Stock 03 Mustang Gt Getting Awful Gas Mileage. Help!

silvergtcoupe03

New Member
May 25, 2012
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Ok, this is going to be a bit of a long story but if you could help someone in desperate need that would be a huge help

I bought this car about 4 months ago and when i bought it, it was great and i loved driving it, and i still do. About 2 months after i bought the car, I got rear ended by some kid in his corolla. I finally got it about a month later after it being delayed for being ready for repairs for parts coming in late and 2 bad axles being sent in to them. When i got it back about a month and a half ago and went to fill it up, i noticed that my mileage was about 5 mpg less than what i used to normally get around town which was about 17 or 16 mpg even when not being nice to the car. it got 12 mpg on that fill up and a few fill ups later it got 15.6 mpg which was strange because it usually got awful mileage and i also got 15.2 one other time a few fill ups ago. i drove it on the highway about a week or two ago and got about 22 mpg on the highway with cruise control at about 60 mph. Now in town i get about 10 mpg and it's really hard for me because its getting expensive for me to drive it and i love driving my mustang. Nothing seems wrong with my car so far besides some squeaking in the rear wheels but i doubt that would have anything to do with getting 5mpg less than usual. Only mechanical or functional parts on the car that were replaced or fixed was the right exhaust pipe and the rear axle. Car can feel down on power at times but its usually from using the a/c. Only fill up at Phillips 66 (Conoco-Phillips), Mobil, or BP stations.

Sorry this is a lot of reading but if someone could give the time to read this and help me solve this problem I would greatly appreciate it.
 
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Can you give a better explanation on the damage? I see "2 bad axles" and "some squeaking in the rear wheels". My guess would be that there was a lot more damage than you thought. Damage to the axles along with a squeaking sound from the rear could mean that the rear is misaligned, or that there is frame damage.
 
Squeaking in the rear wheels suggests that the brakes might be dragging. Put the car in neutral on flat ground: How hard is it to push the car?

After you drive for a while and coast to a stop, how hot are the rear wheel hubs?
 
Greenstang - I had an idea it could be that, my check engine light is not on but i have heard of situations where the computer won't throw a code. The car sometimes will take a few more seconds than needed to start up, i doubt its my starter because its not clicking and its not my battery because its not slow cranks, i think it could be a fuel pump or filter but idk.

Nightfire - Yeah sorry for just a brief explanation, 2 axles that the repair shop were bad, the first one they put it on and test drove it and made a weird vibrating noise so they ordered a new one, the next one they ordered they could visually see that the one they bought was bent, and the third one they bought was good so thats the one i have now, the axle feels fine and it drives pretty normal, and when they observed the damage, they said that the guy who hit me had just missed the frame so no frame damage, and the wheels were squeaking before the accident but they've been squeaking a bit more now, i think they gave me the same rotors i had on my old axle. The steering column was about an inch or inch and a half offset when he hit me so do you think it could have offset something? I'm not that mechanically inclined with this stuff but i can tell there is something wrong.

Trinity - i have put the car in neutral down a hill and i don't feel much or even any drag at all, it doesn't lose speed as if the brakes were dragging, and the hubs don't feel really hot when the car's stopped.
 
My Mustang would use to take a while to start right after it was driven and the motor was warm.... Does yours do this too or does it do it all the time?

If it does it when its warm I have found that this is one of those annoying nuances of owning a 4.6 . I suggest you do a full tune up, plugs, fuel pump, air filter, sea foam in the vaccum line and some in the gas tank. Only use MOTORCRAFT plugs, getting hotter platinum plugs are not worth it because I ran some and the car ran like poo and have found on the forums that these cars when mostly stock like the motorcraft plugs.. Hope that helps you out, btw how many miles are on your car?
 
Trueblue - Yes, thats exactly what happens, it doesn't do that all the time but in my friends driveway one time it had a hard time starting up even when i was pressing the gas pedal a few times. My car has about 103k miles on it, it just started getting bad gas mileage after this accident, but idk what it could be, it did it a few times before the accident too. Btw, i bought it from a dealership about a few months ago and they did a lot of work to it so i doubt the plugs or anything would have gone bad within that amount of time.
 
trueblue - also, i read on the internet and about 1/2 of the people who use sea foam have had leaks or problems with pressure, but do you think the fuel pump being worked with would help it? because around where i was hit looks like where the fuel pump is, but my friend had a fuel pump go out on a 92 chevy 1500 and it wouldn't even stay running, it would start up and then almost immediately die so i don't know if the fuel pump could be bad if its still working, because the car still revs and runs fine, its very strange and i can't seem to figure out what the problem could be.
 
I would still go ahead and pull the plugs to inspect them, if they are worn out it will be fairly obvious. The plugs should look tan and have no oil or residue on them. Also are you running 5-w20 oil? If you aren't then I would switch to 5w20 because that helps our cars get better gas mileage. I think you fuel pump is fine because the car would not run properly if it wasn't. For the seafoam I haven't seen anything bad about it on this forum and its one of the reasons I did it to my car. When I used a can of seafoam I put 2/3 of the can through the vacuum line and the car is running fine with no leaks. It really helped my car out in throttle response and gas mileage area.

Just doing all the basic tune up will help because you know its all new, and if none of that helps you get better mileage it will give the guys on here some more help in helping you.

Good luck and welcome to Stangnet.
 
i would look at the plugs but i don't know the gap for the plugs and i don't want to mess that up, and I'm pretty sure I'm running 5w20 because i doubt the auto body shop would have changed the oil in it, and yeah i have sea foam at home I'm using it on a little honda bike and its working great so i'll put some of that in it. My friend's dad can probably help me too since he rebuilt his 1989 ford f350 and its pretty much fully restored and looks amazing. If he can't figure out the problem i'll probably take it to a dealer. Thanks for your help anyway.
 
The plugs are pre gapped so you don't have to do anything to them unless you tamper with them. I really believe that doing the tune up will help you with your mileage issue. Because you are only getting 1.5 mpg less than what Ford said the car would get when it was brand new..
 
i doubt your gas mileage issue is related to your damage from the wreck unless the rear brakes are dragging. The FPRS can cause bad gas mileage so can about 50 other things. you might have to do some more digging and post some more info. start with what was suggested above ( fuel filter, plugs auto lites or motorcrafts, oil change, and maybe trans and rear end fluid) atleast do the plugs. wait until the car has cooled all the way and be extra super very careful not to over tighten when putting the new plugs in they strip easy. maybe do alittle research before doing the plugs, read some post about stripped plug threads just so you know what to do and what not to do.

the only reason i suggest the FRSP is because of the hard starting when warm. common on these cars when the first sighs of a failing FRPS but there are also other things that have similar symptoms. most are fuel related. start with the plugs.