Sometimes just guessing what is causing the problem and replacing it will fix the problem but by using the guessing game you usually end up just buying extra parts before the real cause of the trouble is found. You might get lucky with the relay replacement, it is a pretty good possibility. Before replacing anything I would first find out what area is causing the trouble. It could be an ignition problem and not a fuel issue. Using the starter fluid trick is an easy way to pin down the area of trouble.