Define: Retrun Style Fuel System

[ekopel]

Can someone define the difference between a returnless and return style fuel system and its applications. I also googled it and got horse shit. Just looking for a basic definition and basic pros cons, etc.

thanks.

I also searched on TN.

[toyomoho]

On the return system fuel is pumped to the fuel rail. A pressure/flow regulator at the end of the rail moderates how much fuel is returned to the tank via a separate fuel line.

On the Camry, engine manifold pressure is used to control the regulator and thus fuel pressure. High manifold pressure equals more fuel returned to the tank, low pressure equals less.

Returnless system has the pressure regulator in the gas tank. Only one fuel line goes to the engine fuel system. The pressure regulator maintains the same pressure regardless of amount of fuel flow.

[Eye8Pussies]

basically, if you want to run high boost or high horsepower applications, a return-style fuel system is what you want since you can then add the adjustability of a fuel pressure regulator and turn up the pressure to the fuel injectors

[Buurin]

Originally Posted by Eye8Pussies

basically, if you want to run high boost or high horsepower applications, a return-style fuel system is what you want since you can then add the adjustability of a fuel pressure regulator and turn up the pressure to the fuel injectors

Theoretically, can't that be done with a regulator on the one fuel feed line?

[Eye8Pussies]

^ yes and no....the ppl with the gen4 returnless fuel systems often crush their fpr at the pump to increase the fuel pressure, but it only works to a certain extent


the only way to really get the adjustability that you need is by having a return style system- that way, the fpr is at the end of the fuel rails and you can use the most powerful pump that you can find to make sure that enough fuel reaches the "last" injector and that the injectors before it doesn't use up all the fuel first, and then adjust the fpr so that enough fuel will stay in the fuel rails before the excess is released back into the tank.

with a return-less style, you can only force so much fuel through the fpr at the fuel pump, and if you get too powerful of a pump, you can increase the pressure too much, and if it's not powerful enough, there won't be enough fuel to reach the final injector on the rails (which has always been a problem on the boosted gen4 applications- partially solved by jim's fuel mod, which adds extra lines to make sure fuel reaches the front rail and the injectors on there before the fuel is used up by the rear rail)

[djb2]

With a fuel return system the regulator works by releasing fuel from the end of the fuel rail to maintain pressure. This is conveniently close to the intake manifold, allowing the fuel rail pressure to be referenced to the intake manifold pressure rather than atmospheric or absolute pressure.

This is an advantage because the injectors have a constant pressure differential, and thus consistent flow rates. The computer doesn't have to go through additional calculations. Opening a injector for 10ms at high-vacuum idle releases the same amount of fuel as opening for 10ms while at low-vacuum operation e.g. WOT at low speeds.

[ekopel]

Is this benificial in N/A applications or low boost applications?

It seems beneficial in most applications, considering the better regulated fuel system will be able to deliver fuel to the injectors whenever they need it, but to what extent? It seems like a complicated modification for such a simple application (N/A or low boost).

[djb2]

A fuel return system referenced to the intake manifold is a good design. It does have costs.

The fuel pump is continuously pumping at high flow and pressure. It uses more electrical power, most of which is wasted. It's trivial compared to other engine losses, but comes into play when push starting or running with a failed alternator.

The fuel system is usually designed with full pressure from the tank pump to the injector fail. This completely eliminates the possibility of vapor lock (very common in the old days with engine-driven fuel pumps mounted on the hot engine block) but requires heavily reinforced fuel line for both the supply and return. Yes, even for the low-pressure return -- you don't want it to burst if the return path has a restriction.

[ekopel]

This has been a great thread, thanks everyone.