Hmmm so you had just the cross bars. Not like a big rack that holds a tire and rack and all.

 

multiply your odo trip reading by 1.22 to get the correct mileage you've driven. Basically, if your odometer trip says you went 100 miles, you really went 122. Somebody on here did all the math out for calculating the difference and it was accurate, so that should tell you what your true mpg rating is.

Your o2 sensor (right at the cat) can be a big factor too. Pull your injectors and clean them, or get a set of 4-hole's from a reliable source on here. It's tough really finding what's causing mpg losses just because it can be multiple things.

I average about 11 in the city and 14 hwy, maybe 15 if I can tuck in behind some semis and have a tailwind too, but I'm on 4.5", 33x12.5 BFG M/T's, and 4.56's with an auto, so it's really not a terrible mpg rating for what I'm driving.

 

Idk if my speedo is off though. I'll check it tomorrow with my phone.

 

yea nothing fancy. i had a full exhuast then too. i think ima do a brass cap and rotor, some livewire plug wires, new spark plugs soon. and switch back to 10w30 oil.

im running 5w40 rotella t6 right now and i lost some mpg with the heavier weight for sure. so ill probly do rotella t5 10w30

 

You ever replace the speedo gear after going to 31's? If not, I'm betting it's off considering you've got 3.55 gearing.

 

Cool. Yea I was gonna run this take and another then take the rack off and see what happens.

 

I didn't bc I just bought the jeep about a month ago. It already had a 3 inch lift and 235's on it. So I don't know if the previous owner/owners ever changed it out.

 

ill probly get rid of the rack too. i dont really use it so theres really no point in having it. i put it on cause it was free off my parts jeep but ill either give it to my buddy or sell it. we'll see

 

Yea they look good up there but if it's giving me a 2-3 mpg drop then that thing needs to go till I can make some mods to adjust for it. Lol

 

When mine was stock I got around 24mpg with a 5spd.

 

235's (just shy of a 30") don't make much of a difference as compared to stock (29") tires, so I highly doubt they ever changed it out. It's an easy, 10 minute job to do though. Pull the gear and if it's a 34 tooth, it's still stock. With 31's and 3.55's you should be running a 32 tooth speedo gear to be accurate.

This is huge for mpg's. A roof rack, though cool, is like a billboard on top of your XJ. If it's not being used and you want better gas mileage, pull that thing off.

 

Ok so I hooked up my gps and the mph is almost dead on. When my speedo said 70-71 the gps said 71-72.

 

Again, probably rural and as stated, with a stick.

 

fact remains. getting 13 mpg is terrible. a few guys at work have xjs and the consensus is 18ish. one of them has a 3" lift and 31s. he said he gets 18 no matter what. but it is a nice cherokee. 110k mile 98 sport aw4. I'm kind of jealous.

 

True that I am near due for a tune, but, 45-50 minutes to go 7 miles in bumper to bumper kinda negates.

I still have my orginal window print which I believe put the estimated at about 14 or 15 city. So, averaging 14.5 in a 15 year old truck with 200k, not bad in my book. (and I have a Chicago temper, so some driving is not exactly conservative)