Has we ever discussed the RS6's fuel pump configuration, theory, etc.?

[SteveKen]

I'm doing some comparisons to the non-RS6 4.2 single in-tank pump fueling and the RS6's internal and external/transfer pump?

First off, I'm wondering if the actual pumps that are part of the in-tank assemblies are different between these items:

4B0906087BF (RS6)
4B0906087P (non-RS6 4.2)

After this pump, the RS6 also has a transfer pump (P/N 4B0906089A) that's external to the tank.

From what I can tell, the pumps are in series with the in-tank pump feeding the external pump then through the filter up to the FPR.

Wouldn't the second pump either starve the first pump or cause back pressure to cause premature failure?

Not sure if it's ever been discussed here, but I'm guessing that these pumps have to be matched pretty well in order to not wear out prematurely. With that said, am I asking for trouble if I want to change one of these out to something else or just use one alternative pump?

Adding another monkey wrench to this is that they are both normally running at 10V except when certain conditions make them run at 12V. From what I can tell, both pumps are always at the same voltage, though.

[Brav]

Interesting topic. All I know is that when my fuel light comes on, the pump goes to MAX voltage and gets quite loud, instantly. It should only go to high voltage at or near WOT. If you listen carefully, you can test this yourself, as you can barely hear it as it comes off throttle, then goes quiet. But yes, one more thing to not quite work to spec, then kill itself.

[SteveKen]

I thought someone also mentioned that it's at 12V on start-up.

Initially, since the OEM transfer (in-line) pump is like $900 from the dealer, I though it might actually be a surge tank, but the way it's plumbed doesn't suggest that.

I'd like to actually convert the system to a single in-tank pump (need to learn what the sufficient specs need to be) or use the existing in-tank pump (provided the specs on the pump, itself, are sufficient) to feed a surge tank.

[Zmey]

Interesting topic. I always wondered about the same thing. Running bigger injectors(72cc) and dual Bosch 044 pumps one in tank and one external all for e85 setup haha jk. I want to know how much lph (liters per hour)the current setup on the rs6 provides, and go from there. as long as you can get a single pump that can flow as much or more lph than stock, i dont see why it cant be converted to a single fuel pump.

Edit: found this interesting read http://www.rs6.com/showthread.php/24595-external-transfer-fuel-pump-on-my-RS6-died-after-68k-miles-any-suggestions

[SteveKen]

The link in the linked thread above has the in-line pump at 255 lph.

Do the lph specs use a nominal tube ID, too, as this would affect that number. I'm guessing that there are in line flow meters that can be used to calculate this, but the only on es I can find use 1 - 1.5" ID hose and are $900, so not optimal for automotive applications in many aspects.

Maybe I can hotwire the pumps to a switch and external power supply with 10V and 12V and time them while filling some beakers.

Radium Engineering has some good information and products, too, it seems. http://radiumauto.com (http://radiumauto.com/)

Also, where's the thread with the guy who bought speedtrapped's car ans had to replace the fuel pump and clean the injectors, etc. Wasn't there some specs of the in-tank fuel pump in that thread?

[Zmey]

I changed fuel pump on my b5 s4 from stock to 044 Bosch and i didnt have to modify the existing fuel lines, just had to purchase a basket from a8 where the pump can sit. i think ID of 1" is a lil big for fuel pump/fuel line there is a lot of AN adapters to make it work if the inner diameters dont match.

[ttboost]

http://www.rs6.com/showthread.php/24829-Remember-Special-Sauce?highlight=

[DHall1]

Steve,

Having enough fuel is so over rated. Dont you think? ;)

You could perform a bench test at the full rated voltage to both RS6 pumps then go on the hunt for the proper intank units. Take a fuel line off at the engine and plum something down to a gallon bucket. Time the test to fill the gallon and extrapolate from there.

A beaker may be too small to extrapolate without a large margin of error.

What is the default pressure of the RS6 fuel pressure regulator? You would need to draw the sample after regulator that way to could get the pressure in the calculation.


The link in the linked thread above has the in-line pump at 255 lph.

Do the lph specs use a nominal tube ID, too, as this would affect that number. I'm guessing that there are in line flow meters that can be used to calculate this, but the only on es I can find use 1 - 1.5" ID hose and are $900, so not optimal for automotive applications in many aspects.

Maybe I can hotwire the pumps to a switch and external power supply with 10V and 12V and time them while filling some beakers.

Radium Engineering has some good information and products, too, it seems. http://radiumauto.com (http://radiumauto.com/)

Also, where's the thread with the guy who bought speedtrapped's car ans had to replace the fuel pump and clean the injectors, etc. Wasn't there some specs of the in-tank fuel pump in that thread?

[ttboost]

I seem to recall the RS6 having 3.8bar or 4bar FPR? Thinking the former...

