Rakkasan_Jeep

Well, I replaced the plugs about 2 months ago, PCV valve and fuel filter. First few tanks of gas I was getting great mileage.. about 19.9 miles per gallon on average, but I was also traveling 60 miles a day for work. Since the last month, my job transferred to a new shop, mileage went down to about 18.7 but I'm burning gas horribly.

Air filter is fine, it's a K&N and my truck starts fine. Thinking it might be the O2 sensors finally going. However, I'm not getting any check engine light. Or is it possible that the sensors are getting clogged up and at the point where they need to be replaced before the check engine light comes on?

A little FYI I'm running an 03 , 4.7 with about 178k on the factory O2 sensors.

Bustedback

O2 sensors do not get clogged up. They do get a little lazy and don't switch as fast as they used to. You need to get a hold of a scan tool and watch the data stream to verify the O2 sensors are working properly. Don't just throw new sensors in blindly without checking things over first.

Rakkasan_Jeep

I'll have it checked at work tomorrow. That's about the only thing I could think of knowing all the crap I replaced when I did the tune up.

dnuccio

18.7 is still pretty damn good. i wouldnt be complaining

Thexjfiles

Id replace the O2 sensors with factory units. Thats a ton of miles on originals.

Rakkasan_Jeep

It says 18.7, but it's not reality. Reality is maybe like 8-9 to the gallon.. hell maybe less. I know I killed 1/8 of a tank in 30 miles and it's never done that.

dave1123

If you're using the overhead display for average mpg, you're kidding yourself. My WJ 4.0 gets about 16 to 18 mpg on the highway and about 12 doing my paper route, that's stopping and starting about 400 times in about 45 miles. This will go down to about 10 once the temp get colder.

I was looking at the gas pumps today and I noticed the Super Premium doesn't have ethanol in it. I could probably get better mileage using it, but my wallet would be much lighter!

My personal opinion is go back to the original air filter and air box. That unit is designed to take in cold air from in front of the grill, not under-hood heated air and the pad filter will pass over 5 times what the engine needs to breathe. Another thing you can do is move the IAT into the intake ductwork before the throttle body, not in the manifold.

If you're measuring your 1/8 tank from full, remember you have to draw off a lot before the tank float starts to move and the guage response may not be linear. When figuring mpg, it's always best to use the fill, drive, and refill method.

I'd also replace the 02 sensor with a guality one. Mopar or Bosch, IMO.

Rakkasan_Jeep

Well after my tune up, my mileage was awesome. I did think about the O2 sensors since the factory ones have that many miles and figured replacing them might help. I can't put the stock air box back in. After moving about 20 times in the last few years I've lost track of the pieces and parts. I replaced the IAT a few years back and no problems with it. Problem is finding a gas station with straight gas and none with the ethanol added.

Rakkasan_Jeep

Correction, it was the TPS and IAC I replaced a few years back. I had a weird incident last night that though. I was dropping off some Redbox DVD's and on my way back home, hit a stop light. As I was taking off, my upper console display went off saying "low coolant", impossible I thought. The over flow tank is full and I've never had any issues with that sensor.

When I got home, I popped the hood, check the tank and it was fine, then I pulled the IAT and wouldn't ya know, 10 plus years of gunk on the damn thing. So next week when I get paid again I'll replace that and also flush the power steering with the correct fluid..