Well the new parts describe half the cars, only one of the cars was born with a charcoal canister and it is disabled. My guess is that the aftermarket pumps, most of which are new, don't have check valves in them allowing the fuel to drain back, further I think the fuel may be boiling in the line running on the frame rail by the exhaust manifold (factory, everything correctly located and in good shape). The key may be in the quality of fuel which I haven't completely resolved in my head. Most are parked on level surfaces so the line hiegths are correct and prevent drain back into the tank. No fuel leaks that are noticeable under pressure. Not arguing with the ideas just thinking through then out loud. I need to start looking at the fuel filters before fire up to make sure it is what I think it is but I cant imagine it can be anything else the way they act.