Wiring a dual pump setup in a single pump car

[mayhem]

I think another Spece30 thread answered my question. From a dual in tank pump discussion, but I can apply it still. Again jlevie and spec crew with the data. http://spece30.com/forum/16-general-...it=10&start=40

My fuel flow with accumulator/big swirl pot:
LP pump(w/capped return) > swirl pot
Swirl pot > 044 > filter > fuel rail
Rail return > swirl pot
Swirl pot return > stock tank return
Swirl pot overflow > tank (have to find this on tank. Seems like it could be same as return)

[mayhem]

Jlevie, thank you. I found another of your helpful posts on SpecE30.

http://spece30.com/forum/43-fuel-system/45497-gas-tanks-fuel-pumps-and-fuel-starvation-s?limit=10&start=20#57315

As you know it's a circus act getting to the pump in a caged car. I need to confirm but I believe my stock pump only had one fitting which means the return is routed else where. That makes me wonder how fuel from the other side of the saddle makes it over. In regards to the 2 port transfer pumps could i cap the pump return port and route my surge tank return back to wherever the heck the return in the tank is now?

[jlevie]

Bingo! I assume the pre 87 in tank pumps were low pressure and would do the trick. Do the pre 87 in tank pumps have the same # of inlets/outlets as the big tank post 89's?

The early in tank transfer pump does have an output and return fitting like the late in-tank high pressure pump. But you will have to use adapters to account for the difference in line sizes.

[mayhem]

You would really want to swap the in-tank high pressure pump for a low pressure transfer pump. When the pump starves it isn't immersed in gas, which is bad for a high pressure pump (the fuel cools it). Low pressure pumps aren't as sensitive to cooling. The pumps get wired in parallel.

Bingo! I assume the pre 87 in tank pumps were low pressure and would do the trick. Do the pre 87 in tank pumps have the same # of inlets/outlets as the big tank post 89's?

[jlevie]

You would really want to swap the in-tank high pressure pump for a low pressure transfer pump. When the pump starves it isn't immersed in gas, which is bad for a high pressure pump (the fuel cools it). Low pressure pumps aren't as sensitive to cooling. The pumps get wired in parallel.

[mayhem]

Back from the dead, but related question. My 89 325i suffers from starvation in right hand sweepers like so many others. It's a single pump system and I want to add in a surge tank. This thread gets me on the right path, but confirm or shoot me down here:

1) In tank pump can be OEM high pressure pump or does it need to be swapped for a low pressure unit?
2) The two pumps can be wired in parallel?

[Massive Lee]

Let's celebrate. JoshH has posted outside of the P&R cave. Welcome to the "outside" world...

[joshh]

Damn good thread. Thanks for the info Lee...as much as I hate to say it, you are quite useful after all.

[Jean]

Lee - thanks!

[jlevie]

I run Enduros in my Spec E30 and being able to run the car down to fumes is an advantage. When using a 63L tank there are two viable solutions that will achieve that goal. One is to install a transfer pump in the left side and use it to feed fuel to the high pressure pump in the right side (what I have in my car right now). The other solution, that is probably more applicable in this situation, is to use a transfer pump on both sides, feed their output to a surge tank, and use an external high pressure pump to feed the engine.

[Massive Lee]

[Jean]

There is already a fuel return line going to the tank via the low pressure fuel pump housing, so it can be re-used yes?

So, 1 going from the low pressure pump to the rest
1 going from the rest to the high pressure pump

1 going from the res to the low pressure pump housing/fuel return line
1 going to the res from the fuel return line?

Ok, 3 lines are fine and one needs to be added it sounds like. Why 2 return lines?

[Massive Lee]

4 lines required. You also need fuel return to the tank

[Jean]

I didn't know you had to run all these additional lines, thought there needed to be a res with some fuel between the two filters and you are good.

So you need atleast 3 lines, one from the low pressure pump to the res, one from the res to the high pressure pump and the fuel return line routed to the res instead of the stock low pressure pump housing?

[Massive Lee]

Hi Jean

I suppose that "res." means surge tank. Right?

It can work with two lines, just like a simle fuel filter canister, but you won't recuperate return fuel from the injector rail though, and the surge tank will empty itself pretty quick. Basically it'll be good only for a couple of seconds.