Re: Nissan 3.5 B2 faulty fuel tank
RBib,
Welcome to the forums. You replied to a 6-year-old post; I hope the OP resolved his issue by now.
If a crack develops in a plastic tank, it must be replaced. Nothing we have tried works for long. That's also true of the 3- and 6-gallon remote tanks of any brand.
I have a fleet customer with MFS4A2 motors (your vintage) that were having fuel problems, primarily water contamination. Not sure whether they were buying the gas that way, or whether the problem was happening at their base. But it was a repeat clean-the-carb-and-flush-the-fuel-system issue. After a lot of service trips, and much speculation, I supplied them with a baja-type water-separating fuel funnel, and the problems magically went away. Keep in mind that the 4/5/6 has a very lean carb setup to satisfy EPA, and as a result, carb varnishing (worse with modern gas) can only be corrected with a complete carb disassembly and a soak in real carb dip. If there is water corrosion in the passages, the carb dip will not remove that, and the carb must be replaced.