. My driving is mostly mountain roads & hiway, maybe 15% city. I corrected for the tire size before calculating the mileage, are you doing that?

With the 4.5" lift and 31" tires I'm getting about 17, again corrected for tire size. I'm still at 3.55's and expect better mileage and performance once I go to 4.10's.
 
also, an older engine won't get as good of mileage as a newer one... like say DougJ's '01.

Tires definately make a difference. you do need to calculate the difference in mileage... with 31's, the difference is about 10%. Meaning that you go 10% father in one rotation than with stock size tires. so if your odo reads 10mi., you've gone 11. make the changes, and that can help.
 
my 90 xj just drove to vegas from my house filled up 20 gal tank, 300 miles filled up again there used 15 gallons. So it got around 20mpg. I was going 75-90mph. All stock with a mangaflo muffler. 5 speed with 3.07s.
 
Different Jeeps will get different results. I had a 3" lift, 31s, 3.55s, and 330k miles and I was still getting 20 mpg highway and at least 15 mpg city ('91 XJ). BUT, I drive extremely conservatively (soft take-offs and try not to exceed 60 to 65 on the highway).
 
I just drove about 500 miles in my xj... 4.5" lift on 31's... and it was loaded down with camping gear, and kayaks, and mountain bikes... I think I got like 17mpg ish... I didn't do the exact calcleations, but it was rough, in my head... I'm not a easy driver... I was doing about 70MPH all the way, up until the mountains, where I know it killed the average... slow, tight 20mph turns... I'll do da math on the next fill up.
 
Do a complete tune up.
 
ive done all the tune up stuff recently, i guess im not factoring in the tire size change, but i know (or thought i know) that at about 100 miles im off by ten i think? maybe ill have to find out what my stock tire size is, i think it was 225 75 15
 
should be that or 215/75 R15... off ten at 100mi should be a pretty close estimate... factor it in, and that's almost another MPG and a half!!! (by really rough estimation...)
 
Has anyone tried the hypertech computer programmer?

http://www.hypertech.com/

max%20red-320x513.jpg


They promise power and mpg increase! Sounds like $400 snake oil to me.
 
I don't have the Max Power thing, but I have the Powerprogrammer III. Before I lifted my XJ the economy setting did help. After the lift the economy setting doesn't do so good. Around town its ok but on the highway you can barely hold 65 w/ a head wind.
The High Test programmer is alittle better, I can hold OD pretty well on most hills, but w/ the price of the gas it really isn't worth it.
I'm using the economy setting and I'm getting about 16mpg with a 3" and 30's.
 
I've got 245/75/16s and 170K with stock 3.55 gears and get 13-14 city and 20 highway. I also drive conservatively which I think is the most important factor. I experimented on one tank and drove 70-75 highway (getting up to speed quickly) and accelerated quickly from lights and it dropped to 12 ish city and 15.5 Highway. All speeds and miles were measured via GPS.

My advice, try a tank driving like an old lady and see if it makes a difference before you dump tons of cash into it.
 
good call... try it!
 
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