New Muffler = Lost MPG's

[Zerohour]

I would also like to point out the location of which he lives...its winter, just about dead of winter in the middle of January...a lost in FE could be completely related the the 10 degree temperature outside.

[morpheous71]

Yeah, I believe they are affecting it, there are two O2 sensors malfunctioning, I just have not had the time or parts to fix them yet. Any feedback on o2 sensors and their affect on mileage. I have read that NGK are a good company to buy them from, any input???

[morpheous71]

I have not ruled out the temp. thing yet, that's why I'll be keeping the muffler on until the spring and then running tests with the stock muffler compared to the highflow. By that time I should be a scanguage master and have better accuracy! -16 last night, working on my modifed georgeforeman tranny heater tonight...lol,

[ConnClark]

Originally Posted by morpheous71

Any feedback on o2 sensors and their affect on mileage.

Bad O2 sensors can throw your mileage way out of

[Zerohour]

*points at thermometer* My subaru runs intake temps about 20-25 degress above the external temps...at -16, I would venture to say the jeeps are no better (especially know their intake layout). He is probably operating at a 5-15 degree manifold temp. If it was zero outside for a few days he might see 1-2 mpg improvement.

My Subaru down the highway in the morning (beginning of commute) does upper 20's, on the way back (end of trip) i'm getting in the low thirties. Engine warmth is huge in winter. Hell at -16 it could be oil related. He probably has to drive 30 minutes just to get the engine up to 180!

[morpheous71]

I'll start posting some temp's, mileage, and conditions I'm driving in over the next few days. Learning so much through this site, cool, just priced my o2's $337CAD is best price for all 4, it was recommended to do all of them when you start replacing. Some feedback on this would be good, it seems like alot of money to throw at these and are they really affecting mileage that much or at least $337 worth????
I threw on a grille cover and the temp's went up around here today, my watertemp remained the same about 198-201F, the mileage seemed to get better, I was hooked up to the trailer and experiemting with the scanguage and I got an average of 17.4mpg's, this was also using a lot of coasting. More data is needed....coming soon.

[vacationtime247]

True. Same problem with my old Jeep. CEL would come on for no apparent reason. Disconnect the battery and reconnect, light stayed off. Happened 2 / 3 times.
About the muffler, you sure your not more interested in the exhaust tone than the mpg's? Know my foot becomes heavier after new exhaust. Like to listen to the sound for a few days until the newness of it wears off.
VT247

Originally Posted by comptiger5000

The Jeep ones definitely do. I've cleared a CEL that way before, and the Jeep definitely runs differently for a bit after a battery disconnect until the PCM relearns.

As far as mpg, in many cases, it's a matter of "New Muffler = Heavier Foot".

[comptiger5000]

As far as O2s, the front ones affect mpg, as they control fuel mix. The rear ones are only there to make sure the cats are working. Take a look at your exhaust, and figure out which ones are before the first cats (probably 2, if you have 4 total). Those are the ones to replace. Unless you get a CEL for one of the rear ones, or one of your cats, being bad, the others can be left as-is.

[Backtobasics]

The code should tell you which O2 sensor is a problem, but like Comptiger5000 said, the front sensors are critical for MPG. The sensors behind converters are tattle - tale sensors only.

[aggie sig]

Originally Posted by morpheous71

Well I went and did it. Put on a flowtech performance muffler onto the jeep and it seems to have dropped the mpg's by 2. Still learning the ropes of the scanguage and new driving techniques, but I swear that thing has done the opposite of what I wanted, I'll leave it on for now until I get more data and work through some other mods but come the spring I may put the old one back on for some accurate testing of both the muff's.
Frustrated!

hang out on Jeep forums, CAI's, high flow filters, mufflers, all that stuff that is supposed to increase power generally screws with your mileage in a negative way.

don't buy the Hype more horsepower doesn't just appear, it comes from somewhere, generally your gas tank and wallet.