Good evening all, hopefully someone here will be able to give me some insight as to what my problem might be. I have an ’07 GT with automatic. In spring of this year I installed an MRT cold air intake and started running a Brenspeed 91 octang performance tune. I ran several months without any issues. In-town fuel economy was in the 19-19.5mpg range, and lengthly freeway jaunts saw returns of up to 26. Some time in June I switched over to Moble 1 synth and ran another couple of months with no appreciable change in the fuel economy numbers. Please note that there have been no changes in the gas I use… 91 octane from the same station, with only a couple of exceptions on the station used when on trips. Also take note that my driving habits haven’t changed with regards to length of work commute, time or distance.

Some time in September I noticed that I was filling up with greater frequency then normal. Since then I have been monitoring the onboard fuel econony numbers pretty regularly. To my dismay the numbers had fallen to around 15mpg in the city. Recently I took the first long freeway trip since noticing the problem and maxed out at 20. That’s a decrease of 5mpg with no changes in gas used, driving habits, or any other non-cosmetic vehicle modifications.

So now I ask you all, what could the issue(s) be here. Aside from taking it to the dealer, what are some of my options for determining what is wrong? Thanks for your time!


For complete vehicle details, Click to view the Sytrus Signature Page

 

You could try reloading the tune, but I doubt that would help. Something might be fouled/gummed up. Try running a tank of gas with some Techron Concentrate in it. You can find it at any auto parts store. Don't skimp out and get the cheap stuff, get the Techron, it is safe and works good.

 

I would suggest the same as above, unload and reload the tune. Take a shot here ask what you mileage on the car is? Maybe time and swap the fuel filter out for a new one as well.

 

I`d check to see if it has any trouble codes.

 

I run a can(full tank) of that BK44 injector cleaner in my cars every 20K miles.Its pricey at $22.00 for a little can of that stuff but it works great.As mention the fuel filter needs changed, at least every 10-15K miles.With my latest engine upgrade my fuel milage has gone by-by down to 23mpg hiway.

 

+1 for typical checks:

1.) Reflash - car "learns" driving habits.

[Trips over 50 miles without aggressive throttle inputs allow the car to drift back toward factory tune.]

2.) Fuel Filter - standard replacement intervals should be fine.

3.) Tranny - doing a bunch of Hwy speed "punching it" could put some wear on transmission bands. Had this issue in the past with auto tranny. If you change the fluid it may alleviate the issues. You may have to "investigate" third gear. What happens is the bands burn up when you hit it all the time on the highway and then when you're cruising at 65 it slips a bit and then you lose mileage. There are tricks to checking this out with a borescope. Ask a tranny expert.

4.) Dragging Brakes? Ford has an issue with the e-brake on these cars. Note the pad wear in the back vs. the front. If you see difference, put the car on a hill and try to roll backwards. If it doesn't seem free, take it in as Ford has issued a TSB.

Good Luck.

 

There is a good chance it is your gas, even though you have not changed stations. It is possible you are getting the reformulated gas used for the winter months. You may want to check with your gas company and see if it applies to your area.

I was using reformulated gas in Minnesota and noticed a dramatic drop in mpg versus "pure" gas when I was away from the twin cities, and refueled.

I now refuel outside the city limits, in Western South Dakota, and get pure gasoline (no alcohol, or reformulation products). My mpg is a consistent 24.6 on the highway at 75.

Just a thought...

 

that was my first thought also. Winter blend. Where are you located Chris? Probably won't matter that much but check your tire pressure with the colder temps coming.

 

Thanks to all for the responses!!! Let me see if i can answer all of the questions:

• Mileage is right at 8500.
• Live in Sacramento, CA and use (ducks head...) Costco gas.
• Just visited Les Schwab last weekend and had the tires checked and rotated.

I have a laptop available so I will hook up the SCT and check for trouble codes, hopefully this afternoon. I will also check the brake pads as Shaun suggested.

 

Once your PCM is flashed, it remains that way. It can't "go away" by itself or reset itself to stock after a few thousand miles. If you think it does, it's all in your head because the stock tune is stored in your X-Cal 2 / LiveWire / X-Cal 3, not in the PCM.

 

run some injector cleaner thru it.i bet the charge motion plates are getting some build up on them.the96-98 dohc cobras had this problem bad.

also you live in the famous state that jacks with the blend of fuel,so that could be some of the issue there.

 

I just got done with the SCT and laptop hooked up to the car... no DTC's (trouble codes) found.

 

chris ,same has happened w/ mine,but I think its due to being a garage queen now(before it was a daily driver) and only using it for short jaunts and getting on it somewhat. I have 9500 miles on mine

 

Yes he lives in a state that changes blends of fuel and this alone could be his cause.

Richard

 

Knowing that you live in a State that has "Winter Fuel" I concur, probably nothing mechanically wrong. Unfortunately WI went to 10% Ethanol year round, so we have terrible fuel all the time. My 5-spd GT w/3.55s still gets 21 avg. City/Hwy. I can pull about 24 Hwy on RFG. I found a station that sells "Real Gas" and I pulled 27 MPG Hwy.

 

I realize this may be obvious, but also check the air pressure in your tires if you haven't recently. I just had new tires put on my Honda, and noted about a 30% drop in fuel economy afer a tankful. I checked the tires and they were at 26 psi. I pumped them back to around 34 and the gas mileage came back to normal.

 

Have you checked with your sct tune if your cooling fans are set to come on earlier than the stock temp settings? With the colder weather and the fans running earlier the ECT sensor may be telling the PCM to run rich.

 

It probably wouldn't make it run rich, the thermostat will overpower the fans any day. It could however, cause an electrical draw on the system, causing mileage to go down slightly. I doubt more than .5mpg though, so that likely is not the problem.