420SEL No Start - Sometimes

[alsevi]

I bought a 89 420SEL at a salvage yard that looked like it had a future and drove it home. When it starts , it hits immeidately and runs fine. When it won't, it does not hit at all. I put in new plugs and monitor the fire with a timing light when cranking and it is triggering the light. I do not know alot about the fuel pump circuit. When it runs the fuel pumps hum. When it does not, they come on momentarily. Do they shut down when pressure is built? I jumped the relay 30 and 87 and the fuel pumps ran. Still no start, Smelled gas. When it starts, it starts for days. When it does not, it will then start on a random day. Flooding? Any ideas? Thanks, Al