Vicl

Hello, Mishar!
Here is my understanding how it works, based on the previous research:
When the ignition is turned on (“terminal 15 on”), the Transfer Fuel Pump G23 forces a maximum volume of fuel to the pressure regulator at the fuel rail to achieve short starting times. The Fuel Pump G6 also routes fuel to the pressure regulator, as well as into the pipes for the two suction jet pumps in the side tank compartments. Each suction jet pump conveys fuel from the chamber on one side across the tank to the reservoir in the pump in the chamber on the opposite side of the tank. Pressure Regulator (58 psi; 400 kPa; 4 bar) This pipe routing prevents dry running of a pump in critical driving situations such as cornering or if the vehicle is at an
extreme angle. The return pipe is shared by both fuel pump reservoirs. If one fuel pump reservoir is full, the pipe is closed by a check valve and the entire return volume runs into the second fuel pump reservoir. If both reservoirs are full, the check valves are overridden and the excess return fuel runs into the tank.

Two-Stage Fuel Pumps Transfer Fuel Pump G23 and Fuel Pump G6 are both of the two-stage flow type. Both fuel pumps work the same way. In the first pumping stage, the pre-stage pump draws in fuel from the bottom of the tank and conveys it into the pump reservoir. This ensures that even small residual quantities can be transported. In the Return second pumping stage, the main stage pump draws fuel from the pump reservoir and routes it to the fuel pressure regulator
at the fuel rail. The fuel pump assemblies rest on and are clipped to the bottom of the tank. Flanged covers provide access to the components.
G23 is the passenger side pump and it is constantly running. G6 is a driver side pump. It runs at start, then it will run each time when you need to transfer the fuel from the driver side of the tank and when the engine is greater than 3000 RPM. In other words it exactly matches the DA8 observations.
In his case G23 was not working. He starts the engine. G23 and G6 should start (in his case only G6 was working). Then G6 stops and the engine die. Why G6 starts for few seconds after – I do not know. Maybe it knows the pressure is low and it adds up a little bit.
But G23 is definitely a main pump that is running all the time. Also, theoretically you can rewire and drive only on G6 pipe. I never explored that option.

05SilverA8

This might actually work and would prevent being stranded and being held for ransom by the dealer. If I have time today I will test this.

mishar

Generally yes. I've red that text few times. Just G6 (left) pump has nothing to do with fuel transfer, except transferring it from the tank to its own small container utilizing its prime stage. Transferring fuel from side to side is under G23 (right) pump control.

mishar

I was to do so, but as you volunteered...

PaulW

www.volkspage.net/technik/ssp/ssp/SSP_282_d1.pdf

mishar

Yes. Same link above. Problem is in translation. Person doing it has to understand functionality and that's not always the case. Simple mistakes are possible too. I think there are a few in this SSP 282.

ezveedub

The SSP for how the fuel pumps works is incorrect. In short, the right side fuel pump runs all the time, while the left side fuel pump runs at start up and under load. When the right side pump is failing, the car will start off the left pump, then stall out when the ECM turns off the pump shortly after start up. A simple test is to remove the left side fuel pump relay from the relay carrier by the battery in the trunk. This way, you can test the right side fuel pump alone. With a fuel pressure gauge installed, you can see if the right side pump is working properly or not. In some cases, its dead or putting out erratic fuel pressure.

If you look at the MVBs in the ECM (can't remember them right now) you will see the values for both fuel pump on/off activation and you can watch when the ECM turns the left side fuel pump on and off during start up, idle and while applying throttle.

mishar

Yes. That's exactly what I finally figured out. Only edition is that right pump is also powering suction transfer pumps.

Would rewiring right pump + wire to the left pump bring us home?

ezveedub

If you did that, it would draw more from the fuel pump relay and fuse. The relay is already powering up the fuel pump, coils, mass air flow meter, N80 valve and I think injectors (don't quote me on all those circuits, its been a while). I know you get like 18 or 19 DTC codes with a bad fuel pump relay. If you did a rewire, it would be the triggering wire from the ECM to the relay for the right side pump to the relay in the trunk for the left side pump. This way you trigger the actual circuit properly without overloading the relay with a direct rewire off the pump itself. Not sure if doing this will cause a DTC in the ECM. It may monitor the relay circuits and see constant power when it should be off.

Any reason you're trying to keep the left side pump on all time like the right side??

mishar

Yes, actually a very good reason: dead right pump. By rewiring I meant unplugging both pumps and plugging right pump wire with some extension to the left pump. Just to get home.