I'll try to make this as short as possible. I bought a 91 civic for $100 with 90K miles on it. I was driving it home, it made it about 40 miles before it crapped out. Before I bought it, I picked up a distributor from a junkyard in order for it to start. I had it towed home and replaced the battery because I'm sure it was old. When I would try to start it after that, it would just crank, and then it would have a "ping" noise that sounded like it was coming from around the gas tank. The ping would happen every 4 or 5 seconds when cranking the engine. Everybody that I've talked to said the problem is the main relay, go replace the main relay. I took out the old main relay and tried to start the car just for the hell of it. It would constantly crank, but the "ping" noise went away. I put the new main relay and it went back to cranking with the "ping" noise every 4 or 5 seconds. Sometimes with the relay in, it sounds like it wants to turn over but just doesn't do it. I have no idea what the problem could be. This is my real first attempt at working on a civic, but I really need to get this thing running. Any help or ideas that anybody has would be very helpful.

Thanks,
Jon