Start problems

This is driving me nuts - I have a 92 B250 van that has an intermittant starting problem. The motor is a 318 with only 60k on it. It acted as though the crank posistion sensor was bad. I had spark and gas pressure but it would just crank with no start. I removed the CKP connector so I didn't have to worry about that being intermittant. I thought I measured an open ground. A week later it wouldn't start. I replaced the CKP. The new CKP seemed to make it start much faster, but a week later I am back to no start. I 've checked all the wires up to the computer from the crank and cam sensor. I added extra grounds from these connectors to the engine block. I have 9 volt power to both sensors and a clean 5 volt signal outputted from both. I'm using a scope to check the outputs. It seems to have starting problems after a 10 or 20 mile trip. It's been in the 100's for several weeks but the van temperature is running normal. When it runs it all seems normal. No error codes are being reported. I've cleaned the computer connector. Being intermittant it is a situation of being in the right place at the right time, which hasn't happened. Anyone have any ideas or know of something else that could be intermittent and cause this? thx bg