Fuel Pressure Regulators - Good or Bad?

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What's the go with return line?
The FPR is vacuum driven, which sounds like a cheap way of avoiding PID on the pump.

If you were to remove the FPR, block the return line, I suppose a static pressure sensor on the line would be needed and PID control to adjust the pump speed to suit.

Which then gets to my question: Would switching to a returnless fuel system deliver savings (or possibly consume fuel due to possible greater fuel pressures and therefore more fuel injected?)

[justme1969]

It has its own probblems that make it less than Ideal. Air bleed and vapor return.
Both do more than thier namesakes imply.
When you run out of fuel testing your new eco mod it would probbably require a mechanic or skills to get fuel into injectors again. fuel vapors would bypass thier basic systems and free vent into possibly the intake but if a cars not running this vapor would in effect be like a bomb in waiting. Might help start up in winter though lol.
Un less you were talking about a diesel???

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Not talking about a diesel.

Ahh, I get that if you run out of fuel, the air in the line would prevent fuel / make for hard starting.

But that would clear would it not? Injector opens, air goes into engine, repeat, repeat, fuel reaches injectors.

Vapors are controlled by the EVAP emissions already (which a return and returnless system both have). It wouldn't be a bomb as the vapours would still vent (through EVAP to atmosphere apparently).

[UFO]

I do not understand why you think a vacuum reference and a return line is not a well designed fuel supply. The vacuum reference ensures a constant pressure differential across the injector for all manifold pressures so the duty cycle applied results in consistent fuel delivery. The return line ensures the fuel stays cool and vapor-free for all operating conditions. It is simple, but not too simple, to paraphrase Einstein.

[t vago]

Returnless fuel systems are mainly there to prevent evaporative fuel emissions. Evaporated unburnt fuel is a component of air pollution.

There are two different styles of returnless fuel systems being made right now.

One, produced by Ford and Kia (and perhaps others, I don't know) uses a fuel pressure sensor and varying the drive duty cycle to the electric fuel pump to maintain a fuel pressure that is indexed to manifold vacuum. The fuel injectors would see a constant differential fuel pressure across them, regardless of intake vacuum. This fuel system would use the PID (proportional-integral-differential) control system algorithm that OP is mentioning.

The other is produced by Chrysler. It uses a traditional relay to control power to the fuel pump, and a fuel pressure regulator that has no vacuum port. That fuel system maintains a pressure that is a constant gauge pressure of 58 psig (49.5 psig on older models). Of course, this results in variable differential fuel pressure across the fuel injectors. Chrysler engine computers take this differential pressure into account when calculating injector open times. Thus, it is not necessary to develop any sort of control algorithm for the fuel pump.

[Occasionally6]

For a DIY mod I see no real reason not to drop the pump speed (and flow) down when the fuel demand is low but keep the manifold vacuum referenced regulation as the final determinant of fuel pressure. i.e. reduce the amount of fuel being returned to the tank.

In a naturally aspirated i.e. non-supercharged engine, maybe a MAP sensor input (0-5V)into a solid state relay configured as an op-amp?

I'm not sure that there is much potential to save electrical power but it would be an interesting project to do for the fun of it.

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That won't be the case though, with the return unchanged, all will happen is the pressure differential will drop and so the injectors will flow less.. return line still less resistance than the restriction though the injectors.

The only way it will work I think is to go all the way to a return less system - or dropping pump speed minor amounts. There'll be some savings in the pump speed somewhere - it's a continuous drain to maintain the pressure it does.

[Occasionally6]

It will work if you keep the inlet pressure to the fuel rail higher than the bleed off pressure at the regulator. That way the fuel pressure is still set by the fuel pressure regulator rather than the pump output. The only change is that less fuel is required to be bled back to the tank in order to maintain the lower pressure in the rail.

There's not all that much to be gained though. A fuel pump might draw 7 amps at 14V so just under 100W.

You might try to use the pump input power to control the fuel pressure without using the mechanical regulator but the relationship between pump input power and fuel pressure is non-linear. That means it would be necessary to map the input power to pump output vs manifold pressure. It's a lot easier not to have to do that, leave the mechanical regulation in place, and accept that the pump will run a bit harder than strictly necessary.