Lostfisher1

i was hoping one of u guys would be able to help me out here. I have a 97 jeep cherokee with a 3" lift and 29" tires I don't really have a life so my drive is pretty routine lol. I go 2 work and back home and out on the weekends. I usually have to fill up 1-2 times a week depending on where our job site is. My mpg usually averages about 15.2 mpg but it has a pretty wide range between 14-16 MPG. I do have a rough idle and no check engine lite is on. I also am pretty sure my jeep is running rich because I have a sooty exhaust. U cant really see it but if i put a chunk of snow under the exhaust it is black in a minute. any ideas?

UsmclovesXJ

Well mate. Your mpg is pretty good actually...but to clean up probable causes for your rough idle id do a complete tune up BC of you exhaust. Replacing your o2 and map sensors ...im going to go on a limb here and say your o2 could be bad. Maybe a possible cat....also check your throttle position sensor. And you iac. Idle air control all on your throttle body. Also clean throttle body.....btw your mpgs are good for 29's

rklettke

Pshh I wouldn't worry about 15ish... I'm stock and I vary between 10 and 22 haha. can't wait for my left and 31's D:

UsmclovesXJ

Lol 22mpgs in a jeep lol?

Zack92MJ

I get 10 city if im lucky.

& 14 - 16 mpg thats not too off from each other. I wouldnt worry about it at all. now like 10 - 19 now that would confuse me and I would worry about it. 2 mpgs. Not at all. thats as easy as having a bad day and flooring it everywhere and next tank p***y foot it every where.

sam24th

Id run some seafoam through it and see if it helps clean out some of the carbon build up. Your O2 might also be on its way out. But in all honesty 15mpg isnt bad, on these XJs. I mean its about as aerodynamic as a brickwall driving down the freeway.

tjwalker

Some good advice here.

1. Start with fresh tuneup hardware.New Champion copper plugs gapped to .035, new quality plug wires, distributor cap and rotor. A bottle of TECHRON fuel injector cleaner in about 3/4 of a tank of gas. Clean your throttle body and idle air control. Replace your air filter.

2. Oxygen sensors have a finite lifespan of between 100k and 150k depending on the efficiency of the engine. Replace them with NTK sensors; the OEM provider of oxygen sensors to Jeep.

3. For a rich mixture, you should test the MAP sensor as well, as that is directly involved with fuel air mixture. Be sure that the vacuum line leading to the MAP sensor is pulling good vacuum or the sensor won't work.

4. Testing the throttle position sensor is also a good idea.

Plenty of time to ponder other more complex possibilities after all of the above is verified.

rklettke

yeah, I took a 900 mile trip two ways and that was the highest it got through like 5 tanks or so. my jeep seems to like 65-70