Overall Gas Mileage on my Stock 2001 GT is Horrible. I Don't.....

[RED2001GT]

My 2001 GT gets an overall average of only 12 mpg. I don't know why? I purchased the vehicle brand new in 2001 and it's still 100% stock. It's got the 5 speed manual transmission in it and it only has only 11,8xx original miles on it. In October of 2010, I did some major "wear and tear" repairs to it. All the spark plugs were replaced together with the rubber boots. I also had the fuel filter, air filter, and oil filter replaced and the axle differential fluid, the transmission fluid and cleaned the transmission filter. The power steering fluid was replaced too. Also, brand new front and rear brake pads were put on the car and I purchased 4 brand new tires for it. I've religiously maintained this vehicle ever since I purchased it brand new.

When I first purchased the car brand new, it had better fuel economy and was doing about 19 mpg. The fuel economy has dropped drastically since then and it doesn't do any better than 12 mpg right now. My driving habits are about 50% city and 50% highway. I also don't drive aggressively. I drive like an old man and I never beat on the car.
Why is my gas mileage so horrible? I should be getting at least around 18 to 19 mpg with the driving that I do, but I don't. Could there be anything wrong with my car for it to have such horrible gas mileage? Please help me out.

 

[trinity_gt]

1) Make sure the car rolls freely with no brake drag.
2) You didn't mention service to the O2 sensors. Although the car only has 11K miles, it's 10 years old. The O2 sensors may be contaminated due to age and may not be functioning optimally. However, before replacing anything get a scan tool on the car and check for codes as well as the short and long-term fuel trims. Make sure the car is going into closed loop. If you have scan tool that can plot realtime graphs (e.g. Autotap) have a look at the left and right front O2 sensor waveforms as you drive down the highway and in the city. If the response is slow or laggy, get new sensors. (If you can't do realtime graphs buit can do logging, log this data and play it back later after importing into a spreadsheet.)

 

[007]

It wouldnt hurt to hit your MAF with some electrical contact cleaner (no residue type) either.

 

[joshjwc9]

Couple of things that may impede and be hard to tell. If you are performing alot of short trips like <5 miles the car doesn't have enough time to get warmed up, remember our cars are engineered to get the best mileage at operating temp. Take this into consideration, I work for a retail store. I used to work at one that was 6 miles away form my house, where I'd get around 15mpg. Now, I've been transferred to one that is 15 miles away. I now knock down 17mpg. All while using my Vortech to see boost on occasion.

Another reason is the slide pins are seized up in the rear brakes, causing them to drag, and making the car work that much harder to accelerate.

 

[RED2001GT]

When I put the car back on the road in the spring time, I will have the mechanic check the 02 sensors and the MAF. I don't know whether or not the 02 sensors were replaced and whether or not the MAF was cleaned during the service which I had done back in October.
I know that after the service was done and when I put it on the road that I was driving on the highway for over 20 minutes at a time and I was still getting very horrible mileage. I'm hoping that the problem is the 02 sensor or the MAF.
Does anybody know how much money it costs to replace the 02 sensors and to also clean the MAF? How many 02 sensors does the 2001 Mustang GT have? Is this going to be an expensive repair job? I am not mechanically inclined and I don't know how to do any repairs to my car. I have to rely on my mechanic for everything. Will replacing the o2 sensors and cleaning the MAF cost a lot of money?

 

[93GTStang]

I would check brakes as mentioned as I have seen this on alot of cars that have sat around. If you do replace the o2 sensors get NGK not the Bosch, or get the Motorcraft.

 

[fastfoxdrvr]

Your car should have 4 O2 sensors, and I second the Motorcraft endorsement from 93GTStang.I replaced all 4 of mine in my 96 with factory replacements at 100k, no problems so far(40k to date).

 

[trinity_gt]

Your car should have 4 O2 sensors, and I second the Motorcraft endorsement from 93GTStang.I replaced all 4 of mine in my 96 with factory replacements at 100k, no problems so far(40k to date).

Only the front two sensors (one on each side) are used for fuel control. The other two are used to sense the efficiency of the catalytic converters and will have no effect on fuel economy/usage.

 

[01GT eibach]

Something is very wrong. I have never seen less than 19 mpg (or so) combined driving. With my mods, my gas mileage is almost always around 21 or so, combined. Unknowing people will refer to my car as a "gas guzzler". I tell them I admit it is no Prius, but it is a lot better than they think ...

 

[Kornnut]

Change your fuel filter. Cheap and may fix the problem.

