Read this article for information on how to read codes without a scanning tool. Basically, all you need is a wire or paper clip to read codes.
Do it yourself EEC IV Diagnostics
Sorry for the bad link. As long as I'm editing I may as well mention that a code reader is not required to read codes.
I would say that the age of your sensors has more to do with it than the age of your engine.
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351W 89 Mustang GT Convertible
[This message has been edited by jimberg (edited 07-22-2001).]