[V8weight]

I seem to recall the RS6 having 3.8bar or 4bar FPR? Thinking the former...
4 bar...

[ttboost]

4 bar...


..or the latter...

[SteveKen]

You could perform a bench test at the full rated voltage to both RS6 pumps then go on the hunt for the proper intank units. Take a fuel line off at the engine and plum something down to a gallon bucket. Time the test to fill the gallon and extrapolate from there.


I think you see what my ulterior motive is here.

I need to know whether the stock S6 fuel pump and delivery will be sufficient for supplying the RS6 lump.

I've got an S6 tank, lines, fuel pump w/ constant 12V, etc. and there's nothing in common with the RS6 unless the difference in P/N's is code for the flagship tax.

[KWest]

From what I can tell, the pumps are in series with the in-tank pump feeding the external pump then through the filter up to the FPR.


Wouldn't the second pump either starve the first pump or cause back pressure to cause premature failure?



Having learn all about fuel system last summer helping a friend build 700+ WHP CTS-V.


The in-tank pump (feeder) is a low/no pressure supply, its sole job is to supply the external pump (pressure) with the fuel it needs to supply the fuel rail.


The internal pump supplies the external pump with (0bar) of fuel pressure, and XXXX LPH.
The external pump supplies the fuel rail with 4+ bar of pressure, and XX LPH.


Positive displacement pumps need a restriction to create pressure. Since the there is no restriction across the external fuel pump (when its on) the in-tank pump is creating no pressure, just flow.
Head end also affects a pumps output, the all specs are given with 0ft head end. So because our external pump is being supplied with all the fuel it can drink from the in-tank pump it's head end is 0ft.


There is such a thing as too much fuel flow when it comes to fuel systems. Every time a drop of fuel is compressed it is heated, if you are flowing 500 LPH and the demand is only 100 LPH then 400LPH is being compressed (heated) for nothing. Hot fuel is bad.

[KWest]

To add to the above post. Here is a great link with a ton of fuel pump info http://www.stealth316.com/2-fuelpumpguide.htm

You can see in the graphs that a few extra volts makes a sizable difference in output. I would assume that Audi limits pump voltage when the requested lambda = 1 to prevent heating the fuel and/or to minimize the return line size for cost purposes.


Steve,
If you keep the external pump and the S6 pump has enough flow at 0 pressure (which it should) then you shouldn't have a problem.

PS. Does the edit post expire on this board?

[SteveKen]

To add to the above post. Here is a great link with a ton of fuel pump info http://www.stealth316.com/2-fuelpumpguide.htm

You can see in the graphs that a few extra volts makes a sizable difference in output. I would assume that Audi limits pump voltage when the requested lambda = 1 to prevent heating the fuel and/or to minimize the return line size for cost purposes.


Steve,
If you keep the external pump and the S6 pump has enough flow at 0 pressure (which it should) then you shouldn't have a problem.

PS. Does the edit post expire on this board?

Thanks for the link.

The S6 pump has enough flow and pressure to supply the NA 4.2. If I add an external inline pump to this, I might be taxing the in-tank pump because I'm guessing it's not a low pressure hi volume pump as you say the RS6's in tank pump has. If I could find a suitable pump to swap out the in-tank pump, and then add the external pump, this should be enough to mimic what's going on in the stock setup.

In the end, I'm not planning on going any further than stage 1, so ...

[SteveKen]

See Item 19 in this picture. ETKA calls it a 'junction'. Different part number between the S6 and the RS6, too. Initial thought is that it was part of the fuel return system but could this be a regulator to relieve excess pressure to make the in-tank pump a '0 pressure' pump?

http://becost.ru/vag/img/manufactur/audi/id/020151262

[hahnmgh63]

Does the junction piece just distribute the returned fuel to both sides of the fuel tank? If so that could be a difference in the S6 fuel tank compared to the RS6 tank? When I dropped a Motronic 3.6ltr motor with approx 290bhp into my '74 911 RS clone that originally had a 2.7ltr 150bhp motor I was able to use the same fuel pump and all has been fine for over 4yrs now, a bit of track time on it without any fuel starvation. Those two engines are over 15yrs apart as well as the fuel pumps they came with. I think the Bosch pumps supply a good margin, much of the design changes are for fitment. I wouldn't worry about it yet, I would just give it a go and change it later if needed.

[KWest]

The junction (19) looks to be on the supply side, it's tough to say thou. On the CTS-V there is a similar suction jet, when fuel from the feed pump flows thru the jet it pulls fuel from the non-pump side of the tank. That way both sides empty once the fuel level has dropped below the point that they will gravity transfer.

It looks like the return is feed back into the fuel bucket.

Steve,
If the S6 pump can supply 300+ hp at pressure, it will be fine as a feeder pump. To be safe i'd have fuel pressure gauge in the car, even if its only for testing.

