how do I fix my spark knock

I have a 95 blazer 4wd with 72,000mi on it. It gets the spark knock noise when I accelerate up to about 55 mph. I tried putting mid-grade fuel in it and it is still happening. I read that if it continues it will damage the engine. Can anyone help me as to what I can do? Thanks.. Nathan

You are likely looking at an EGR issue... is the ping severe or "trace" knock? Bear in mind also that as a vehicle ages, its octane rating requirements also rise... Ray

I agree it is more than likly an EGR problem.You should also check your timing as your base timing may be off.