96 4.3 vortec excessive pinging

I have a 96 s10 with a 4.3 vortec. My engine pings heavily under any acceleration no matter what grade of fuel I use. Every one tells me you can not adjust the timing on this model engine, that it is automaticly controlled by the computer. Could there be an engine component that is bad causing the computer to not set the proper timing curve? If so where should I start looking?