Had an usual for me amt of fruit juice tuesday (oj, grape) maybe 4 x 8 oz in all. diarrhea ensued yest amd continued all eve ito 3 am! cause & effect?

Learn by osmosis: The types of sugars in the juice can draw water out of the intestinal walls and into the lumen: by osmosis. When the sugars cannot be digested (eg if sorbitol is present), then crampy diarrhea ensues.

Prime suspect: Has it stopped? If yes, it was probably the excessive fruit juice. Don't do it again to test it. But, if it's still happening, whatever it is, consider a doctor's exam and drink water to avoid dehydration. You also might ask a pharmacist for OTC advice until you see the doctor.