mattphillips90

Hey guys, so I havent had my cherokee too too long and since I got it Ive been doing tune ups to try and better my gas mileage. Ive tracked my miles a lot and Im pretty much getting 12 mpg. Not running any large tires and def dont race my jeep. I just changed my plugs amd wires and I havent been able to track my miles since I did but my old plugs werent too bad so I dont suspect a giant boost there. I do have a cracked exhaust manifold but my new one will be here monday but im not sure if it would cause a big issue with my o2 sensors or not to waste gas. Just wondering of anyone has ever had any gas gauge issues? My gas gauge always seem to act weird. I get normal cherokee has mileage when im over half a tank, like 16, but when it gets to about a quarter ot drops on like 15 miles with the last eight lasting like 5 miles or so. I know the gas gauge is not an accurate instrument and I feel I may be gettong normal gas mileage and my gauge may be broken showing its empty before it actually is. Only thing is, I hate to drive around on E just in case. When I fill up I normally get about 17 gallons so I guess that leaves 3 unaccounted for but idk guys any help?

mattphillips90

Please ignore the errors, I posted this from my crappy phone keyboard

Fsher21

I guess I may be confused but how are you basing your mpg off the gauge and the fill up? Just reset your trip odometer every time you fill, then divide by how many gallons you put in. I get about 180 miles every 13 gallons roughly.

you could have a bad float or sender in the tank relating to the gauge being off.

mattphillips90

Yea thats how I track it, with the odometer. I just know some 8ths of a tank last for 35miles then the lasr eigth is gone in 5

Fsher21

Yeah mine is a bit funky like that, i just watch for the light and make sure it comes on at a consistent number of miles traveled. It is annoying but fixing it may be more work than it is worth.

mattphillips90

And all together I get about 240 to a tank

mattphillips90

Yea it really is annoying I just want to make sure its not saying im on e before I actually am

Fsher21

you should have a 20 gallon tank, and the light comes on with around 2.5 left. If you fill up right when the light comes on you should be putting in just about what you are now. Just watch to see if the light comes on at a significantly different distance traveled than before, suggesting the gauge is getting more inaccurate.

If you insist on finding out, throw a few gallons in the back and drive until you run out. Then all the crud from your tank goes into the filter lol.

mattphillips90

Haha I thought about doing that but yea like you said, there are negative consequences haha

chaddwick2005

Just to let you know, the o2 sensors play a huge part on an engines air fuel mixture. Normally for OBD-II vehicles there are going to be 2 o2 sensors, one before the cat, and the other behind the cat. The o2 sensor before the cat plays the biggest part, it reads the amount of oxygen left in the exhaust gas after combustion. So if you have a cracked manifold, exhaust air will be escaping, giving that o2 sensor a false reading. Which in turns tells you computer the wrong calculation and your computer will either richen or lean the air fuel mixture. Whenever you are running on non-ideal running conditions (i.e. faulty o2 sensor reading, bad plug, clogged air filter, old fuel filter etc.) you will be wasting gas. So I would wait until you change the manifold and then see what your mpg are. If they don't change, give the jeep a whole tune-up, you already did the plugs, do the air and fuel filter next.
Another thing I noticed in my fiance's car, whenever her car is up for an oil change, she gets worse mpg's, but after the oil change, there is less friction between the cylinders and the piston rings, so her mpg's go up, so maybe do an oil change as well. Check diff fluids as well.
Just my 2 cents
-CZ

Turbo X_J

If you never let it drop below 1/3 tank your fuel pump will stay cooler & last longer.

mattphillips90

I bought the jeep in feb and I did the oil, diffs and air filter that week. I was afraid they hadnt been done but sounds like the manifold might be my best beat

macgyver35

My gauge does what your does. A full fill-up will actually put the needle above the full mark. It takes about 65-70 miles for it to drop to 7/8 of a tank. However, the last quarter tank, as read by the guage, disappears in about 15-20 miles. Based on a 20 gallon tank and what I put in when I fill up, I'm guessing that I still have about 4 gallons left when my gas light comes on. I'm getting (with a newly remanufactured engine) about 13.5-14 around town, and with the cruise set on 65 I get about 19 on the highway.

It's a damn good thing I'm good at estimating the increasing rate of drop or I'd be running out of gas once a month.

You'd think after all of these years, getting a gas guage to read halfway accurately would be a no-brainer for the auto industry. I mean hell, we put a guy on the moon nearly half a century ago, and I have a cell phone that's so stinking smart I almost don't need a computer for anything anymore. But the gas gauge thing has us stumped?

mattphillips90

Haha if I had the money to keep it above 1/3 I would but a lot of times Im crossing my fingers just to make it to school and work.

Yea you would think, of all the sensors they use, it would be pretty easy to make a sensor to read an accurate amount instead of a floater