The problem my friend had was no matter what config the pumps where in, under load the fuel pressure would drop. It turned out that the feed pump was sucking the fuel bucket dry. Once a surge tank was installed he was able to get rid of one of the pressure pumps and both Kenny Bell Boost-A-Pumps. Now it's a Denso in-tank to a Bosch 044 in a surge tank, the return line passes thru the surge and then the surge returns to the tank. That's enough for 700+WHP on a mustang dyno.

[buster0984]

Steve,

i breifly read down through the thread and didn't see this so i figured i would throw it out there.

"if" the a6/s6 and the rs6 share the same or similar tank configuation i believe that the 044 internal pumps will not fit due to being to tall, the largest you can fit i believe in an internal 040 which from what i remember off the top of my head is only good for around 500 ish horsepower or so.

if you are looking to run a different pump and avoid the $900 dealer price tag, i'm sure you could make the Aeromotive A1000 High Flow Pump (for example) work and that pump is capable of supporting 1000 hp on turbo fuel injected cars (this is all assuming that that piece is indeed an aux/second pump outside the tank) and you can get them for ~$350 new.

just some thoughts.

[KWest]

Steve,
if you are looking to run a different pump and avoid the $900 dealer price tag, i'm sure you could make the Aeromotive A1000 High Flow Pump (for example) work and that pump is capable of supporting 1000 hp on turbo fuel injected cars (this is all assuming that that piece is indeed an aux/second pump outside the tank) and you can get them for ~$350 new.

just some thoughts.

The Aeromotive A1000 will only support 1000hp if the fuel supply is higher than the pump, so effectively 0ft head. If it is required to pull fuel from the tank its output drops substantially. This is true for any positive displacement pump. Also the 1000hp is at 20psi fuel pressure, at 4bar it will support 700hp, now add 15psi of boost with the stock 4bar regulator will require 5bar of fuel pressure. At 5 bar the A1000 supports 550ish.


With a return system, the base pressure is set with the engine off, but the pump running. For a GM, this pressure is usually set to 58psi (factory fuel pressure in the rail). The vacuum/boost referenced regulator will help to change the pressure in the rail based on the pressure in the manifold. When an engine is idling, it may be pulling 20 inHg of vacuum, which translates to roughly 10psi. The reference to the regulator will allow it to adjust and lower the pressure in the rail to 48psi, resulting in 58psi effective pressure, which is the same as the base pressure. When the engine is making 10psi boost, the regulator will adjust and increase rail pressure to 68psi, again resulting in 58psi of effective pressure. The regulator will constantly bleed off pressure inside of the rail to maintain the same effective pressure at all operating conditions. This helps to prevent a loss of effective pressure during wide open throttle, and also helps to prevent injectors from having to run extremely low pulse widths to fuel at idle. A downfall of return systems is the fact that they circulate fuel through a very hot engine bay, ultimately carrying that heat back into your fuel tank.

Steve,
I don't know your full plan but if your looking for a replacement to the external pump IMO your best options would be something like the 034 surge tank or similar. You won't save a ton of money, however your fuel system will never be a worry.

http://www.034motorsport.com/fuel-injection-solutions-fuel-pumps-fully-enclosed-fp34-044-fuel-surge-tank-p-21527.html

[Korben007]

i plan on running the surge tank above in mine. For now I just did a drop in upgrade on the S6 tank. AEM 300lph from 034 as well. Says its good for 700hp. Rather then swapping the complicated RS6 fuel system over Im just gonna think of it like a Stage 3 upgrade in a B5 S4. Just pop a larger pump in and watch the pressure on on the rail when tuning....

PS I had to change my stock S6 pump anyway due to failure

[Corbett]

DO NOT RUN AN A1000. I can tell you from first hand experience that it is loud as hell and huge. I ran one in my rs6 when I switched to e85. Car sounded like a race car and it was so loud inside the car. Totally takes the luxury and sleeper status out of the car all together.

i ended up deleting the in line transfer pump and put 2 aem e85 pumps in the tank. One is wired up normally as the intake pump and the other is wired to the inline pump connections. Works great and super quiet. Pumps are cheap too, only about $100 a piece

[SteveKen]

I still intend to go with a stock setup to prevent any headaches. Especially with the ECU. The stock external (in-line) pump is a bosch 044 the the ECU sends 10 or 12 VDC to based on load and other conditions, but I'm more interested in having the enclosure that it is housed in because of mounting and sound deadening. The in-tank transfer pump is a high volume low pressure pump. If you research the RS6 setup, there's a suction jet pump that's uses the fuel return to siphon fuel from the driver's side to the passenger side of the tank (it's shaped like a saddle) and I've heard that the wrong in-tank pump can affect this and actually cause insufficient fuel pressure based on how the fuel returns back to the tank.