Speedo is off , How do I fix it ?
if you can find someone with hptuners they can edit your speedo. what size tires are you running? smaller tires than stock will make your speedo go faster and if you have gears in the rear end, higher gears will do the same thing.
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i've got this same problem as well....as has been stated before i assume this is a very common thing. mine is off by about 5 mph at lower speeds and 10-12 mph off at higher speeds (i.e. 60-70 mph) the Tach is also off. I found out it was off when i had it hooked up to HP Tuners doing some logging. so the PCM is putting out the correct mph/rpm....but my gauges aren't. How could this problem be fixed? and how would you go about recalibrating the PCM if that is the fix?
Get a portable GPS, put it in map mode and drive down a straight road. Test the car at different speeds and if you are off by 5 mph in all of them, then you just have to move the needle on the post it sits on.
i've got this same problem as well....as has been stated before i assume this is a very common thing. mine is off by about 5 mph at lower speeds and 10-12 mph off at higher speeds (i.e. 60-70 mph) the Tach is also off. I found out it was off when i had it hooked up to HP Tuners doing some logging. so the PCM is putting out the correct mph/rpm....but my gauges aren't. How could this problem be fixed? and how would you go about recalibrating the PCM if that is the fix?
These 4th generation f-bodies have very accurate speedometers.
To the original poster, did you buy the car used?
If so, they might ave swapped gears in the rear end and not re-calibrated the PCM. If thats not it, something else is wrong, hiring a qualified mechanic would be my advice.
My PCM reported being 5MPH off compared to a GPS on a clear night. I made multiple changes to the speedo calibration through HPTuners and eventually got it within 1MPH. I wouldn't be surprised if it falsely reported slightly faster from the factory.