acn684

Car history: 2006 - 63,000 miles.

Car Mileage History:

New, stock everything: 27.5 mpg average 50/50 city/highway.

~30,000 miles: heavier potenza pole position tires - 26.5 avg 50/50 driving:

~60,000 miles: 60/40 driving - averaging 24.5 mpg.

~62,000 miles: O2 sensor goes to crap, car goes through 2-3 tanks of gas before switching, mileage with dead O2 sensor was 14.5 mpg 60/40 driving.

~63,000 miles: replaced O2 sensor, oil flush, average mileage is now 19.5.

~63,000 miles: changed all spark plugs to new, average is now between 19-21. Noticeable increase in mpg highway but accelerating from dead is killing mpg.

Also, I reset the ECU after the spark change by taking out the fuse for a minute and putting it back in.

I thought the spark plugs would help the mpg a lot considering it was running rich for about 500 miles. What else should I look into? I'm considering seafoaming it, but there's too many mixed opinions about that.

Any thoughts?

nj2pa2nc

I do mostly highway driving but drive conservately-my racing days are over-rather not have to worry about speeding tickets which makes your car insurance rise. I average over 30MPG.

acn684

I used to average 25-26 mixed driving; Its low because of tires which are heavier and stickier and also I have a Yakima rack on top with deflector.

But after the O2 died and replaced, its been struggling to keep above 20.

C25A1guy

How are the tire pressures? Maybe playing around with the tire pressues +/- 2-3 psi might bring some MPG back for you.

acn684

Pressures are higher than recommended

Set to 33/31 instead of 32/30. If anything, I should get better mileage like that. I don't want to go higher though as it seems to get "floaty" at one point.

C25A1guy

Other factors I can think of:
-Dirty ATF if 5AT
-Slipping clutch if 6MT
-Valve adjustment loose
-Sticking brakes
-Alignment
-Using heavier oils then recommended
-Dirty air filter
-Winter blend fuels suck for mileage

C25A1guy

Also, what kind of plugs did you change out to?

acn684

Pressures are higher than recommended

Set to 33/31 instead of 32/30. If anything, I should get better mileage like that. I don't want to go higher though as it seems to get "floaty" at one point.

C25A1guy

Delayed double post? LOL

acn684

I'm gonna try to clean out the air filter, but it was washed already during the summer (K&N filter).

ATF was flushed just recently with the O2 sensor changed.

Used the stock NGK 6994 sparks, checked the gaps on all and everything.

Improvement was seen on the whole "cruising part" of driving - highway average was 25-27 after O2 sensor change and went to 27-30 after spark plug change.

However, the acceleration part is killer. In suburban driving, evertime I accelerated from dead it took a huge hit in mpg.

tsxykid105

what type of gas r u using. since its winter the gas companys put more ethonal in the gas so it wont freeze in the tank and thus reducing performance im getting about 22-24mpg and summer avg about 26-30.

acn684

Using 93 from Mobil/Exxon.

Could be the winter mix, but in prior winters I've never gotten as low as 19 average. Even at worst it was 22-23 mpg when I drove the car hard.

I'm barely keeping above 20 and i'm trying to be as light on the accel and avoiding any chances where I need to be back on the brakes again quickly.

heng5

With about 68K, using Mobil One, 5W-30, we can get about 28 mpg, using the AT. During a 2,300 mile trip, using the sportshift the average was 32 mpg. We haven't changed the O2 sensor yet.

Henry

acn684

I'm aware of what the proper MPG should be. Trying to see if anyone knows more about the internals that might be causing this inefficiency.

My current thought is that running rich when the O2 sensor might've clogged something or created too much residue somewhere and that a seafoam flush might help.