Terrible Mpg

Just bought an 05 Ls hatchback automatic for a price that was too good to pass up. anyway had to put $1k worth of parts in the car:
idler pulley, timing belt, serpentine belt, water pump, oil filter, air filter, plug wires, plugs, new radiator, and an oil change.

these are the items related to the powertrain that was replaced. in the car no extra weight other than me (350lbs) the air temp is approx 115 right now i do mostly city driving with the air on i have only filled up once so far to the top and just filled up again my mpg was only 18.2! i have tried to drive differently without seeing much difference. talked to my dad who chged all the parts he said to wait for 2 or 3 fillups since the car had a bad plug wire it drove around on three cyl. So long that it will take the ecu awhile to adjust back to a correct timing. he also said that since it drove so long that the cat maybe plugged and the valves have built up deposits that need to burn off.

what are your thoughts? car has 109500 miles. i would rather sell this and drive my truck since the mileage is not to far off right now. sent from my phone so please excuse the typos.

Give it a couple more tanks. City driving and the Aveo's automatic trans isn't the best combo for high mileage. It is only rated for 23 mpg city in the first place. Combine that with worse than normal traffic and super blasting the A/C (which is known to tank your mileage by 25%) in 115 degree weather makes 18 mpg sound pretty much on the spot.

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Originally Posted by Daox

Give it a couple more tanks. City driving and the Aveo's automatic trans isn't the best combo for high mileage. It is only rated for 23 mpg city in the first place. Combine that with worse than normal traffic and super blasting the A/C (which is known to tank your mileage by 25%) in 115 degree weather makes 18 mpg sound pretty much on the spot.

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at 18mpg I would have to decide if I am going to keep it or not. I have hooked up my scangauge to the car so it can help me figure out the best driving method what I have learned from driving it today is get to 50mph as fast as you can. I get worse mpg driving nice an slow up to 50 then I do taking it up to 4000rpms till I hit 50. So according to the scangauge today I averaged 25.1mpg since my fillup. I have another issue with the scanguage resetting back to default 3.0 liter motor and 15gal tank anyone else have this issue?

on top of it all right now my commute is mostly city in a month or two it will be mostly highway will I see 30mpg on 90% highway driving?

I haven't had that issues with my SG in the Aveo.

I would guess you'll see a huge increase in mileage from going from 90% city to 90% hwy driving.

I consistently get 29 - 33 mpg while using A/C most of the time ... 18 is NOT normal ...

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Originally Posted by bobsemp

I consistently get 29 - 33 mpg while using A/C most of the time ... 18 is NOT normal ...

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yea there was an issue, I had the timing belt changed. There was an issue with something related to it. the timing was jumping around 15 degrees every couple seconds RPMs were jumping at idle that is how I saw the issue. It was changed again yesterday. I have only driven freeway miles since then but was getting 34mpg.

New issue P0402 Eccesive EGR Flow just came on 15 minutes ago. I don't feel like buying a $110 EGR have read it could be related to vacuum issues. In my mind the rpms jumping from 800 to 1150 is also a sign of a vacuum leak anyone else have any ideas about this? The RPM issue is no longer happening after the recent timing belt change. The check engine light it on.

well my memory took a crap between exiting the car and turn the computer on. The code was actually was actually P0420 which is the same cat code that i had when i bought the car so it was even worse than $100 egr it is the $200 cat.

I'd start with a new rear O2 sensor assuming you don't have an exhaust leak at all. Rarely is a P0420 actually a bad CAT.

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)

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Originally Posted by Daox

I'd start with a new rear O2 sensor assuming you don't have an exhaust leak at all. Rarely is a P0420 actually a bad CAT.

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)

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Both o2's were fluxed i think was the term and both came up as in working order. when we looked at the cat the top of it was melted you couldnt see the honeycomb anymore. The car was sputting unburned fuel into the cat for a couple thousand miles while he drove it in 3 cylinders. after we fixed every thing i knew it might come back and it has. this couple also ve causing the low.mpg so i figure its best to change it.

Doh, yeah that'll do it! Hopefully that'll be the last of the fixing up then.

Attachment 5714ok city driving I drive 16 miles to work on SR 200 in Ocala Fl on the right is the mpg it got on 10gallonsAttachment 5715