 

[SiahNyde]

my 99 gt with 473 rwhp get 10 in town and 20 in the highway...avg is 15...that's better than yours and that's really wrong! maybe you need to beat on it! Let that pony gallop!!

 

[RED2001GT]

Change your fuel filter. Cheap and may fix the problem.

The fuel filter was changed when they did the service in October 2010. They also changed all the spark plugs and the spark plug boots. My GT was getting the same very low mileage even before the major service that was done to it in October.
Do you think that the O2 sensors are the cause of the problem with the gas mileage being at a very low 12 MPG? Or could it be something else? Also, how much will it cost to replace both O2 sensors that you are talking about?

 

[patman0911]

No codes, I presume?

12 MPG is atrocious for a stock GT but 1200 miles a year is not a lot of miles - do you drive a very short distance everyday, or does the car sit for long periods of time without being driven?

If you're driving it less than 5 miles a day round-trip then you may never be getting out of the engines warm-up mode and into closed loop operation. Short driving distances at low speeds could add up to terrible MPG. The other problem is that you might not be driving enough to complete an OBDII drive cycle so the computer isn't able to detect and report problems or make adjustments to the tune. Top off the tank, drive it a hundred miles down the freeway and then top it off again and see what kind of MPG you've got then.

If the car is sitting undriven for periods of time then maybe some of the sensors may be getting dirty or fouled by the environment and potentiometers like a TPS could get scratchy from disuse. Need to put the car on a scanner and see if the sensor reading match what would be expected. Inlet air and coolant temps should be the same as the outside air when the car is cold, and once running the air temp should get hotter than ambient as engine compartment heats up and coolant temp should get up to 190F, TPS should track smoothly as you open and close the throttle, once in closed loop the front O2 sensors should switch back and forth from below to above .7 volts. I don't know what range to expect from the MAF sensor but you should see it change in response to throttle and RPM. You should be able to see basic functionality with a cheap scanner but it might be worth taking it to a shop and letting someone with a real analyzer take a look at it.

A can of MAF cleaner is cheap and cleaning mine gave me back a couple of MPG I'd lost.

 

[Everett]

Does the exhaust smell of raw fuel. With that few miles I would expect it to run like new. I have 3.90 gears and I drive my car pretty hard and still get 25 highway which is a loss of 3 mpg but went from 16 to 19 in the city. I hope you get it figured out. Good luck

 

[GDawg]

My first instinct is where is the gas going if you are not driving aggressively. I assume that means you don't drive around at 3500rpms all the time.

Are you running rich? Probably so. Like above mentioned, do you smell gas. Is your exhaust smoking? If you are running rich and spewing HC then the question becomes why are you running rich. Is the MAF dirty and it's not metering the air correctly.

Lastly, do you have any fuel leaks around the inlet tube.

 

[wheelyman19]

Also if the car is sitting for long periods of time and is in a got environment gas will evaporate wich will make it seem like its using a lot more gas then it really is... I'd say drive the thing more then once a month to church lol

 

[bdcardinal]

and cleaned the transmission filter.

You mentioned you had a 5 speed. There is no filter on the Manual transmissions. Did a shop do the work for you? if they said they cleaned the filter that does not exist then whats to say they didnt do all the other work.

 

[twogts4us]

You mentioned you had a 5 speed. There is no filter on the Manual transmissions. Did a shop do the work for you? if they said they cleaned the filter that does not exist then whats to say they didnt do all the other work.

Scary huh?!?! I'm with ya bdcardinal... I'd swap that fuel filter again. It's cheap and easy to do. (Well, it's easy after the first time...I do recall struggling with it that first time I did it...since then I can now swap a fuel filter in just a few mins. - Link for a great how-to article for your fuel filter change --> BULLITT Fuel Filter Change)

YOU MUST USE A 5/16th inch spring lock release tool to remove the old filter.

Best of Luck!
Chris

 

[bdcardinal]

Scary huh?!?! I'm with ya bdcardinal... I'd swap that fuel filter again.

Ive seen it a lot actually. We will get people calling in asking how much parts cost that dont exist on vehicles that a shop is trying to sell them. Dont know how many times ive had to explain that Mazda 3's dont have timing belts.

 

[bevbailey]

I have a Bullitt...what kind of filter is not on a manual transmission (transmission filter??)thought the discussions was about fuel filter but I can't see how transmission filter would get into conversation, but also why a fuel filter would not be in manual car.....I'm kinda confused. I 'm having starting problems with my car as it periodically starts a bit hard and now occasionally cranks and cranks and won't start for a while (always starts fine later) and last time started with throttle but died at idle and then later is starting every time..