Help- Speedometer reading is way off.

[fastjack1]

The reding is way off between my stock speedometer on my 87 GN & my OTC2000 meter . 5 mph on speedometer reads 15 on the OTC. 30 on the speedometer reads 50 on the OTC. 60 on the speedometer reads 95 on the OTC. Tire size is P215- 65R. The readings are only 2MPH difference on my 86GN so I know that the OTC meter is working correctly. Who knows what the problem is. The stock computor has been modified for low impedance injectors, if that makes any difference. Thanks.

 

[BlackBandit]

If the speedometer (the gauge) is reading correctly I would suspect the VSS.

 

[DavzGN]

is it the stock 85 mph or is it a 145mph replacement? If it is the 145mph replacement, it could be a reducer causing the problem.

David
87GN

 

[mikestertwo]

is it the stock 85 mph or is it a 145mph replacement? If it is the 145mph replacement, it could be a reducer causing the problem.
David
87GN

If he had the 145mph speedometer and it was calibrated correctly with a gear reducer I would think the OTC would read lower.

 

[fastjack1]

It is the stock 85MPH speedodometer

 

[fastjack1]

Where is the vss located and will this effeck the cars performance?