Help! incorrect instant and average fuel mileage

[kwlong]

Could anyone give me some direction as to how to solve my displayed mileage problem. My indicator goes to 99 mpg right away, used to work fine. Is computation done in the ECM?

 

[stang-etr96]

I believe its done in the CCM, could be wrong about that, I'll have to check when I get home from work.

 

[TedC]

kwlong, Welcome to CAC!!! I suggest you try searching this site before opening new posts. Most times someone else ran into a similar issue and discovered a solution. Based on your description, this seems very similar to an issue I had on my 1989. Take a look at this post. http://www.corvetteactioncenter.com...-reporting-incorrect-average-instant-mpg.html

Another sign that the ECM is defective is that the upshift light will go on and off for no apparent reason. This should not happen with an automatic.