92SilverSHO

iTrader: (3)

Ok this is the quick story, bought the car with 34,500, on it, changed all the fluids, new plugs, msd wires, mobil 1. i was getting 15mpg around town and 32mpg on the highway. I move to CANADA, first tank of Canadien Gas, my car started getting about 13mpg, then next fill up, 11mpg, then i threw an SES light, it was a bad cat, so i got that replaced, now im getting the worse gas mileage ever!! im at 37miles on 4 gallons of gas! 94 octane. To me, the only thing changed is the gas, i always put sunoco 93 and the car liked that, this crap, mileage wise you can see. Even though there is more stop and go up here in Montreal, i NEVER get on the car due to traffic, i granny shift at 1900 rpm then shift and im easy on the throttle and i pull 9mpg!! how the hell can my car be that inefficient. She has 42000 miles and i have a fuel filter as the only thing i havent replaced, but i seriously doubt thats the problem, since some people replaced that for the first time well beyond 50,000 miles and notice no difference. Im out of options what to do, im pretty frustrated. I just want my 15mpg back, this is crazy! at 3.40 cents US for a gallon of gas, i cant afford it to be this bad on gas.

TheBlurLS1

iTrader: (8)

o2 sensor?? MAF sensor? sounds like you have a problem with somthing thats determining how much fuel it should dump. have you smelled your exhaust while it was idling latley? with that problem with your cat, its might be related to your o2 sensor. just my .02

jaberwaki

well to start cats dont just go bad.
they are a tell tale of something else wronge.
water in gas can cause the simptom you are seeing...
there is something you can buy at local parts store called dry gas, if you put it in and it fixes you up(it will take 20-30 miles to really work) then go back to the gas station and punch the owner in the mouth...

TheBlurLS1

iTrader: (8)

you might want to run that dude down to the fumes, then put gas it in somewhere you've never gotten it before when your on the brink of running out.

VIP1

Things to check:
O2 sensors (there are four at about $50 each, I think)
MAF Sensor
Fuel Filter
Air Filter
Damaged intake inlet (hose before and after MAF -- especialy if any sputtering/surging)
CATs (they can plug up with age, but not at 42K miles, more like 100-200K miles)
Bad Fuel
Spark plugs & wires

Get the computer scanned for any stored codes. If you know anyone with logging software, have an average drive logged and look for anything unusual.

Check the air filter and look into the intake tract.

The next cheapest and easiest is to let the tank go near empty and fill it up with a good name brand gas from a place other than you have been using. I always use Mobil.

Next would be to replace the O2 sensors and/or spark plugs and wires.

If you are still haveing issues, you can go onto the more expensive items on the list.

92SilverSHO

iTrader: (3)

Well, i just replaced both o2 sensors 4k miles ago, both fronts. And we did hook up autotap, everything seemed fine except the Cat low efficiency code. I wish i could fill up with better gas, but ive tried 2 different Canadien gas stations, ultramar and Petro Canada and there wasnt a noticeable diff in gas mileage. Also its 91 octane for Ultramar, only petro canada sells 94 octane. No diff for either octane for gas mileage.

TheBlurLS1

iTrader: (8)

do you have a big rear end (4.10 or somthing)?? is your speedometer correct?? if not, then you could just be getting a faulty mileage reading.

if you havent had any changes made that would affect the speedo, id change the MAF. do you have a buddy with an ls1 f-body? maby you could swap for a while or somthing.

92SilverSHO

iTrader: (3)

well, the car doesnt stumble or smell of gas, but it sure as hell its eat now. My car always burned about 3/4 of a quart of oil every 1k miles, but i was still getting better gas mileage than i am now. The car hasnt thrown any other codes.

onehardmaro

Unless the converter was a lemon something had to ruin it. A bad cat isnt going to give bad gas mileage either. Replace both front o2's and check for exhaust leaks around the cat that was replaced. I would check for an exhaust leak first. That would bring in cold air tell the o2 your running lean and pump more fuel to compensate.

VIP1

You engine also seems a bit oil-hungry. Has the oil consumption increased?

jaberwaki

do you have some place you can get it on a wide band ?

92SilverSHO

iTrader: (3)

well not here in Montreal. I just really dont get it, im pretty mad, considering gas prices here suck, and my car is getting worse gas mileage than cars having 2-3 times my power with no obvious problems except drinking the gas!! ehh i hate this, i wish it would tell me whats wrong instead of guessing!