Code 42 and 66

I have a 91 chevy corsica, 3.1 motor. 130,000 miles. It is having some problems. It will stall at stops and while driving. When it stalls, it will start right back up. But, every now and then when I turn the key, it acts like the battery is dead. After trying a couple times it will turn over. It sputter and backfires at all speeds. I ran codes, came up with 42 and 66. I found 42, but really don't understand it(I only know the basic car stuff) and 66, I can't find anywhere. Someone mentioned crank sensor before, I have a feeling it can't be that easy. Can anyone help me out? I can't afford to take it to a garage and need a safe car to haul my kids around in. Thanks!