Low money and high dreams

OK so in one month I leave for college and I would like to take my xj with me. I'm currently getting 11mpg. I have 31s on it with the stock gears and stock everything else. Semi fresh tune up. Any ideas on how so squeeze a little more out of it? Without killing the bank. My college is 400 miles away so that's the issue here haha.

GregGA

It's probably not what you want to hear, but re-gearing is needed with 31's. I run 4.56 with my 31''s, but you could get by with 4.10's.

Is 11 around town? I get about 16 with mine, but I am very light on the pedal. Freeway is 18 at 70 plus.

An XJ is not a Prius ,but you should do a little better than 11. Have you checked your plugs? Running rich? Drive about 55 going to college. It makes a big difference slowing down, but watch out for semi's coming from behind

Low money and high dreams

It's 11 just cruising at 55 all country roads. If I could get 15 out of it I would be a happy camper. I thought about doing the 703 injector swap. And I think it's running rich you can smell the gas just getting thrown out the back. Oh and I don't have much of an exhaust. It stops right after the cat but it's an 89 so there no o2 sensors back there.

XJmike0122

I'm running 33's with 3.5 inches of lift and get better mpg than that. Here's my tips. Tune it up. Turn off the A/C and ease up on the skinny pedal.

Edit: On stock gears.

Fred/N0AZZ

FYI when I finally switched from the stock 3.55 gear to the proper 4.56's for a 33" tire my MPG's increased just over 5 MPG with that alone. It was not much difference when it had 31's on it when I bought it.


Now with a 4 1/2" lift and heavy with cargo, armor, winch/bumper, swing out tire carrier bumper, 33x12:50x15's city, highway I get 15.9 MPG. This is with the original engine and trans 226,000 mi. 4.0/ AW4.


A gear change is the only thing that will help you at this point and remember your trans in overheating with the stock gears also and the 31" tires, up/down shifting.

rgr4475

My suggestion is to drink the cheapest beer possible (Not even sure what the cheapest is, Natty Ice still the go to?) once you're at college and save the rest for gas money and condoms.

MonacaYankee

I have 31s with 3.55 gears and a 3 in lift. I get about 14-16mpg.

Cheapest would be to change back to smaller tires.

My stock 2wd jeep gets 21-22 mpg interstate only driving at 65.

Low money and high dreams

Love the advice

BlueRidgeMark

Forget that. First, fix this:


And this:


You have an engine problem. Fix it before you try to polish a turd.

You have a malfunctioning (yes, I said malfunctioning) exhaust system. Fix it before you try to polish a turd.

Your exhaust system does a lot more than just get the exhaust gases to the back of the vehicle. It's a SYSTEM, not just a collection of parts. A properly designed exhaust system works with the engine - take it off and things won't run properly.

Fix your broken stuff before you look for tips to improve your gas mileage. You'll probably get that 15 you are looking for, or close to it.

THEN worry about fine tuning it.

Low money and high dreams

Even before the exhaust system came off it still got 11 to the gallon.

DFlintstone

Has your speedo been re geared for the 31's? Using long sections of the county mile markers and my odometer I figured out to add 4% to my miles before dividing by gals. (you might be able to add more)

Always a good idea to keep an eye on that MAP tube. Also see Cruisers tips ontop in my signature.

There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage and it will be pig-rich. (black smoke, fouled plugs). You can pull the line off the MAP and feel for vacuum with your finger.

Low money and high dreams

Thanks! That makes the new economy go up to 12!!! That makes total sense about the 4% calculated it out to an extra 43 thousand feet per tank. That's a lot of unaccounted distance.

DFlintstone

4% was just for me! You need to figure out if yours is correct or not, and if not, how far off is it.

I have 235's. If the conversion charts were correct that would mean mine came with 215's or something. I just used the mile markers to figure I'm 4% off. (so to drive 50 MPH I put the needle on 48), or if it says I went 300 miles I went 312.

Yours might be 3 times that, Idk. Besides the map tube and cruisers tips, your 02 sensor is a big player for mileage also.

cruiser54

I'm with Mark on this. And Flintstone.

Do my Tips 1 through 5. Free.

Spray carb cleaner around the MAP to Throttle Body tube. Make sure intake manifold bolts aren't loose.

What's a "semi-tune-up"?

I hope in college they teach you how to approach things systematically, logically and with the correct data.

wcw4496

I have a 7.5 inch lift and 33s. Regeared to 4.88s and get about 10 miles to the gallon