Audi TTRS - Duel fuel pump control strategy

Good day

I'm working on my 2021 Audi TTRS project car and need assistance with the planned fuelling upgrade.

Running Unitronic Stage 2 ECU and TCU software with associated hardware mods and E85 fuel.

Use the car on track and struggle with fuel starvation due to the lateral g-forces.

So plan to get a Radium fuel surge tank (FST) installed with a high volume E5LM pump.

The OE LPFP will then act as lift pump for the FST; effectively running in series.

My challenge is to get the control strategy correct for this application, while still using the unaltered Unitronic files..?

What I know for certain;

The E5LM and OE fuel pump are brushless and can be controlled with the OE J538 pump controller (PWM).

This is done by IROZ Motorsport who modify the OE LPFP with the E5LM pumps and use the J538 controller for this, without any custom tuning on the ECU required.

The mechanical fitment and fuel plumbing is sorted and know what to do with that.

The unique situation is to use the ECU signal to control both pumps.

One way I considered is to running two J538 controller, one for each pump, but driven with the same ECU pulse/signal wire...

Alternatively, and probably the better strategy, it to control the new FST pump with the existing J538 controller and the ECU signal.

Then find a way to control the OE LPFP (lift pump) in a way to only make sure the surge tank is always filled.

The surge tank will simply drain any excess fuel back to the main tank.

The objective is to ensure the fuelling system functions reliably, but also economically. Hence to avoid pumping fuel unnecessarily and create heat in the fuel and extra electrical consumption.

Assistance in this regard will be greatly appreciated!

You've definitely got a tricky one there and I can't add personal experience given that i haven't tried this myself previously. For complete simnplicity I'd actually consider switching the stock LPFP to a brush-style pump and just run it continuous. This would obviously eliminate any complexities with control. The next best choice would most likley to splice the control signal to two separate controllers but I can't say with certainty this will work.