I have a 2007 classic that is bone stock except the exhaust that trows the code when i pull a trailer. Here is what i have done.New ac delco fuel filer, Cked the fuel tank for trash,used a vacuum gauge to ck fuel line restriction and it's no more than my o4 took it to the dealer they ran checks on it and said to replace the high pressure valve so i did. It still does it!!! HELP.