I'm GMS1, stock pipes and a K&N intake, and I'm averaging about 25 mixed highway/town driving, which is decent - I can hit 32 highway if I can ignore the urge to move faster.

I think Vince is applying some stone age thought to the modern exhaust question. Reducing exhaust back pressure = increased gas mileage in almost every circumstance, unless you're talking about a car with a ragged cam. I cannot imagine a direct-injection engine on stock cam timing, which controls fuel pulse timing as well as width, suffering any adverse effect from reduced back pressure - let alone a turbo'ed one, which sees a fairly fixed back pressure regardless, considering there's a big-old obstruction called THE TURBO that is the principal cause! Everything after the turbo only serves to spit out the exhaust gas in the proper direction; unless there's somebody who can tell me why it would be otherwise, post-turbo pipe diameter matters very little (unless its too small or choked), since there's nothing meaningful gained by attempting to change exhaust flow past both a primary restriction like a turbo, AND that you have no scavenging. A 3" cat-back should only change the resonance.

If we're talking about my '80 small block, stuff would be different, since I can easily over-scavenge out of my Pacesetters, and draw fuel mix straight out of the cylinders with would could be described as a 'too-efficient' exhaust system.

Do you still have your cat on the dp? Changing how the O2 sensor reads after changing to an aftermarket cat - or deleting one - can affect mpg.

 

I need to clean my air filter but i'm getting 17 city

 

The rear o2 sensor should have jack **** to do with AFR or MPG. It usually serves only to detect and report to the ECU whether the cat is functioning properly.

OP, I thought you took the car back after you made that thread about the mods/tune you were unaware of. Did you atleast figure out what tune is on it?

 

no just dp k&n drop in and muffler delete sc tune.

 

What are your tires like? Tires play a good part in MPG.

 

the worst ive ever seen is 27 MPG... i average a consistent 31-33 when driving spirited.. the highest i saw was back when it was warmer in november and that was 38 MPG.. i wanna see 40+ yet


either way.. base models represent!!

 

Is that the 2.2 you're talking about in base models? Had the older version 2.2 ecotec in my 02 sunfire, great motor never once a problem through 250,000km and always great mpg even after supercharger was put on it.

 

I have never even gotten 30 no matter how easy I drove the car even before the tune, so I am very skeptical of these claims.

 

Same here. I get the same mileage before and after the tune.

 

I can most definitely confirm the 30-plus mpg. When I first got mine (09 TC sedan), I was way off on my shift points (thanks to driving my 95 Z28 six-speed). I shifted low, and practically lugged the car most times. I also was running a commute with nearly flat 40 mph roads, and fairly open highway thanks to my early, early morning commute. With no stoplights, traffic or other crap to interfere, and with me being completely off-boost most times, I was hitting 32 mpg.

Now that I'm buzzing it higher and keeping it in the power zone, I'm easily 6-8 mpg lower, if not more some weeks, when people annoy me!

 

Yeah I would believe it at those speeds and conditions. Just not at 70-80.

 

I never updated the old thread. I put a question out in the regional forum looking for the original owner, and he found me. We PM'd back and forth, and he says he never tuned it. He satisfied my questions and would have nothing to gain or lose by lying to me so I took his word for it. The car was in otherwise immaculate shape, but I originally took it back because I could not verify if it was tuned or not.

The dealership I bought it from took it (after I returned it) to a chevy dealership for a lookover, something they had not done previously, and that dealership gave it a thumbs up. In the mean time I have done a TON of reading on here, and while I dont know yet why my boost spikes to 25 psi when its floored above 3200 rpm's, I have a feeling it might be a mechanical issue.

I am having Vince tune for the bolt ons on the stock tune, so I hope that resolves my issues and sees the MPG's come up. Its kind of funny to me that I am about to do the same thing that I was worried about prior to purchasing, but I think that was partly due to not knowing how the car was treated for its first 28K miles, and partly due to worry of inheriting an HP Tuners hack job. The spike boosting and CEL I got the first time I took the car home I am thinking was a mechanical issue. Possibly having to do with the BPV? I dont know. But my big concern was if there was a crazy tune causing it to spike 25+ and since both the original owner and the other dealership were able to confirm no tune, I felt good taking the car home. I am sure that is WAY more than you wanted to know.

 

There's nothing in it for me or the people who say 30+ mpg is possible if it's not. It could be your mods/tune if you have any or old filters/plugs. It could also be the length of trips you go on. you need hwy only or at least 60%-70% hwy miles to see 30 mpg or more. the 30 mpg EPA rating is for hwy only so according to EPA you need 100% hwy miles to hit even 30 mpg, let alone above 30.

 

yep the good ole 2.2. reliable as hell like most ecotecs and good mpg's all around for the most part

 

If the GM Tec II can verify the tune is original then I guess I'd be inclined to believe them Did you check your vacuum lines going to the diverter valve and bypass valves? How about the maf sensor and map sensors? What code was it showing?

 

There were two codes, one with the MAP sensor, and one for engine overboost. I messed with all of the hoses and lines I could see, everything seemed tight. Not really sure what else to do really. I really wish I knew more about turbo cars.

 

This past year my car has pretty much only been used to drive me to work and back. Until about 4 months ago it was 24 miles round trip and 90% of that was highway. I would avg 30-33mpg if I didn't get on it at all and about 28mpg if I did. Now I am only running 10 miles round trip to work and its 90% city. I get between 23-25mpg, but feel I could get more if I wasn't in such a hurry every day and I didn't have a busted lifter. I have noticed that when I don't use the cruise I can get better mpg. When I am driving on the highway I always coast as far as I can in 5th gear before hitting the brakes. This makes the biggest difference when exiting on long ramps. In the city I will leave it in 5th and break as late as can. When i get below 40mph I will take it out of gear and keep it in neutral until fully stopped. As most of you know this engine cuts all fuel when you let off the gas in 5th gear and doesn't start to add fuel until just under 40mph or you hit the gas. Once I get my geo metro done none of this will matter and I will put the cobalt on e or something the pump doesn't offer.

 

your turbo cuases enough back pressure that your exhaust shouldnt make a difference being that its 3 inch