chessplayer41

There are so many posts here and even using the SEARCH FORUMS seem to not filter what I am looking for making a new post is the option for now. Recently I had issues with my car that ended up being an exhaust leak. I got that fixed with a new CAT and the car seems to running great again but I have noticed my MPG has change. Before I was getting about 29-31 MPG or about 525 miles on a full tank, now it's down to around 22-24 MPG and about 450 miles on a full tank. I thought that maybe my OD had gone out so while driving highway speeds I put it in "I" and sure enough the RPMs kicked up..+1000 and then back down when I put it back in D. I am currently running at 2.5K RPM at 70-75 MPH. Would this be normal wear on a 2010 2.2 LT with 145K miles? ps..I am using Mobil1 Full Synthetic 20,000/Annual oil and I recently changed the tranny screen and oil.

Conax

I get about 24.5 to 25 on average in my '09 LS 2.2L and it idles smooth, starts right up and pulls well. Your RPM figures seem about the same, too. Maybe your old cat was somehow tricking the computer into leaning out your fuel air mixture and when they changed it the effect was gone.?
There are some members here who know plenty about the codes and the system in general. They will be along any minute..
My point is only that you are getting nearly the same mileage I normally get so any trouble is probably minor. How are your plugs and air filter?

donbrew

Average MPG can vary widely; one day you may get stuck idling for 10 minutes.

When were the plugs changed and with what?

Did you put a new #1 O2 sensor on, what brand, check the part number they changed at some point.

All highway 65 MPH I would expect 32 MPG, all suburban driving about 24 MPG, all city about 19 MPG.

firemangeorge

You may have a drop in gas mileage but your numbers are a little off.

The gas tank holds a little over 16 gals. So, even if you almost ran it empty.
525 div 16=32.8
450 div 16=28.1

Maybe you do have an issue but your miscalculations may make it appear worse than it really is.

RJ_RS_SS_350

I think you mean "may make it appear worse than it really is"

And as it gets hotter, you may be running the AC more, which will hurt your MPG.

chessplayer41

It's 10:45 here in Tx and I just post that...DO YOU GUYS SLEEP?? If not, GOOD. ;-) Plugs, AF, coil packs, MAF sensor, all new on prior issue/post but Conax you made a good point on the system being tricked. With all this new stuff it may be running the way it suppose yet I have noticed that when cool, I have awesome power, more than before but once I have been diving for 15+ minutes then there is some power loss, more so when taking a hill and I try to accelerate. This car ran great until I started paying attention to the MPG, RPMs, TPMS, Air Temp,....Damn readout.

chessplayer41

Also, the O2 sensor was not changed, I just used the old ones

Conax

Donbrew did ask about the O2 sensor- they do live hellish lives in the exhaust path.
With the new cat new sensors make a lot of sense.

firemangeorge

Thanks Randy. I edited my post.

Oldblue

A lot of changed parts, it'll take the computers awhile to figure out what where and if they all get along. Now one thing I do when it's time for plugs, AF cleaning, MAF and throttle body cleaning, I disconnect the negative terminal at the battery for 30 minutes, (actually disconnect, do the parts change, service, then ) reconnect.
I average 32.6 mpg.