Fuel pressure woes

A6 All/ S6 All
#1

Hey guys, looking for some guidance here. So I’m driving my D3 S8 (V10) yesterday when I’m idling at a stop light and the car just quietly stalls. I barely notice. Start it back up, it hesitates a bit when driving but can make it to the next stop light, then dies again. This happens a couple times. If I turn it on and let it idle, it will idle for about 30 seconds then just stall. I’m very close to home so I try starting again and driving, but EPC light goes on and limp mode. I clear the codes, wait 15 min, start it up again, and same thing happens. Then I clear the codes, wait 15 min, start it up, and drive 10 minutes home without any issues. When it starts, maaaybe it’s cranking a slight bit longer than normal…otherwise no preceding symptoms. Battery is full. Gas tank is full. Otherwise the car is (engine-wise) stock and pretty new to me and I have not done coil packs/plugs/fuel filter recently.

Here are the codes I’m throwing:

008756 - Oxygen (Lambda) Sensor B2 S1
P2234 - 004 - Signal Shorted to Heater Circuit - Intermittent
012555 - Low Pressure Fuel regulation
P310B - 008 - Fuel Pressure Outside Specification - Intermittent
000139 - Low Pressure Fuel System
P008B - 001 - Pressure too High - Intermittent
000135 - Fuel Rail/System Pressure
P0087 - 002 - Too Low - Intermittent
006435 – Please Check DTC Memory of ECU Number
P1923 – 008

So I’m thinking maybe dirty/clogged fuel filter? Maybe mechanical failure of HPFP? G410 fuel pressure sensor? It’s currently my DD because the 5cyl turbo is under the knife, so I’d like some ideas to try here. I do have VAGCOM so can log fuel pressures or whatever if someone can give me some guidance. Thanks in advance!!

#2

Chances are its not a clogged filter. It can be that but the S8 has two in tank low pressure pumps and it seems like its not uncommon for one of them to poop out. I would look at the low pressure pump. Log the actual and requested values at idle. That will tell you much more. Its not a hard fix

Where are you located

#3

Grab a log and share the values. You should be able to tell tho. You should see a big gap between actual and requested. You can also look at the pressure at the rail pump but that is kinda the same thing.

Also look into ECU 2 and see what codes that gives you back

#4

Thanks for the replies. That’s consistent with what I learned researching today. My thoughts are that the right sided lpfp is going bad because it seemed to stall after about 30 seconds (I didn’t time it because I knew nothing about the primary and secondary lpfp system). Miraculously though, the car started and ran just fine today…I’m for sure going to change the fuel filter but am also leaning towards replacing the right sided lpfp, and maybe even the left while I’m in there. Thoughts?

#5

I would still log the car and get an idea on what blocks you need to log for the LPFP and the pressures. This is a good reason to log it now if the car is running ok Vs when you have issues. Sounds like something just went weird with the pump for a few hours.