My little fuel pump(72) has been working for six years without a problem. Now that I am rebuilding the car and looked at the fuel hose diagram with fuel flows as per PP and DD, I must admit. I have not the foggest how this little pump works.
Fuel tank supply feeds a "Y" connector with the "R" port on the pump and the fuel line feeding the engine compartment. I do not see a valve in the "Y" connector.
Fuel returns from the engine compartment to enter the "S" port. Then the "D"port returns the fuel to the tank.
If the roller pump works by pushing fuel out the "R" port, why would the fuel not flow to the engine compartment and back to the tank via the supply line?
I have done a search and reviewed the classic section without finidng the answers.
What mechanism is being used?

Thanks,
L. McChesney
lamcchesney@netzero.net

Um.. the Y is only used on the R side (return from the engine and the tank)

S is suction from the large tank line/fuel filter

D is damper which is the pressure side and goes to the engine bay passenger side fuel rail and runs across the entire engine to the drivers side fuel rail. The system bleeds off what it doesnt need thru the pressure regulator which goes into the R side of the pump (Y).

Got it ?


B

Brad, that is the way I understood the system as well. But when I compare to the PP/DD FI hose diagram, it doesn't match up.

I think I have it now. The diagram confused me. The hoses on the top of the second diagram are from the fuel tank and not connecting with the engine compartment as it seems on the diagram. The hoses from the lower side of the diagram are entering and exiting the firewall.
I knew I didn't have it right.
Thanks again Brad.

L. McChesney

No problem.. when I come across some free time, I'll use REAL components and do a picture for the club site. Drawing's can be confusing.


B

S = "Saugen" == German for "suction"
D = "Druck" == German for "pressure"
R = "Rückkehr" == German for "return"

There is no damper, never has been. The 'D' simply means "pressure", as in "this is the port that supplies fuel at pressure". The Y fitting is in the return line, allowing any excess fuel from the pump to join the fuel that the fuel pressure regulator allows to go back to the tank.

Sorry about the drawing being confusing.

--DD

Thanks Guys,
No complaints DD. Now a question that I can't find in the manual, and I don't remember from when I pulled the system apart. The lines leading from the fuel tank, is the 9mm the feeding line to the "S" port of the pump and the 7mm is for the return?

I'm the one attempting to plumb a double pump system. The feed line from the tank is split to two filters, then to the "S" ports of each pump. The "D" ports feed seperate 3/8" fuel lines through the tunnel to seperate fuel rails/rales to the injectors. The rales/rails are combined to a common fuel regulator, which returns though the centeral tunnel to the tank compartment. Question now arrises. Upon entering the tank compartment, I split the return line into two which are to run to the "R" port of the pumps. Do I need to tee the return line at both pumps or just use a common tee?

Thanks
L. McChesney

Dave, did you turn arroung in the avitar?

9mm feed line, 7mm return.

If you mean was I looking away from the camera when the avatar pic was taken, yes. Check the thread about the Santa Clara breakfast from last week, you'll see the full-size version.

--DD

I like to think of S as "supply", D as "delivery", and R as "return". Easy to remember that way.

Teeing both the "R" lines from the pumps into the line returning from the regulator to the tank is the right thing to do, unless you want to make additional fittings on the tank.

I question the sense of sucking with two pumps through a single 3/8" fitting on the tank, as well as returning most of the fuel from both pumps and the excess from the fuel rail through a single 5/16" fitting.

Thanks all,
Chris, the duel pump is for stable pressure, but will not significantly increase flow. The fuel rails are much larger capacity as well. The theory is that the injected volume being much less than than the rail volume, thus decreasing pressure drop. Theory for now. Thus, there would not be an increased flow rates therefore, same sized feed/return line would not effect flow rates.
Thanks,
L. McChesney

L.,
Twice the pumps equals twice the volume. There is no feedback loop to tell the pumps they don't need to pump continuously. The fuel pumps will both bypass all the fuel they don't send through the injection rails and it will have to go back to the tank through the "return" line. While the amount of fuel flowing through the injection system may not increase greatly, the amount exiting and re-entering the tank will roughly double from the stock configuration. I am concerned that a pressure drop or backpressure at the tank fittings will negatively influence the gains you hope to achieve by running two pumps. It doesn't matter how big the injection rails are. The point of greatest restriction will be at or near the tank.

I got the test run of the dual pump dual fuel runner circuit done and it looks great.
The engine is not in as yet so I hooked up the circuit and powered it directly from a 12V source. I triggered the injectors using a 3V battery supply. Adjusted the rale pressure to 40psi.
Triggered a injector and pressure rock solid at 40psi.

To review the system:
Feed line 5/16 from the tank, through filter, split to two Bosch 0580463009 pumps in the front trunk. Two seperate (D)delivery lines via 5/16 metal fuel lines through center tunnel to engine firewall. Each fuel line via 5/16 hose to a fuel rale created from 3/8" brass fittings with 3/8 hose feeds to injectors and a "Tee" for pressure gauge and cold start.
The rales are "Y"ed together to enter the single fuel regulator. The fuel regulator feeds a 5/16 return line through the center tunnel to front trunk. There return is split to the two pumps "R" and "T"ed to fuel tank.
It took a couple minutes to get up to pressure and one injector leaked for a while but then stabilized.
The spray cone from the injectors looks good. Have not measured flow yet, next project.
Any advice on cleaning/rebuilding the injectors?

Thanks all,
L. McChesney