I am boggled by the MPG I am getting with my Jeep. It is a stock Jeep with 235/75/15's. I am going to go 3" and get 31's but I would like to figure this out before I do that so I dont get 10 after I do my mods.

This is what I have done to the Jeep latelty -
Recent new items Cat/Muffler/Tailpipe/Cleaned throttle body/new air filter/oil change/engine tune up plugs/wires/cap.

What else should I look at? There are no lights on the dash for engine or anything. Also sometimes I have to crank it a bit to get it to start.

 

after i got mine. i gave it a better air filter. its not a huge power increase but you can hear it sucking in air.
and i havent tried it but i hear a boared thorttle body helps alot not a spacer

 

I cant get an air filter like that. I would want to but I drive about 8 miles on dirt roads every day to work. It would get very dirty very fast after just a week. I bought my jeep for a work vehicle because these roads get very nasty in the rain and winter.

Also after I cleaned my throttle body it seems the engine revs louder on startup and when I put it in park. It sounds like the thorttle body is stuck open some? Does this sound like it could happen? Do I need to clean it more or something? It never did this before I cleaned it.

Any other ideas on MPG?

 

You dont need an air filter like that it is absoulotly worthless ,go buy a k&n filter for the factory box and you'll be better off by a long shot.

 

INJECTOR SWAPP

 

injectors or re gearing..other than that the biggest thing that will help is smaller tires, alloy wheels if you have steal ones, and most of all...a FULL fluid change.

 

I am getting 13 too, I have 32's and pretty sure new injectors and a hi flow cat and new muffler will really help me out. The next step i think would be regearing. Money money money

 

Does anyone know if a cracked exhaust manifold/header would cause lousy gas mileage?

 

Certainly will.

 

This

 

Looks like I know what I'm saving up for next then, thanks!

 

Does it rev really high and stay that way until you restart it a couple times? Revving so high it sounds like its about to take off like a jet?

A fairly common problem causing this is either the IAC (Idle Air Control) or the TPS (throttle position sensor)

I don't know if this is true in your case but I do know it is a common issue.

 

I can get 13 if I drive the way I like to drive...but I get 17 by behaving myself.

BTW, I took a K&N off my f350 when I read a review in Motorcycle Consumer News on them. K&N is very big in the motorcycle world...and MCN is the Consumer Reports of that industry. Not to burst any bubbles but the reason K&N produce more "power" is larger holes in the filter media and allow more airflow. But the larger holes allow more dirt...way, way, more dirt.

The concensus is this: use K&N if power is more important to you than engine life. USe the factory filter if you want the motor to live a long and happy, if 4% underpowered, life.

 

I fixed my cracked header last week and i didn't get any increase in gas mileage.

 

did you reset the ECU after you did all this stuff?