Hi all. New member here thanx to the 2007 Mustang I recently purchased. I took it to work the last month and noticed that the odometer registered the trip as 1.6 Kilometers (yes...I'm in Canada) more than my other cars. I checked the speedo using my GPS and discovered it was out by quite a bit. At 60 KPH (about 38 mph) my GPS shows I was only doing 50 (31 MPH) , and at 120 (75 MPH) GPS said I was only doing 100 (62 MPH). I had it checked by an independent shop and the tire size (P235 55 Zr17) was programmed correctly with a 311 rear end. I took it to Ford (twice) and they played with for an afternoon while it was connected and I went along for the ride. Long story short, they couldn't fix it. The Ford program only allowed 4 different options for tire size and two for rear end differential and none of them seemed to make a difference. I checked the forum and it has been addressed before but nothing offered seems to apply. I think 13 MPH out at hiway speeds is a little bit too excessive and Ford has no idea how to fix it. I bought it used with VERY low mileage, and if this has been going on since new, I figure it has about 1200 miles more on the odometer than it has actually driven. Other than that, I am enjoying the car and it is just plain fun to drive. Any help or suggestions would be appreciated. THANX!!

 

The factory gears should be 3.31 not 3.11. That may be your issue. I would verify the gear ratio before going any further.

 

Sorry...I meant 331. Was going from memory. The tire size and diff were set to default setings.

 

Sorry I can't be more help I have not had this issue. By the way welcome to the forum!