1988 Ford E-Series Van To much fuel

I have a 1988 Ford E250 van and it loads up on fuel like a rich running carb but its fuel injected. It fouls the plugs about every 6 months because it gets to much fuel and when you change them you can see the gas on them. When I'm sitting at a stop light it loads up and wants to cut off I put it in N but this just helps but it still runs rich. Sometimes when you go from a dead stop it will cut out and back fire. I try to keep it in good running order I have changed the plus and put a new fuel pressure reg on it but that didn't fix it. Thank you for your time hopefully you can help