[scca_ev]

I searched other speedometer threads and didn't see this situation addressed.

I recently purchased an 02 GT with OEM 3.27 rear end ratio. The speedo reads fast by about 8 MPH at 50. I plugged in my handy dandy code reader and looked at the VSS speed. The VSS says I am doing 50 at 50, but the speedo is reading fast. This tells me it's not a VSS issue, but an actual speedometer issue.

Other than the recalibration tool is there a way to adjust the speedometer calibration? Not sure what the effect would be of recalibrating the VSS signal will be to account for an inaccurate speedometer.

 

[SoCal2V]

Is it off by 8 mph at all speeds, or is it off by a percentage of vehicle speed?

Not really sure how this could happen. Does the car have and aftermarket gauge overlay? If so, the needle may have been reinstalled incorrectly. I know when I did mine I had to play with it a little bit to get it right, as it wanted to read a little high as well. What I did was, remove the peg that's just below "0 mph" and then put the needle on so that it was pointing to just below where the peg sits, then lift the needle up some, install the peg and when I let go the needle went all the way down and rested on the peg like it should. The reason why is, there is a slight amount of sprung preload and just sticking the needle on there it wanted to lift it a little - it's been a long time but I seem to recall pointing the needle at "0" and when I let go it lifted up to "5" mph or so.

Hope that makes a little sense anyway...

 

[scca_ev]

Gauges "look" factory, but ill google. It's a percentage off at all speeds.

tx

 

[scca_ev]

Looks like this one but not pegged http://www.allfordmustangs.com/foru...21-help-speedometer-pegged-150mph-photo-4.jpg

 

[SoCal2V]

If you have white gauge faces like that (and your car is not a Cobra) then it has an aftermarket overlay.

 

[scca_ev]

If you have white gauge faces like that (and your car is not a Cobra) then it has an aftermarket overlay.

who would have thunk...

Thanks.

 

[wmburns]

I searched other speedometer threads and didn't see this situation addressed.

I recently purchased an 02 GT with OEM 3.27 rear end ratio. The speedo reads fast by about 8 MPH at 50. I plugged in my handy dandy code reader and looked at the VSS speed. The VSS says I am doing 50 at 50, but the speedo is reading fast. This tells me it's not a VSS issue, but an actual speedometer issue.

Other than the recalibration tool is there a way to adjust the speedometer calibration? Not sure what the effect would be of recalibrating the VSS signal will be to account for an inaccurate speedometer.

Please note that for the 99-04 model year, the output of the OSS goes only to the PCM. The PCM "tells" the speedo what to display.

So if the ODB2 speed is correct, then using a recalibration tool is not really the technically correct way to fix this.

If your car is a manual, likely you could get away with it. The only problem I could see is perhaps the speed limiter.

If your car is an automatic, then consider that the PCM will use the car's speed to determine the automatic shift schedule. Therefore recalibration would fix one problem in exchange of a new problem.

Is it possible that someone has used an 150 MPH overlay on a 120 MPH cluster?

 

[scca_ev]

Is it off by 8 mph at all speeds, or is it off by a percentage of vehicle speed?

Not really sure how this could happen. Does the car have and aftermarket gauge overlay? If so, the needle may have been reinstalled incorrectly. I know when I did mine I had to play with it a little bit to get it right, as it wanted to read a little high as well. What I did was, remove the peg that's just below "0 mph" and then put the needle on so that it was pointing to just below where the peg sits, then lift the needle up some, install the peg and when I let go the needle went all the way down and rested on the peg like it should. The reason why is, there is a slight amount of sprung preload and just sticking the needle on there it wanted to lift it a little - it's been a long time but I seem to recall pointing the needle at "0" and when I let go it lifted up to "5" mph or so.

Hope that makes a little sense anyway...

Promoted by this post, I double checked the difference at all speeds, and sure enough it's the same across the entire range.

SoCal, thanks for the tip :worship. It looks like the needle positioning is the problem. I guess I can either live with it, or pull the dash and reposition the needle on the pin.

Now, does anyone need a recal box? :bounce2:

 

[Snoopius]

I searched other speedometer threads and didn't see this situation addressed.

I recently purchased an 02 GT with OEM 3.27 rear end ratio. The speedo reads fast by about 8 MPH at 50. I plugged in my handy dandy code reader and looked at the VSS speed. The VSS says I am doing 50 at 50, but the speedo is reading fast. This tells me it's not a VSS issue, but an actual speedometer issue.

Other than the recalibration tool is there a way to adjust the speedometer calibration? Not sure what the effect would be of recalibrating the VSS signal will be to account for an inaccurate speedometer.

I'm not sure what the percentage rate is of tire size/speedo inaccuracy, but is it possible you have non OE sized tires on your car?

 

[scca_ev]

I'm not sure what the percentage rate is of tire size/speedo inaccuracy, but is it possible you have non OE sized tires on your car?

Thanks for helping.

I did however figure out it was not a percentage, but off the same across the scale. This means the needle wasn't put back on right when the whiteface gauge overlay was installed.

Tx again...