The episode you speak of is indeed a Growing Pains episode. The Grandfather dies, and Mike Seaver (Kirk Cameron) sees the grandfathers ghost jogging into the back door and through the kitchen. The Grandfather didnt come into the Kitchen for a drink, but Mike did. He came into the kitchen, takes the milk carton for a drink, watches his grandfathers ghost enter the kitchen through the back door, says "Hi Mike." and keeps on jogging through. Mike drops the milk carton onto the floor in shock.
Growing Pains - I had completely forgotten that title.
The idea that grandfather did not know he was dead stayed with me as I've heard that notion before. I think that WAS the situation, was it not? He did not realize he died?
And Kirk Cameron, I have not thought of him in ages.