Getting horrible gas mileage, but mpg gauge normal
 

I ALREADY SEARCHED THIS!

Like the title says, I am noticing my fuel isnt lasting at all anymore but my avg mpg is staying around 30-33 mpg which makes no sense.. ive checked for fuel leaks and my tire pressures and everything is normal. ive also added injector cleaner, new fuel filter, and my fuel pump was replaces about 10000 miles ago because it was leaking. I dont understand why my car is wasting so much gas but its showing 30+ mpg on the screen. Only other variable is that i added lucas oil stabilizer to my oil on the last change but i dont see how that could affect my fuel consumption and i havent gotten any CEL lights.. anyone have any ideas?

Noticed same thing on mi.e

smae thing with mine :( cept im nowhere near 30-33 :lol:

Me to can someone please explain this.

What are you actually getting? It's getting colder your mileage will start to drop

Reset the computer and see what it reads after a day of driving.

maybe is time for new oxygen sensor

Ill try the battery reset.. Yogs, i hope your wrong but i think thats what makes sense to me.. only thing is i dont smell fuel outside/inside the car so i dont think my car is running rich... ill look into it though

You'd have a code for a bad o2. Not always, but usually.
The gas smell is also a good indicator, so I don't think it's that.
It's something to change if all else fails though.

I'll wait on 02 sensors till I put the s256 on. Wont be long now.

But I dont smell gas on stock tune either. Only on when I switch to the performance tune.

is not always smell like gas when a oxygen sensor is bad beside is not too expensive i see it for $44 bucks acdelco on amazon with free shipping

Before jumping to conclusions do your own mileage check.
Fill up and reset the trip meter
Drive a day or two
Fill up again
Write down the gallons of gas that went in
Do the math
Trip meter distance divided by the gallons of gas that went in.

The miles per gallon meter is a average only and varies greatly on how you drive.

The best reading you will get is to reset it on the highway withnthe cruise on and watch it for awhile.

Can also be a thermostat partially stuck open so the vehicle never goes into or takes a long time to go into closed loop. It should set a cel but it doesn't always. You might not have noticed all summer but with the cooler weather the long warm times can have a big affect on mileage.
Watch your engine temp next time you do a cold start. It should come up to operating temp relatively quick this time of the year

I just drove from bogalusa to Tyler tx and it's about 440 miles and burnt a tank and a 1/4 or so. That was stock tune and not going wot cruising at 70.

I remember reading a bulletin a long time ago about SS/SCs having issues with catalytic converters.....maybe you have a clogged cat. It's worth a look; after you drive some highway miles take a look at your cat and see if it's glowing bright red.

Edit: It would also affect power too. Does your car feel like it has the same power?

I'm catless. But its really hilly and was almost 90* the entire trip

So i reset the battery, still same issue. as far as the filling up and counting gallons, the math of what im getting contrasting with the mpg rating on the car doesnt add up. with my mpg being at 33 mpg, i should have gotten 99 miles out of 3 gallons but i only got 80 driving at 70 mph on straight, even road. my catylitic converter is about 10k miles old (got it replaced due to the recall) and when i replaces the cat, i also replaces the spark plugs, fuel filter, and got a new fuel pump (also replaced due to leaking, covered under power train warranty).. only thing that makes sense to me is either a vacuum leak or the o2 sensor. my cel isnt on nor has it been in a long ass time... ill have to scan it and see if theres any surprises hiding.

Same question to you; how does power output feel?

The DIC isn't super accurate over such short distances. Check it vs calculated mpg over a few tanks of gas or possible tank of crappy gas. This is why if you track your mpg every tank you can see when if starts to drop off and compare with what you were getting around the same time a yr ago. Mileage usually doesn't suddenly drop off its a slow drop over months as lazy people don't check tire pressures and dirty filters.

It's getting colder at night so your mpg will start to drop too.

@ mikey851, car still runs strong.. i dont feel it laggy or anything

Hmmm.....I don't know man. I would take a look at your fuel trim etc., like you already mentioned.

So today I finally had access to a scan tool and the code p0171 came up (engine running lean). after looking at the perameters on the scan tool, my uncle and I noticed the upstream (before the cat) o2 sensor was jumping back and forth between 800 mv and down to about 60 mv at idle and the downstream 02 (after the cat) was staying at about 300 mv.. is this normal?

Bump

I have the zzp tune witch they said they eliminated the 02 sensor. What they mean by that? Even if my 02 sensor is bad would it matter since they said I don't need to even have it in dp anymore