Fuel Flow Diagram / Regulator Screen

[Crossthreaded Nut]

Hey guy's, I stumbled upon this fuel flow diagram for our trucks and I have a question. Look at the fuel system schematic on the link.

http://www.nav-international.com.br/frame_master.asp?tipo=powerStroke&pg=manual_i/powerStroke/hs.asp

According to the diagram, the screen at the fuel filter bowl / pressure regulator that we all like to clean, only screens the big chunks before returning fuel to the fuel tank. I'm sure that I feel the "seat of the pants" horsepower-o-meter go up a couple of notches each time I clean that screen.

Does anybody know if this diagram is correct?

Thanks,

James

 

[95_stroker]

James,

If I follow and understand that diagram correctly, the low pressure side of the pump lifts the fuel out of the tank and pushes it through the filter, then it hits the high pressure side of the pump and on to the fuel rails for use at the injectors, what isnt used is returned through the regulator and some of the fuel can pass through an orifice and screen (the one we clean) back into the filter cannister to help keep the low pressure side of the system flooded so to speak, what isnt passed back into the system returns to the tank. I have also heard that what we clean off that screen is in fact injector o-ring material???? I have no data to back that up, just what I have read.

Mike

 

[Crossthreaded Nut]

What I thought was interesting is that the screen is not blocking fuel flow to the injectors.

 

[95_stroker]

What I thought was interesting is that the screen is not blocking fuel flow to the injectors.

Correct, it is not blocking flow to the injectors, but what it is doing is slightly lowering the pressure on the low side by not allowing any left over high pressure fuel into the low pressure side which in turn lowers the pressure on the high side. Essentially it is making your lift pump work quite alot harder.

 

[MUDWHISTLE]

I get it so by being plugged it does not contribute to the amount of fuel on the return side in turn allow less back pressure and lowering the fuel pressure to the injectors. I have cleaned mine about every eightteen thousand miles since I found out about this and everytime it is plugged. But hey what do I know

 

[95_stroker]

The way I look at it is this; when the screen is plugged it turns your fuel pump into a low pressure fuel circulation pump, with the screen clean, it allows high pressure fuel to spill back into the low pressure side thus meaning the pump can act as a pressure pump and not so much as a circ pump.

 

[MUDWHISTLE]

Creating less of a pressure drop on the FPR, Right?

 

[95_stroker]

Creating less of a pressure drop on the FPR, Right?

Hmmm, yes it should. Never thought of that aspect of it.

 

[JOAT]

The IH housing is either different or that schematic is wrong. Our filter housing has the low pressure side of the FPR (return) connected to the passage from the clean side of the fuel filter so fuel recirculates. In the picture if you connect the output from the FPR to the line from the bottom of the filter, you get how ours is plumbed. This allows a low volume of fuel thru the filter and minimal heating of the tank. Other schematics I have seen show the fuel path with the unused fuel recirculating, and inspection of the housing shows this is so.

The screen we clean is for a metered return to the tank. Also any air that collects is purged back to the tank. If the screen clogs, then air can build up and get into the high pressure side.

The fuel passage after the FPR and the fuel passage on the clean side of the filter are connected so unburned fuel recirculates in the high pressure/FPR loop. There really should be no return of fuel from the FPR to the housing, as the pre-filter pressure should be equal or greater depending on the filter condition. Some fuel can return to the tank from the FPR side as well as from the bowl screen.

IMO "FPR screen" is a misleading name. It really has nothing to do with the FPR function and is merely a purge/return orifice screen. If memory serves the IH version of the filter housing has the screen separate from the FPR but function is the same.

I edited the schematic to be like ours. The oval in the line is the filter screen or mesh inside the FPR itself.
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