Originally Posted by Danthurs
The engine I have has no FPR, it'* a single fuel line.
Understood. But... this in itself does not mean there is no regulator in the system.
There must be a regulator in the system at some point, because if there wasn't, the pressure would be unstable, and would be whatever pressure the pump was putting out. This would just not work very well.
Either the pump has a regulator build into it, (has a some type of relief valve that lets fuel return into the fuel supply, etc.) or there is a regulator located down stream of the pump. Not all EFI systems have return lines, but as best as I can recall, they all have regulated line pressure.
Since the regulator can not be purchased as a separate part, I'd suspect that it is part of the pump.
The line pressure can not be the same as the pump pressure, if you know what I mean.
A line pressure test is kind of limiting, in that, it may show that the pressure is low, or that the system isn't holding the line pressure as long as required after the pump has been shut down, but it will not tell what the cause of the problem is. Low pressure can be a weak pump, or the regulator. Leak down can be caused by a number of things.
If it starts cold, why do you suspect the fuel system? Seems that it would have more problems starting when it was cold if the fuel system was at fault. Unless it was flooding, or vapor locking when it was hot. And since EFI isn't suppose to vapor lock, it kind of narrows it down. Just saying....Its just something else to consider.