General Maintenance & Repairs - killed my mpg

so i bought a 02 z m6 from a dealer a couple months back they replaced a cat that was bad. it had some no name catback that was horrible on it so i put on a pipe after the y with a race bullet dumped before the axle. my cel came on even after the new cat and now with my setup i get 200 miles to a tank. car also has slp lid with kn filter and ram air mod. o yea and the 02 sensors are new as well.


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And? You bought a ten year old v8 muscle car not a Prius.

The 200 to the tank is about right

The 200 to the tank is about right

200 is regular? i normally get 240ish mixed city/hwy all highway i get 320 ish
whats your driving style like?
what code is it throwing?

if your complaining about it now, don't do h/c/i lol you don't by these cars for mpg, you buy them for the "WHOLY SHIT" FACTOR" haha

those comments about that being normal are completely whack something is wrong with your car or you dog it every where you go my 02 gets about 350 mi/tank on the highway with the cruise set at 75 ish start with cleaning your maf sensor

When I had my 01 ss I had a heavy foot and got shitty mileage but I knew it was driver related. If op has heavy foot then yes he will get 240ish. If he doesn't then I'd recommend cleaning the maf and changing the fuel filter first

I get about 240ish to the tank for normal mixed city/highway driving. On long trips I can squeeze 300 of out it all highway.

im not by any means complaining about getting shitty mileage in a v8. it was the point that with the shitty catback i was getting the normal 240 to 280 ish then i put the dump on and it went to shit. ill do as stated above though with maf and fuel filter


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I know after doing full exhaust on my car I got on it a lot more than I did before. But 200 miles to a tank is still not too good.

I did get on it a little more often but lately i just cruise and its a 30 mile round trip everyday to work and back. with only about two miles in town.

Math tells me I should be getting 336+ miles per tank (assuming 20mpg which is lower than I actually get) with spirited driving, running rich, CEL on (no tune), and 2.73 gears.

I usually fill it up before it hits a quarter tank though, never run it to E

i normal got around 18-19 mpg in my firebird. a corvette with the same driving style should get better than that.

try a oiless air filter and clean the MAF.use a hand held scanner and check the fuel trims and check the O2 .

Have you verified what the code is that is being thrown? There could be something else wrong with it.

i will prob end up going to a oil less air filter and i havent took it in yet for codes since isnt there the two cats from the manis then another one after the Y cause if so i only have the two. so i figured the deleted third cat would throw codes. if i unplug the pcm fuses to reset im ok until i punch it then the CEL light comes on.


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For starters, don't base your mileage on miles per tank. Top the tank off, run down, top off, divide miles driven by gallons to return to topped off. That being said, my M6 averages 28 mpg on road trips @ 80 mph. City driving is right at 18 mpg of easy driving, around 14 mpg if I dog it around town.

If your driving habits are EXACTLY the same, I would look into the issues others have suggested. But I noticed just a little spirited driving wrecks my mpg.

200 is regular? i normally get 240ish mixed city/hwy all highway i get 320 ish

This sounds about right for me as well.

Have you verified what the code is that is being thrown? There could be something else wrong with it.Do this or you're groping in the dark. I think Autozone (outside of CA) will read codes. Do your best to find out what's wrong and go from there.

cleaned the maf sensor today. was pretty surprised how much black shit was on there but now its good as new and my ses light is off. this coming weekend im still going to do the fuel filter though


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Have you scanned the car for codes Yet? What exactly is the code?

so i bought a 02 z m6 from a dealer a couple months back they replaced a cat that was bad. it had some no name catback that was horrible on it so i put on a pipe after the y with a race bullet dumped before the axle. my cel came on even after the new cat and now with my setup i get 200 miles to a tank. car also has slp lid with kn filter and ram air mod. o yea and the 02 sensors are new as well.


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You need to have it scanned to see what code comes up. If they put an aftermarket cat on it you may still get a P0430 cat efficiency code as most non factory cats do not have the same amount of the precious metals inside that make them work as efficient as the factory piece does. Walker direct fit cats usually do good at keeping the P0430 from resetting but I know people that had a "universal' cat installed & didnt get the light out.

The 200 to the tank is about right

That mostly depends on your driving style but a stock M6 is capable of well over 300-350 miles to a tank. I got over 250 out of a tank a few weeks ago mods in sig. mostly highway driving.

I'm sitting on 180-190 a tank all city in my A4. No AC widows down 100% or the time. I get 180 no matter what baby it or racing check Gages comes on around 180

I have a bone stock 01 TA with a hooker muffler and no cats. It has a minor tune from having a 6 speed transplanted in it and the rear 02s shut off as well as some odds and ends for emissions deletion. I averaged 28mpg with the A/C going 75% of the time and my 3.73 gears on a recent 1000 mile road trip. It was put-put driving mixed with some street racing but in all it averages out pretty well. My understanding is that having a CEL will throw off your gas mileage a bit. My car has 202k on the odo but I seafoam it every 2 months or so to keep it flowing smoothly. I never change the fuel filter but I emptied it out once and got clean clear gas out of it. That seafoam is some awesome shit. Hope my advice helps you out.

I'm pushing 400hp and still getting 29 hwy and 17 city, wot runs wreck me though and overall jacrabbit launches.