edman2007 Posted October 30, 2008 Share Posted October 30, 2008 Ok, my 5 speed 2wd 4.0l mj is getting around 15 mpg right now :hmm: (easy driving) seems a little low to me. It has 235 tires with stock gearing (around 2k rpm in 4th at 55 with tire size compensation). The exhaust is a little open with a glass pack and cherry bomb turbo muffler (stock pipe diameter). Ran seafoam recently to clean out fuel system. Going to replace the O2 sensor, anything else i should look at? Thanks, JD Link to comment Share on other sites More sharing options...
DansGreyMj Posted October 30, 2008 Share Posted October 30, 2008 Cap, rotor, plugs and wires. Link to comment Share on other sites More sharing options...
FxRacing282 Posted October 30, 2008 Share Posted October 30, 2008 Link to comment Share on other sites More sharing options...
BLHTAZ Posted October 30, 2008 Share Posted October 30, 2008 Is your speedometer calibrated correctly to the 235 tires? If not, your calculations may be off a little. I agree with making sure that all the tune up stuff is fresh along with the o2 sensor. I saw an increase of just over 14% in MPG when I replaced my injectors with some of these... http://www.precisionautoinjectors.com/p ... roductId=7 I have a deal set up with that guy for us too. Be sure that if you buy from his site that you use ' JEEP ' as a discount code at check out for a 10% savings :brows: Link to comment Share on other sites More sharing options...
ComancheKid45 Posted October 30, 2008 Share Posted October 30, 2008 Ive only been calculating about 13mpg with city driving....i have 30x9.50x15 tires so i know thats gonna throw my speedo off but i don't know if i should be worried. Following is done to my Truck (4.0, AT, 4x4) Precision Injectors New Plugs New Wires Cone style Intake Tornado style insert (i think is BS but i only payed $4) Link to comment Share on other sites More sharing options...
Pete M Posted October 30, 2008 Share Posted October 30, 2008 Tornado style insert (i think is BS but i only payed $4) Don't "think", know. Why do people install freer flowing heads, exhaust, and bigger throttle bodies? Stuffing a plug into the system won't help with power. But it can help with fuel mileage. Just imagine that you can't push the gas peddle all the way down. :yes: Link to comment Share on other sites More sharing options...
Randy in Maine Posted October 30, 2008 Share Posted October 30, 2008 You have geared your final drive up an additional 4.3% with those 235/75/15 tires over what came stock. I think you can test the correct voltage output from the O2 sensor if you go over to the Renix link and test the plug under the hood with your volt ohm meter. I have yet to hook up my LM-1 to the jeep to see how close it is to what it should be though. I did have my injectors cleaned and calibrated a few years ago at www.cruzinperformance.com for cheap money and it certainly improved the performance, notably down at low speed. I also tested the fuel pressure then and it was what it is supposed to be. I still only get about 21 mpg with my 5 speed and 4.0L running 3.07 gears, stock Michelin 215/75/15 tires though on the highway shifting at 2K. I am going to check my O2 sensor here soon to see if I can do a little better. Link to comment Share on other sites More sharing options...
edman2007 Posted October 30, 2008 Author Share Posted October 30, 2008 Yeah, i have been calculating with a -5% error in mileage. (if i go 100 miles on the odometer, then it is really 105) I'll be going through all of the tuneup stuff and come back with some results. Hopefully they are positive :thumbsup: Link to comment Share on other sites More sharing options...
Oizarod115 Posted October 31, 2008 Share Posted October 31, 2008 replace the tune up parts if they're old, but you probably won't see any fuel mileage out of it... it's just a good idea to keep things running smoothly. i went from 16-19 mpg by replacing a defunct o2 sensor. paid for itself in weeks. buy the dealer piece or a bosch. don't get the hack-n-tap one. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now