Wiring a dual pump setup in a single pump car

[Massive Lee]

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

[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?

[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]

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]

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]

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?

[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)