Pontiac Repair: speedometer reads twice as fast and tach reads high, pontiac grand prix, engine computer

Question
I have asked you questions about this 1990 Pontiac Grand Prix before and you have always been on the money so I have another. Ever since we got it the speedometer has read twice as fast as really going and the tach reads high. We needed to drive 155 miles one way to go to a hospital where our son in law had brain surgery and could not take the car because it was not working. Can you give us some insight into what could be causing it? Thank you. We really appreciate all of your help. The car is running great now. We had to have someone take us to the hospital and we felt like a burden.

Answer
Hi Trudy:

no other direability issue other then the IPC issue?? does this have a low coolant light on all the time? any other warning lights on? does the temp and fuel read correctly?  If it was just the speedo I would venture to "guess" it's a bad engine computer that year car had all kinds of engine control module problems. Beinf that the tach is readin hi to would make me think that you could just have an issue with the IPC (speedo) cluster. with out seeing it I don't know for sure Both of those inputs to the IPC need to be tested to see if the induced input matches what it should on the speedo and the tac If the induced input to the cluster results in the proper reading then the issue is with the engine computer. if not then the IPC is the culprit. good luck :-}