Mathias,
First, since this lift has been sitting outside, pump some fuel inside a glass container and let it sit for 4 hours. If you have water in the fuel, you will see a distinct line where the fuel and water have separated. If so, drain the tank and all fuel lines. Replace fuel filters and fill tank with fresh fuel. Bleed the system and try to start. Since parts have become so expensive, I would take the pump off and take to a diesel shop. Good Luck.