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Speedo is off , How do I fix it ?

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Old 05-01-2010, 09:37 PM
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Default Speedo is off , How do I fix it ?

My speedo is off by 5 mph. The gauges say I am doing seventy mph but in all reality i'm going sixty five mph. Any thoughts
Old 05-01-2010, 09:45 PM
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only mod is slp skip shift and borla exhaust
Old 05-01-2010, 10:10 PM
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If you get a handheld tuner you can adjust for tires I think?
Old 05-01-2010, 10:32 PM
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wheels and tires stock sizes
Old 05-02-2010, 09:42 AM
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Could the skip shift eliminator have skewed my speedo ?
Old 05-02-2010, 10:08 AM
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Every GM vehicle I have had has been off by at least 3mph (speedo showing faster than I was truely going).
Old 05-02-2010, 10:58 AM
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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.
Old 05-02-2010, 11:21 AM
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tires are 245/45/16 and the rear is stock
Old 05-02-2010, 06:02 PM
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Ya, just get a handheld tuner and fix it! Never seen a car off that bad with stock tire size tho.. that kinda confuzzles me!

Vince
Old 05-04-2010, 06:22 AM
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where do you find a handheld tuner? I've got the same problem on my 88 gta.
Old 05-04-2010, 07:29 AM
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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?
Old 05-04-2010, 10:26 AM
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What about gears? I have 3.73's and my speedo is off by 4 mph.
Old 05-04-2010, 08:01 PM
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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.
Old 05-05-2010, 05:57 AM
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Originally Posted by greasemonkeysoldier
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?
This is not common at all !
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.
Old 05-07-2010, 09:39 AM
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Should I take it to the stealership ? Yeah I bought it used from a 60 year old man
Old 05-07-2010, 03:07 PM
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Originally Posted by jaysan
Should I take it to the stealership ? Yeah I bought it used from a 60 year old man
Um - no. What do the gauge faces look like? Are they the original black ones?
Old 05-08-2010, 08:24 AM
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Originally Posted by jaysan
Should I take it to the stealership ? Yeah I bought it used from a 60 year old man
No reason to use a dealership, no warranty, overpriced and they are not always up to date on aftermarket parts, such as rear end gearing.

A qualified mechanic would be my advice.
Old 05-08-2010, 08:39 AM
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Originally Posted by 96blackta
What about gears? I have 3.73's and my speedo is off by 4 mph.

any shops near you? they can correct that for about $25-$50.
Old 05-08-2010, 09:14 AM
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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.
Old 05-08-2010, 08:27 PM
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Originally Posted by wssix99
Um - no. What do the gauge faces look like? Are they the original black ones?
yezir , and I have the stock rear end


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