Bad gas mileage

Raspo93 · Aug 25, 2011

I have a 2002 Mustang gt that gets about 10mpg and i cant seem to figure it out, I have done a tune up, plugs wires and brakes. Didnt really help the mileage at all. I dont think i drive the car harder than anyone else who gets decent gas mileage so i dont think that is a problem. I dont know what i should try next.

bhuff30 · Aug 25, 2011

Does the car have different gears? That would affect the odometer readings. what kind of driving do you do city/highway? Any codes or CEL? Do you smell gas around the car (leak)?

10mpg is pretty bad. In town, I generally get around 17-18mpg, and pure highway, 24-26mpg. It sounds

Lugnuts · Aug 25, 2011

+1 on the possibility of a leak. When the car runs, does the exhaust seem normal or does it smell rich and burn your eyes bad?
Is the car stock or modified? 10mpg is not bad if you are making 1500hp!
Give us some more info.
Thanks.

trinity_gt · Aug 25, 2011

Raspo93 said:
I have a 2002 Mustang gt that gets about 10mpg and i cant seem to figure it out, I have done a tune up, plugs wires and brakes. Didnt really help the mileage at all. I dont think i drive the car harder than anyone else who gets decent gas mileage so i dont think that is a problem. I dont know what i should try next.

Which wires? The 02 has COP and no plug wires per se (at least not serviceable ones...)

wmburns · Aug 25, 2011

How many miles?

Did the tune-up include new O2 sensors?

Did the tune-up include cleaning the MAF?

Are there any DTC codes?

Are there any exhaust or vacuum leaks?

+1 on the gear ratio. Very good point! If the odometer reads low, this will make the gas mileage appear worse than it really is.

+1 on the gas leak theory. It's a common problem for the gas tank filler neck grommet to dry and crack. It's easy to see that gas spilling out of the tank while driving will decrease mileage.

N8Dogg98 · Aug 25, 2011

The problem with the gear ratio though is he would have to have a taller than stock gear ratio in there. I don't know anyone who has gone from 3.27's to 3.08's for example.

Jhunter · Aug 25, 2011

Really need a full breakdown on the car. What mods? Has a tune been downloaded that could be off? Are you riding with the park brake on? Has any work been done to the transmission? If it's an automatic is the car shifting to overdrive? Do you drag race from one light to the other? Etc. Etc.

Raspo93 · Aug 25, 2011

The car has 46,000 miles, all stock except for cut outs welded on after the cats on the h pipe. i cleaned the MAF a while ago randomly at a friends house because he had the spray for it. I didnt change the o2 sensors, i was thinking about getting a O/R x pipe to get rid of the cats if that could be a problem. The guy i bought it from said it was 100% stock when i bought it so as far as i know it has stock gears. There are no lights on the dash, its a manual. Also, when its full throttle it will smell like rotten eggs, idk if that would have something to do with it

wmburns · Aug 25, 2011

Raspo93 said:
Also, when its full throttle it will smell like rotten eggs, idk if that would have something to do with it

Have the cats been gutted? If so, likely that is what the smell is coming from.

For all I know, it could be the cutouts. There is a reason exhaust is usually run all the way to the bumper.

Are you sure the check engine light actually works? It should come on during the lamp test.

Has the gas mileage always been bad?

Consider having the fuel injectors cleaned and flow tested. Injectorrx.com has done well by me.

Do you trust the PO? Seems likely that the car is stock but the tune is not.

Regardless, the best reasonable course of action is to start from a known good tune up.

03_TrueBlue_GT · Aug 26, 2011

All of these are good questions but I have a few. Does the car have aftermarket rims on it like 18+? What kind of spark plugs are in the car? Whats your tire pressure at? how has the weather been where you are at? Is it really hot like hotter than normal? Are you using synthetic oil?

Thats all I can think of...

Stumbaugh · Aug 26, 2011

wmburns said:
There is a reason exhaust is usually run all the way to the bumper.

Not having tailpipes on the car will not effect fuel mileage. I had dumps on mine for a long time and just recently put tailpipes on it (tired of the drone) and fuel mileage stayed the same.

Stumbaugh · Aug 26, 2011

OP,

Change the fuel filter, and run some lucas fuel treatment thru it.

Lugnuts · Aug 26, 2011

The smell of rotten eggs you mentioned would lead me to worry about the function of your cats. When backed up they typically smell of sulfur (rotten eggs).

Stumbaugh · Aug 26, 2011

Lugnuts said:
The smell of rotten eggs you mentioned would lead me to worry about the function of your cats. When backed up they typically smell of sulfur (rotten eggs).

This is true. I talked to my exhaust guy a minute ago and he said the same thing. He said that the cats are stopped up.

Raspo93 · Aug 26, 2011

Well im putting a O/R x on it so maybe that will help

wmburns · Aug 26, 2011

Raspo93 said:
Well im putting a O/R x on it so maybe that will help

Almost double the gas mileage by installing a new catback exhaust system? Suggest documenting this as it would make a great ad. The exhaust makers will be all over you.

"Much to learn, you still have."
―Yoda to Dooku

03_TrueBlue_GT · Aug 26, 2011

wmburns said:
Almost double the gas mileage by installing a new exhaust system. Suggest document this as it would make a great ad. The exhaust makers will be all over you.

"Much to learn, you still have."
―Yoda to Dooku

Haha true that, although I lost some mpgs after I installed my o/r x, but its probably the sound I love so I dont drive as conservatively as I used to lol...

Raspo93 · Aug 28, 2011

03_TrueBlue_GT said:
Haha true that, although I lost some mpgs after I installed my o/r x, but its probably the sound I love so I dont drive as conservatively as I used to lol...

Im doing the same exhaust set up as you o/r x with flowmasters

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