Pontiac Repair: Innacurate Speedometer, obd scanner, pontiac firebird

Question
Hello,

I am the owner of a 1998 Pontiac Firebird, rebuilt V6 3800 Series 2 engine and a rebuilt automatic transmission.  Some time ago the rear end was replaced because it was going bad, other than that the car is just fine (regarding the power train).  However the replacement rear differential is of a different ratio than the stock rear end.  As a result the speedometer do not display the correct speed:

Example:

Speedometer reports the vehicle is moving at 56MPH when it is really traveling 50MPH.  Another example is on the highway, when the speedo says 86MPH the car is actually traveling 79MPH.

I'm pretty handy with electronics and have a OBD scanner.  My question is is there a way this issue can be fixed?  It is really annoying and I'd like to fix it.

Thank you in advanced for your assistance.  Happy Holidays to you!

- Matt

Answer
Hi Matt:

Yes it can be fixed. you need to look into one of these. http://www.streetsideauto.com/c/performance-programmers-chips/programmers/b/hype

Not for a perfromace upgrade but just to change the calibation for the speedo. that engine really is not a performance engine and you will not gain much by using one of these but you can fix your speedo. look for one from hypertech that you can cahnge the speedo calibartions. The engine control module has all the info in it for running the speedo. The dash unit just goes along for the ride from the signal it gets from the engine computer. That is going to be the easiest and cheapest fix for you.
Good luck :-}