bad mpgs

[akcamaro02]

for a while now, i've been getting real bad gas mileage..usually 13-15 mpg..i don't get on it, i've just been driving around normal..it's all city miles. but the air filters new, recently changed oil(maxlife synthetic), fuel injector cleaner used every oil change, seafoam used every 6 months, tires are new and inflated. everythings good but i just don't understand how i always get so bad of gas mileage.
the only thing i have noticed is that i replaced the i pipe w/2.5" piping and the over the axle pipe with 2.5" piping, replaced the muffler with a dynomax super turbo muffler and have dual exit and since then, it went from about 16 mpg to about 13-15 where it is now. when i first bought the car almost two years ago, everything needed to be replaced but somehow it got 20 mpgs, as i replaced things, it gradually got worse towhere it is now.
anyone have an idea?

[Bandit127]

Re: bad mpgs

First: Take your car to a shop and get a injector service done, the store bought injector cleaners are worthless.
Second: The exhaust wont do that, unless its plugged, but then you'd experience lack of power and possibly a high pitch screeching noise from escaping gases.
Third: Replace your fuel filter, it doesnt sound like you've done that yet.

[akcamaro02]

Re: bad mpgs

i had the fuel filter replaced when the fuel pump went out..october 2008.

[truekoa]

Re: bad mpgs

you carrying around a bunch of stuff?

Also, seafoam every 6 months? isn't that alot?

[akcamaro02]

Re: bad mpgs

nope, just a broken antenna in my trunk and my bookbag.
and i was told twice a year. i only add it to my oil before an oil change. i have never done the brake booster method..all it does it cleans carbon..i accidently put it in after an oil change once and over 3 months, it caused my motor to burn about 1 qt of oil, and i did see a decline in gas mileage during that oil change however, that's been a long time and i haven't had a tank with over 18mpg in over a year.

[bwkmaro]

Re: bad mpgs

what kind of parts did you use when you did a tune up? because if you use anything but the best pretty much your mpg will suffer i get 23-25mpg hard on it do a tune up, idiridum plugs, acdelco coils and sum msd 8.5mm wires. youll get 20 or more again unless you used good stuff to do the tune up with then its deeper. i got 2 more mpg going from bocsh platinum plugs to ngk idiridums

[akcamaro02]

Re: bad mpgs

i have never done a tune up..cars only got 84k on it. should i do one at that mileage?

[ssms5411]

Re: bad mpgs

I wouldn't seafoam your car that often since all the carbon will get burnt up but it also puts that carbon crap on your spark plugs. So I would check your spark plugs , for build up and to see if your running rich. Or just replace them while your at it for $15 with NGK TR55's and borrow a scanner to see how your O2 sensors are running. Since you have larger exhaust the car might be pulling more fuel since stock cars are set way to rich from the factory anyways. So maybe a PCMforless pcm with your currrent mods might make a good differnece, since they can adjust your A/F ratio. Some have said stock A/F ratios are like in the 11's at WOT , which it should be 13.0 and 14.7 at idle around there. A partially bad cat could be starting to develop also , I would borrow a scanner if you don't have one and check everything out, O2 senors you can get for $40 a pop from www.getgmparts.com Delphi's which are good. So I would do plugs, O2's and like someone suggested some good wires like MSD 8.5's or even 8mm wires. Good luck. With my mods and running 65lb injectors I still get 25-26 MPG's that mostly city 25-45 mph and some highway 50-60 + mph.

[Blizzard242]

Re: bad mpgs

replace your o2 sensors. Those are a huge factor in fueling.

Oh, Hi steve.

[ssms5411]

Re: bad mpgs

replace your o2 sensors. Those are a huge factor in fueling.

Oh, Hi steve.

Hello Blizz. I think I explained the O2's in my post. LOL

[akcamaro02]

Re: bad mpgs

thanks for the advice. i'll try one thing at a time and see how it goes, then i'll actually know what it is.
anyone got a preference on spark plugs? i hear bosch platinums are good, my friend put them in his silverado.
i found some msd plug wires
also...would i have to buy something to measure the gap in the spark plugs?

[Choppers]

Re: bad mpgs

Stay away from the Bosch. Many here prefer NGK tr6's. The last time I did it I put in Autolites because I was dead broke and thats what was in it already. But I would if you have the money put in NGK tr6's.

[Blizzard242]

Re: bad mpgs

Hello Blizz. I think I explained the O2's in my post. LOL

Yeah, I only saw your post come up after I had posted.

Hence the, "oh, hi steve"

[akcamaro02]

Re: bad mpgs

do i need a gapping tool or something when i put the new spark plugs in?

[bigairboarder44]

Re: bad mpgs

you should definitely have one handy because it's very unlikely that the plugs are gapped correctly out of the box. the gap should be .06" +/- .02"