Mattster

I've been getting 11-12mpg for awhile and suspected it was the o2 sensor. So I changed it out on Thursday, surprisingly easy took like 10 minutes to change. Ran a little smoother, the old sensor was brown colored. Usually only get 200 miles to a tank. So after driving 40 miles and being close to the full mark I thought my MPG was good again...wrong. Before changing the sensor I would run Lucas Fuel injector cleaner and that would boost me to about 19mpg for the first 40-50 miles, but then it would drop off and suck again. After changing the sensor, it hasn't improved MPG really at all, I am at 1/2 tank and am about 110 miles which is about 10 miles further than I normally would go. But it seems like the first 40 miles it does good on MPG but after that it falls on its face. After driving 40 miles the other day I filled up just to see how much would go in and could only get 2 gallons in there.

Planning to change the fuel filter this week depending on how much money I got, Dodge is in the shop sucking up money. What else could be causing this poor MPG? Catalytic Converter? how could I tell if that was the cause? Fuel Pump? Map Sensor?

I recently upgraded to a Hesco intake system, new plugs and wires.

bamorgan7

i have the same problem i get 13 mpg all stock and i changed both o2 sensors a week ago

kilbrethj

how are you reading your mpg? just by the gas gauge? because my gas gauge goes down wicked slow when it is full and faster as it gets less full. but, when I'm almost on empty i can still only fit about 14 gallons in my 20 gallon tank... so using the gauge to do mpg is not very accurate. what you should do is fill it up till the pump clicks off twice. then drive 100 miles and then fill it up again at the same place till it clicks off twice. Then take how many gallons you've used to drive the hundred or so miles and divide it into the hundred miles. theres your mpg's. By the way i was getting 16.7mpg before my new o2 sensor and coil now I'm getting about 15mpg now.

01blackxj

Yeah dont just use the gauge to measure your MPG because the gas tank is odd shape so the gauge will stay in a spot for long time and then just suddenly drop off. I am all stock and am only getting about 12 MPG but that is all city and no highway

jpdocdave

i use the mileage, divided by how many gallons it used, i think thats what everyone is basically saying.

i did complete tune up (cap rotor plugs and wires), fuel filter, air filter, and 02. and i get 12 mpg in the city

i got just over 20 on the highway keeping rpms just under 2 grand about 62 mph. this is with 31's so maybe there's a half to one mpg better i'm getting than actual readings.

if i were to keep my foot out of it from the stop lights i could do a little better, but i don't hot rod, just keep up in traffic. bottom line, jeeps do not get good mpg.

edit: my state of tune and all was not terrible, but it had been a while for a tune up, and 02 looked original, and i saw no real difference, in replacing these parts. kinda disapointed, but obvioulsy keeping the tune up is important, but mine was about 5 yrs old on tune up parts, and it didn't make a dramatic difference. and i am the biggest person on maintenance you'll ever find.

kilbrethj

WOW jpdocdave, that is a big stretch!! LOL 12 to 20 mpg.. haha i guess that is about right though... mine is about 15 with half city and half highway.. haha

jpdocdave

yep, when i'm trying to get to work at 6:45 in the am, i'm trying to get away from the idiots on the street. when i hit the highway, i try to get the best mpg possible. i used to fly down the highway at 75-85, freeked out if i saw a cop, worked the crap out of my engine at 3 grand or more, and got there like 20 mins quicker, and used a lot more gas. now i kick back in the right lane, at 1950 rpm, watch the yahoo's hitting the brakes who just flew around me, and i get 20-21 mpg in a brick.

Mattster

I calculate mileage by dividing the number of miles by gallons put into the tank. I don't use the gauge as measuring just stating that after 50 miles I would have used 1/4 tank according to the gauge.

GTPstarter

Now you guy's have me worried. Next week the old girl is scheduled to have her o2 sensor changed. (Ah the luck of the recall) Anyhow, as we speak I've been getting 20 to 21 on the highway and 16 to 17 in town. The key to that was listening to what I've read on these boards and KEEP it UNDER 2k on the tach. Next week after the o2 sensor goes in I'm hoping to change the plugs too. The other reason I think I get the good gas milage is the 5 speed. Once I'm in high gear on the highway and at 70 mph, I'm only at 16/1700 on the tach.
Does this make any sence to you guy's ??


GTP

jpdocdave

absolutely, i can't believe that gearing though. 70 mph at 1700? i'm jealous. its all about gear ratio in axles and trans though. i know they say 5 spd gets better mileage, but its amazing the difference it makes when you operate the jeep in its effeciency range.

what are you worried about?

GTPstarter

Jpdocdave,
I scewed up on the quote about the 1700 on the tach. I double checked and at 70 it's around 2250, still all and all it seems to ride a lot free'r in high gear more than any of my other Jeeps had.
What I'm wooried about is the MPG going out the window after the o2 sensor gets changed.

jpdocdave

i think the only change that could happen is better, not worse.

northline76

Ive been getting 10mpg on 30s with stock gearing and it sucks. Had the codes checked today and nothing came up but I know the 02 sensors will need to be replaced.

Check your tire pressure also!

I checked mine and its nearly 10psi to low, which is prob a reason why I have been getting such crappy millage.

motoxpete

I just did the same tune up without the o2 and i seem to notice a nice difference... i haven't ran a full tank to really be sure but the needle isn't dropping as fast.... we'll see tho