I have 1998 mustang gt that I got like a year ago, dont really know all the mods that have been done to it. I always had a problem with a speedometer being off by 5 miles, so if I drive 35mph it shows 40mph. I figured that I got some Gears installed by previous owner. Recently I got me a Diablo sport tuner and tried to change gear ratio, but diablo sport do not let me choose gears. So how can I find out if I have gears installed or not? And how can I fix speedometer problem? Thank you for responces in advance.
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bump, maybe someone know something or not?

 

the speedometer is not controlled by the PCM, therefore you cannot change it with a tuner. The only way to fix the speedometer on thesn95s is to either get a speedcal from dallas mustang, or to change the speedo gear.

Does your car have gauge face overlays? If so, the needle could have been put in the wrong place with reinstalled. If it is a constant 5 mph off at all speeds, then I would imagine that this is your problem. If the car had different gears it would be off by a smaller amount at low speeds (say 2 mph) and more at higher speeds (say 10 mph).

 

+1

 

++1 if you have gears it will be an expontential increase through speeds. example : 20mph = 24 mph ...... 60mph = 75 mph.....etc.

 

+1

 

Thank you for your help

 

Oh by the way, one more question, is it any way to check if I have aftermarket gears installed?

 

How fast does your car go at 5000 rpms in 2nd?

 

will check it out tomorrow.