hi. I recently purchased a 2005 Monterey with a 350 mag mpi. 350 hours on engine. The owner hadn't used it in 3 years. He said he drained the fuel and replaced both fuel filters on the injection pump which he showed me. The test drive went flawless and we purchased it. 2 hours into our first drive the boat engine started sputtering. We were towed in. I pulled the fuel filters and they were black with debris. I pulled the siphon tube and pumped the fuel tank dry. The fuel looked terrible. Evidently this was floating on top of good gas. Replaced the filters and primed and added fuel. Engine still not running well. Pulled the injectors and tested them and 2 were totally blocked. Replaced all 8 and flushed the fuel rail. Debris came out. Engine still sputtering. Hooked up a pressure gage to fuel rail and I'm reading 90 psi. Other forums I read say deliver pressure should be around 45 psi. I understand low pressure causes a problem but can hi pressure cause sputtering. The fuel rail has a sensor on the end with a vacuum line hooked to it. It T's to the top of engine then goes to top of fuel pump. Im guessing it stops the pump to regulate pressure. The second line on the fuel rail which normally is fuel return is factory terminated and isn't a return like I've seen on some car engines. Im guessing coast guard regulations require fuel return not used in a boat and they regulate fuel pressure with this vacuum line? To replace the Guage I'd have to replace fuel rail? Or maybe the sensor is on the top of the fuel pump? Thinking about taking the water cooled pump off and opening it? Please help. Any advice is greatly appreciated. Thank you
