It sat for a year and a half? Is it a diesel? I'd bet the injectors and pump are all waxed up. Pull an injector line and check if it's blocked. You're probably going to have to have your injectors and pump serviced, and flush out all the fuel lines, replace the filter element, and have the tank/s flushed.
If the problem is only minor, there are diesel fuel treatment products that can help get the moisture (diesel is hygroscopic, meaning it absorbs water out of the atmosphere) and waxing out of your fuel system.