Stock Fuel System Diagram (Is this correct?)

[Shane2GSX]

I'm trying to get a grasp on how the stock fuel system works with an FPR. Soon I will be getting a Walboro 255 pump, 780cc injectors and I will need an FPR to go with them. Can someone tell me if this diagram is correct?? If it is correct, how does the FPR regulate the fuel pressure when it is on the return line?? It makes more sense to me that it should be on the feed line before the fuel hits the rail.

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It makes more sense to me that it would look like this:

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[playitlouddsm]

Fuel system goes from Tank>FPR>Fuel rail inlet>fuel rail outlet>Fuel filter>back to tank.
-Nick

 

[Stanford]

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Here, I just made this in paint because I am bored at work. It should help, as yours are both wrong and have lines I have never seen.

The FPR goes on the end of the fuel rail. It controls pressure by bypassing a certain amount of fuel. At idle with vac line connected it will be letting loads of fuel go by so the fuel pressure is low. Under boost it holds the fuel in more, therefore increasing pressure with boost. This is an elementary way of explaining it, hopefully you get it now.

Ok the pic is being lame, but it goes from Pump, Filter, Rail, FPR, Return, Tank.

 

[Shane2GSX]

Haha. I get the way you are explaining it, but I just can't see your diagram, can you blow it up some?

 

[VelocitàPaola]

Whoa... way to jack my diagrams.

This is the original diagram I had made (there are variatrions out there for FMU, AFPR, etc.). It's a schematic showing how everything comes stock on 420A cars. The early fuel system style (95-96) is most like the 4G63 set up.

 

[Shane2GSX]

Okay, I think I have it. I guess what it comes down to after looking at all the diagrams, is that it doesn't matter where exactly the FPR is on the stream of the fuel, it's all about relieving pressure, which it can do at any point.

VelocitàPaola:
Yeah, I got it off another post of yours.

Thanks to all for the fast answers..

 

[travislaw]

Not to get off topic here, but why would the fuel filter be after the fuel rail in the late 96+ cars? I thought the whole point of the fuel filter was to keep the crap floating around in your gas tank from getting in the engine. If it is after the fuel rail on the return line side, how is it keeping crap out of the engine ?

 

[Stanford]

Okay, I think I have it. I guess what it comes down to after looking at all the diagrams, is that it doesn't matter where exactly the FPR is on the stream of the fuel, it's all about relieving pressure, which it can do at any point.

VelocitàPaola:
Yeah, I got it off another post of yours.

Thanks to all for the fast answers..

No. It needs to be after the rail. It can be mounted right to the rail or on the firewall via a length of braided hose.

 

[Shane2GSX]

No. It needs to be after the rail. It can be mounted right to the rail or on the firewall via a length of braided hose.

It's not after the rail on VelocitàPaola's first diagram.

Stanford, can you explain why it needs to be after the rail?

 

[Shane2GSX]

Not to get off topic here, but why would the fuel filter be after the fuel rail in the late 96+ cars? I thought the whole point of the fuel filter was to keep the crap floating around in your gas tank from getting in the engine. If it is after the fuel rail on the return line side, how is it keeping crap out of the engine ?

Good question, I'd like to know this as well. Makes no sense to me... WTF

 

[VelocitàPaola]

There's too much confusion here.

Stanford was talking about the FPR. The FPR isn't about relieving pressure, it's about building pressure; this is why it's either mounted directly on the fuel rail or after the fuel rail. It's a pressure-sensitve diaphragm that restricts fuel in order to increase fuel pressures. Higher fuel pressures, in turn, mean greater fuel flowing from the injectors.

As for the fuel filter; it doesn't matter where it's located. There is a basic mesh filter on the fuel pump to get rid of any large contaminants. The fuel filter itself keeps the fuel in the tank clean. It's a continuous recirculation process (hence the return fuel line), so as long as the filter is somewhere in the fuel line circuit, it'll do its job just fine.

 

[Shane2GSX]

There's too much confusion here.

Stanford was talking about the FPR. The FPR isn't about relieving pressure, it's about building pressure; this is why it's either mounted directly on the fuel rail or after the fuel rail. It's a pressure-sensitve diaphragm that restricts fuel in order to increase fuel pressures. Higher fuel pressures, in turn, mean greater fuel flowing from the injectors.

Okay, that makes sense. So when the diaphram is being pressed down by pressure, it causes more restriction, raising fuel pressure. When the diaphram is pressed down less or not at all, there is less restriction, less fuel pressure.

As for the fuel filter; it doesn't matter where it's located. There is a basic mesh filter on the fuel pump to get rid of any large contaminants. The fuel filter itself keeps the fuel in the tank clean. It's a continuous recirculation process (hence the return fuel line), so as long as the filter is somewhere in the fuel line circuit, it'll do its job just fine.

Makse sense as well. Thanks for all the great info.

 

[99gst_racer]

As for the fuel filter; it doesn't matter where it's located. There is a basic mesh filter on the fuel pump to get rid of any large contaminants. The fuel filter itself keeps the fuel in the tank clean. It's a continuous recirculation process (hence the return fuel line), so as long as the filter is somewhere in the fuel line circuit, it'll do its job just fine.

Just a small addition/correction. It is somewhat relevant where the fuel filter is located. It must be between the fuel pump and injectors/fuel rail. A 10 micron filter is recommended. The filter on the pump is a pre-filter and is more coarse that the primary fuel filter. The purpose of the 10 micron primary filter is to filter the fuel to keep from clogging/contaminating the fuel injectors.


Also, I'd like to mention that Stanford's diagram in post #3 is correct for the 4G63 engine.

 

[Siral3x]

The fuel filter for most European cars is always mounted between the fuel pump and injectors/fuel rail, and some diesel engine like:TDI VW etc, etc have 2 of them ,1 on the return line just because the excessive moisture in the gas. And belive me you don't want to wake up at 6am and crank your diesel 40 min to start , so you can go to work it in the winter
The injectors nozzle will clogg 10x more in a sistem without a fuel filter on the feed line.
As far as I know about the FPR it can be mounted anywhere after the fuel rail..but the car manuf. make it easy and put it in the engine bay
And yeah...on my 2g 4g63 the FPR has vaccum line to that goes to the vaccum boost source..i don't know abt 1G but I think it's the same..ohh..i guess 99gst_racer already made that clear

 

[VelocitàPaola]

Okay, that makes sense. So when the diaphram is being pressed down by pressure, it causes more restriction, raising fuel pressure. When the diaphram is pressed down less or not at all, there is less restriction, less fuel pressure.

Something like that. I've never taken one apart... but I think its actual construction is a little more complex because it has to adjust fuel pressures under both boost and vacuum (coming on a factory turbo car).

 

[steve]

Just so it's clear, like Stanford's drawing the 4G63 fuel system is set up like this.
The 420a is different. At lease some of them are set up with the fuel filter, FPR and return line in the back with a single line running to the fuel rail.

Steve

 

[VelocitàPaola]

Thanks for clearing that up, Steve. I changed the original diagram to include the 4G63 (and fix something I noticed about one of the 420A set ups... ).