Speedometer/Tune Question
Thread Starter
Joined: Jun 2018
Posts: 10
From: NC
Speedometer/Tune Question
I just bought a 2012 GT that already is modified. The speedometer is about 20mph off. I know that you need a tuner to change the calibration. I know the car has a unknown tune in it that seams to work well. My question is for now can I buy a tuner to change the calibration and somehow save the tune that’s in the car? I’m sure I will fine tune it later but for now just want the speedo to read correctly. Tired of watching slow to react gps speed on my phone.
Thanks!
Thanks!
6th Gear Member
Joined: May 2006
Posts: 11,883
From: Nicely done
when you plug in your tuner and change the Revolutions Per Mile or gear ratio, the tuner will download a copy of
your current tune and will then upload with your change (keeping the original tune).
Banned
Joined: Jan 2018
Posts: 2,327
From: Pennsylvania
Tires are the main reason for speedo correction, and 20 MPH off is way high
for tires. 20 off sounds like the gear ratio is not being calculated, so I would
guess you have a manual transmission. You can get away with not correcting
the gear ratio with manuals, but the speedo will be off.
Depends on the tuner, there could be a option to adjust it from the parameters
menu. When you change gear ratio with a new diff, it should be auto corrected
because that puts the gear ratio into the PCM. IT should recalculate it based
on the differential.
Using automatics mostly, I have never had to correct the speedo with a differential
swap, putting the new gear ratio in. Did not matter, if I did not put the new gear
ratio in, I got an Engine Over-speed condition and it went into limp mode. Once
I put that in, it was fine and the speedo was fine. So, we can only guess that it's
a manual trans, and the ratio wasn't put in the tune....
for tires. 20 off sounds like the gear ratio is not being calculated, so I would
guess you have a manual transmission. You can get away with not correcting
the gear ratio with manuals, but the speedo will be off.
Depends on the tuner, there could be a option to adjust it from the parameters
menu. When you change gear ratio with a new diff, it should be auto corrected
because that puts the gear ratio into the PCM. IT should recalculate it based
on the differential.
Using automatics mostly, I have never had to correct the speedo with a differential
swap, putting the new gear ratio in. Did not matter, if I did not put the new gear
ratio in, I got an Engine Over-speed condition and it went into limp mode. Once
I put that in, it was fine and the speedo was fine. So, we can only guess that it's
a manual trans, and the ratio wasn't put in the tune....
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