As some one else has already stated, the 88 SEL 300 is an in line single overhead cam six. The fuel pump and pulsation dampener are located beside the fuel tank. The filter is back upstream. It has been a whlie since I have worked on one. The filter might be inside the unibody reinforcemet near the engine (under the vehicle). As to your problem, it could be the filter, pump, relay (located in the electrical box by the firewall -you need to get a manual to determine which one) or it could be the regulator which is located near the fuel distributor. I would put a fuel gage on the line at the regulator (the manual will guide you as to the proper way of measuring pressure).