I have an Onan QG 5000 in my RV that is 4 years old and only has 40hr on it. I bought it brand new directly from Cummins when the upper bearing on my last one scattered ball bearings throughout the unit. All of a sudden the generator will run great for about 10min before the exhaust heats up and throws code 58.....every time. This happens under load and not under load. The engine is clean and I run the unit monthly as recommended when it is sitting idle. I replaced the fuel lines thinking it might be sucking air and also put a new fuel filter on to make sure it wasn't restricting fuel flow. I replace the air filter, oil filter, and oil every year. The air filter doesn't have a spec of dirt on it. The fuel pump has plenty of gas flow coming out of it so I know its not a fuel feed issue. The carb is clean and I even filled it with Amsoil foaming carb cleaner and let it soak to make sure then drained it. It doesn't surge and runs great when its running. The exhaust blows hard so I don't think a critter crawled up in there and nested or anything to restrict output. It does start a little funny sometimes. Almost like only one cylinder fires off and then the other doesn't fire off for a while. I sometimes have to hold the button for a few extra seconds after it initially fires to get it to keep running. I am thinking it might be one or both of the magnetos but haven't pulled the unit out of the coach to get to them. Perhaps there is a way to access them or test them without removal. The service manual I have doesn't even list diagnostic procedures for Code 58. Any help that you guys might be able to lend would be appreciated.
