We have a 2001 Phaeton with the 7500 Onan diesel and I had serviced the generator and it had run fine before we had left on vacation. We left about 2weeks later and when I went to use it If didn't want to start or would not run very long, I thought that I had installed the fuel filter wrong and had air in the lines. When we returned home I took it to our motorhome mechanic and he found the fuel lines were bad and changed them. It runs perfect now. I bought the motorhome new and I guess after 20 plus years they deteriorate.