Does the car sit outside? Maybe someone's syphoning your gas. Just a thought.

Dave Kegel

 

Today at 609 miles on the car, total gas consumption at 39.5 gallons.
About 15.5 MPG.
5 speed v8.

 

I took the car into the shop today and they hooked it up to the computer...they said they got 20MPG. Funny thing is when I took it in I zero'ed out the Trip computer so I would know how many miles they used. When I picked it up they used a quarter of a tank of gas and put 34 miles on it...I would say that is pretty bad gas mileage. Would equate to around 9MPG. What can anyone think about what else could be wrong?

 

Question: did you fill the car up and observe this, or did you just notice it on the gas gauge itself that it was 1/4 used.

Assuming that your findings are based upon the gas gauge...

Reasons for your observed findings:
1) They let the car idle for a long while (unlikely)
2) Your gas gauge is messed up (more likely). There is a TSB for an erratic gauge, and is available on this forum.

As some others have said, the gas gauge isn't the most accurate. In *most* cars, it reads high, then falls off quickly for the lower 1/2 (makes it look like you're getting GREAT gas mileage at first, but really aren't). So, just take that into consideration.

Also, take into consideration you're driving habits. I recommend finding a road to cruise at 60 mph for an extended period of time (ie-15-20 minutes). Reset your average mpg once at 60, and then leave the cruise control set and maintain that speed. You should see ~ 26-28 mpg if you have a manual.

Another thing to take into consideration is the gas itself. Winter mix gas typically yields worse fuel economy than summer mix (although, you're in FL, so that may not be applicable to you).

 

If they had it on a computer, I doubt if it was all driving. ie., neutral running at idle, on the 'puter, checking A/F ratio's. then road test for any lag, hesitatation, spurts, or whatever. Then back on the 'puter again to recheck all the codes. Did you walk away shrugging your shoulder's, or did you get to talk to a tech about it? And, did you get any sort of diagnostic print out.

On a side note, if you believe that your gauge is accurate, you probably think the oil and temp gauges are too. (LOL) sorry bout that...

 

The oil and temp gauges are more or less on/off based. If it has any oil pressure, I believe that it shows in the middle.

The fuel gauge should be somewhat accurate. Doesn't have to be exact, but it shouldn't be as far off as what it sounds like either

 

Are you still using 93 octane gas on your stock computer tune? If so, try 87.

 

Just using 93 wouldn't make his gas mileage vary THAT much. Maybe 1mpg or something.

 

Maybe not, but it eliminates a variable in the mix.

 

93 octane always makes my cars sound "grumbly" and drone a lot, as if the exhaust mixture is more dense than normal.

 

I will try and use 87oct this next time I fill it up, should be either today or tomorrow. Will get back on results on that! Taking back into the show this week prob to get the Guage chacked out, That is what the Service Manager siad he thinks it is. Sucks I can't get over 200miles on a tank....ever. Pure highway or not. After this next time at the shop... I will be putting on GTA exhaust, JLTII CAI w/ Tune...prob the 87oct performance tune. Just havent decided between Bama or Tillman?

 

One thing you have never mentioned. are you calculating milage based on trip miles or are you looking at the **** gauge. The gauge will not be accurate in gas milage!

When you go to fill up next time. see how many miles you went since last fill up and look how many gallons it takes to fill completely.

 

I filled up for the first time and it was 14.7 mpg (100% city, a few WOT shifts that nailed the limiter, lots of fumbling around, but mostly 2k RPM granny shifts).

 

14.7 is about what I get driving city and a little spirited, we are still on the poopoo winter mix gas here.

After about 1000 miles its been steadilly going up a point or two to a little over 16-17 ish. I actually heard a few detonation pings here and there(flooring it at low rpm's), so I may go up to 89.

 

Took a trip this past weekend and did a little experimenting (For what it's worth). At a steady 80 MPG cruise, I get a full 3 MPG less with the AC on. I thought that was pretty interesting, that's a lot!

Dave

 

Thanks for the info on that one.... but from what I hear driving with the A/C on is better than the mileage you would get with window(s) down or a Vert down?? Is this correct.... because here in Tampa,Fl we really can drive around with none of the above, esp. with Leather seats!

 

I have cloth seats and they're not too bad in the heat. However, I wish we had chilled seats. I didn't opt for the seat heaters because I wouldn't want to drive the Stang in MI winter.

 

On the phone with Ford Corporate now.... Taking the car in again for the 4th time in the month and a half that I have owned the car for this problem.... Last two weeks I averaged the MPG by dividing the Miles put on the car by the Gallons put in at the pump...and averaged one time 13.3 and the second time 13.7MPG. Any suggestions????

 

Did those results come while using 87 octane gas?

Also, here's a checklist of items to review (some applicable, some not) when dealing with poor fuel economy.

 

Not sure if you saw my earlier post, but does your car sit outside? Could someone be syphoning your gas? If so, you could try a locking gas cap.

Dave kegel