MAX2000JP wants me to post this question because he can't log on for some reason.

Anyway, since there are 2 FP regulators on a 5th gen, do that mean that there are 2 different fuel lines coming into the engine bay and that one would need 2 underhood FP gauges to monitor idle fuel pressure??? I'm assuming the split is after the fuel line enters the engine compartment, necessitating only 1 gauge.

 

you need 2 for the 5th gen and 1 for the 4th gen.
the 2 on the 5th gen work together(one's primary and the other's secondary)

 

When I took my intake manifold off, I could see that the fuel rail is continuous with a fuel pressure regulator at each end of the rail. Another word, the fuel rail is "U" shaped. There is 1 fuel line going into the engine and 1 return. The fuel line going in is the one feeding the front fuel pressure regulator. To install a gauge, you would tap into the fuel line before the front fuel pressure regulator. Hoon, if this info is wrong, please correct me.

 

Look at it this way...

Which is more important, the fuel pressure that's going into the engine...or that's coming out?

 

I don't understand how fuel pressure regulators work. Do they raise the pressure before or after the regulators? If it raises the pressure after, then why would they need a regulator on the return line? This is all french to me.... Maybe Nissan is just trying to compensate for putting a weak fuel pump in the Max, now I'm just talking out of my ***... In any case, I'm going to upgrade to the Walbro pump soon! Car is detonating when under stress and it is not the coils.

 

Well, FPRs (Fuel Pressure Regulators/Risers) work just like any regulator/riser... The one Irvine has on his Maxima works off vacuum however. Dependingo n vacuum, the FPR will allow more pressure or less pressure into the fuel rail. More vacuum present, less fuel pressure.

Why does it have it on the return line? This is just assumption, but, the one before the fuel goes into the rail is a FPRiser, the one exiting the fuel rail is a FPRegulator. The riser builds pressure, while the regulator opens and closes to maintain pressure in the fuel rail...but, this is just a guess.

 

From my latest findings this is incorrect.

We actually only have one FRP, the other is a dampner. The fuel comes from the pump and through the dampner (which acts merely to surpress fuel surges/spikes). Then the fuel moves into the main part of the fuel rail.

At the end of this fuel rail is the actual FPR, which works off of vacuum pressure, and has a return line. Fuel is being pumped by the pump and forced into the mail rail, and is trying to escape through the return line, but the pressure regulator is there to control how much can return. Everything that doesn't return is sent to the injectors. So, as the regulator is restricted, via vacuum pressure, it let's less fuel escape and more is forced into the injectors.

Moral of the story, only 1 FP gauge is needed.