94 E150 Bad ECU/Wiring problems?

Few months ago, van wouldn't start, fuel pump silent, starting working again. Now van wouldn't start again. Replaced ignition module, van runs, won't accelerate if gas pedal pushed more then 1/4 of way down. Check engine light steady lit, computer unresponsive when trying to read codes. Also, overdrive button quit working at the same time. Could this be from bad ECU? If so, how can I test it, & what could have caused it (i.e. short, bad wiring, or other component failure)? :banghead: