WTF, My extreme poor gas mileage is killing me.. Please help

sil_stang02 · Dec 10, 2005

Ok, Here I go with another questions I need help with!!! My 02mustang GT 5 speed that I purchased about a month ago, has been getting EXTREMELY low gas mileage. I just filled the tank back up and did the math, IM gettin 14 MPG, at an average half street and half hwy. Now i now from my other same similar car that I sold, I was getting about 22 to 23 on average.

I mean 14 MPG thats crazy!!!

only mods I have is flowmaster 40 series with no cats. Now, my engine light has been on, because like I said I have no cats and my MILs are on their way here. Could that be the reason im getting poor gas mileage? Ive heard that if the computer senses an error with the cats the car's computer goes into a safe mode, causing fuel / air ratio to be messed up?

Any other advise on any other problems that could be causing that HIGH of a difference on my gas mileage tha I could be checking on while waiting on my MILs?

Please any advised would be appreciated.....

Kilgore Trout · Dec 10, 2005

How many miles are on the car? How often do you go WOT? And yeah, correct the SES light.

sil_stang02 · Dec 10, 2005

Kilgore Trout said:
How many miles are on the car? How often do you go WOT? And yeah, correct the SES light.

The car has 24K on it. I drove like a GRANDMA this last gas tank when i was trying to figure out the gas mileage. PUt it this way, I never even went past 3000 rpm, hell maybe not even 2500 to be exact...

sgarlic · Dec 10, 2005

I get 14 mpg every tank unless it's almost all highway. It's an 04, 7,000 miles. That's not extremely low gas mileage, that's just a tad below average. My advice.. get over it, or get a Honda.

jimfitzgerald · Dec 10, 2005

Get your codes checked. There may be more going on with your engine than just the cats.

jstreet0204 · Dec 10, 2005

Get the ses light read, it could be a bad front o2.

Stangsgrl · Dec 10, 2005

sgarlic said:
I get 14 mpg every tank unless it's almost all highway. It's an 04, 7,000 miles. That's not extremely low gas mileage, that's just a tad below average. My advice.. get over it, or get a Honda.

tad below? W/ my mods i'm still getting 22 on average and i got WOT a few tims on a tank, i do 1/2 hwy & city. '04 w/ 40K miles

yea make sure something else isn't off...since your light is always on u dont' know if something else is wrong.

TacBear · Dec 10, 2005

Stangsgrl said:
tad below? W/ my mods i'm still getting 22 on average and i got WOT a few tims on a tank, i do 1/2 hwy & city. '04 w/ 40K miles

yea make sure something else isn't off...since your light is always on u dont' know if something else is wrong.

I have almost 400 rwhp and I get 21 city and 26 Highway

sil_stang02 · Dec 10, 2005

Ok guys thanks, I just got back from autozone they read my code, they said it was my back o2 sensers where bad(code p1074) i think...

Now do you guys think they are really bad or i got the code because i dont have MIL eliminators and no cats? They told me in autozone that without cats the o2 sensors will go bad really quick and I will have to buy new 02 sensors no matter what!!!! And they also said that was my reason for bad gas mileage and that mil eliminators will not fix that (only the engine light), I will still get bad gas mileage unless I get cats put on.

And if I go ahead and install mil elim would it even matter if the 02 sensors are gone bad or not?

what do you think i should do?

jimfitzgerald · Dec 10, 2005

sil_stang02 said:
Ok guys thanks, I just got back from autozone they read my code, they said it was my back o2 sensers where bad(code p1074) i think...

Now do you guys think they are really bad or i got the code because i dont have MIL eliminators and no cats? They told me in autozone that without cats the o2 sensors will go bad really quick and I will have to buy new 02 sensors no matter what!!!! And they also said that was my reason for bad gas mileage and that mil eliminators will not fix that (only the engine light), I will still get bad gas mileage unless I get cats put on.

And if I go ahead and install mil elim would it even matter if the 02 sensors are gone bad or not?

what do you think i should do?

Get you MIL eliminators installed. The rear O2 sensors don't matter.

Kilgore Trout · Dec 10, 2005

One time I told an AutoZone guy that I needed some ATF to put in my power steering resevior. He laughed at me and said; "son power steering fluid goes in there". I said you are incorrect... He called out all the other AutoZone genuises and they all agreed that I was crazy

Moral of the story, go ahead and listen to them, and then run their "advice" by StangNet...

Justin03GT · Dec 10, 2005

i average 15-16mpg 98% is city driving with a fairly heavy foot...gets as high as 28 on trips to MD going up 95..

sgarlic · Dec 10, 2005

Stangsgrl said:
tad below? W/ my mods i'm still getting 22 on average and i got WOT a few tims on a tank, i do 1/2 hwy & city. '04 w/ 40K miles

yea make sure something else isn't off...since your light is always on u dont' know if something else is wrong.

Yeah, I said unless it's almost all highway (which would imply mainly city driving.) I believe 22mpg average if you do half highway and half city.. definately.

What is city driving for you? For me, it's driving one mile to work and back every day, then occasionally sitting in stop and go traffic for an hour or more just trying to get to the grocery store. Where he lives may be the same. A city drive for one person may be a completely different set of circumstances.

sil_stang02 · Dec 10, 2005

jimfitzgerald said:
Get you MIL eliminators installed. The rear O2 sensors don't matter.

Sounds good. so with the mil elim the air / fuel ratio should go back to normal as if I had cats and good 02 sensors, EVEN IF I DONT??

thanks

Stangsgrl · Dec 10, 2005

sgarlic said:
Yeah, I said unless it's almost all highway (which would imply mainly city driving.) I believe 22mpg average if you do half highway and half city.. definately.

What is city driving for you? For me, it's driving one mile to work and back every day, then occasionally sitting in stop and go traffic for an hour or more just trying to get to the grocery store. Where he lives may be the same. A city drive for one person may be a completely different set of circumstances.

true about the city driving. I drive about 10-15 minutes one way to work in "city" traffic then 25-30 minutes on the highway. Most of my errands and other driving is on back roads & cities with traffic lights hardly ever in 5th. So really my driving is pretty close to 1/2 & 1/2, city/highway.

jstreet0204 · Dec 10, 2005

sil_stang02 said:
Sounds good. so with the mil elim the air / fuel ratio should go back to normal as if I had cats and good 02 sensors, EVEN IF I DONT??

thanks

No, rear o2's only serve one purpose. To test for cats. They won't effect performance, or closed loop a/f ratio. And before anyone chimes in with, they won't cause the car to run in limp mode either. You should start looking for other causes for the bad mileage. Sticking calipers, low tire pressure, air filter, plugs, etc. You might also want to test the front o2's with a volt meter. They can start to get lazy long before they ever throw a light.

sgarlic · Dec 10, 2005

jstreet0204 said:
No, rear o2's only serve one purpose. To test for cats. They won't effect performance, or closed loop a/f ratio. And before anyone chimes in with, they won't cause the car to run in limp mode either.

Good post. Regardless of how many times we tell people, post links, post quotes from the service manuals, etc.. somebody always refuses to believe they are called "Catalyst Monitors" for the simple fact that they monitor the catalyst system.

Stang|ess · Dec 10, 2005

Rear o2 sensors don't affect a/f ratio, performance, or anything other than to light up your cel. They monitor your cats, and if you were to get mils installed, the cel would go away.

Are you running rich? Did you do a tuneup? I'm getting 15.6ish with about 80% in mild/moderate traffic, and 20% highway. Ac on about 80% of the time and I usually leave it in 4th because I don't want to hear my exhaust leak in 5th

sil_stang02 · Dec 10, 2005

jstreet0204 said:
No, rear o2's only serve one purpose. To test for cats. They won't effect performance, or closed loop a/f ratio. And before anyone chimes in with, they won't cause the car to run in limp mode either. You should start looking for other causes for the bad mileage. Sticking calipers, low tire pressure, air filter, plugs, etc. You might also want to test the front o2's with a volt meter. They can start to get lazy long before they ever throw a light.

ok man thanks, just that so many people are telling me different things. Im going to go ahead and install those mils for the engine light. And go back to autozone afterwards to see if it throws another code. Its just frustrating because its so much different in EPA. Im wasting so much gas!!!

anything else it could be other than the front O2 sensors, plugs, fuel filter, sticking calipers???

Oh, how do i test the sensors??

thanks
thanks

Kilgore Trout · Dec 10, 2005

Clogged fuel filter will adversely affect mileage. 24k is getting close to the 30k replace interval. Worth a shot...

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