P0171 fuel pressure sensor?

[raoul5r]

Hi everyone,

I have been chasing the source of my P0171 code for quite some time now. So far I had replaced the PCV Valve, front 02 sensor, N80 Purge valve, camshaft follower, camshaft sensor and seals. The car had been smoke tested and no leaks appeared.The car drives normally and I don't really feel anything abnormal when driving. The only thing I do notice is a bit of lag when accelerating at times which I am assuming is the fuel pressure sensor but I am not too sure if it is. I attached 2 freeze frames and was wondering if anyone can shed some light in this situation.

Thanks !

Freeze frame report generated by Torque for Android
================================================== =======

Vehicle VIN: WAU
Vehicle Manufacturer: Audi
Vehicle Calibration ID: 8E1

Freeze frame information:
------------------
Fuel Status = 0 byte
Engine Load = 23.922 %
Engine Coolant Temperature = 71 °C
Fuel Trim Bank 1 Short Term = 8.594 %
Fuel Trim Bank 1 Long Term = 21.875 %
Engine RPM = 2,041.5 rpm
Speed (OBD) = 59 km/h
Timing Advance = 12 °
Intake Air Temperature = 5 °C
Mass Air Flow Rate = 15.3 g/s
Throttle Position(Manifold) = 19.216 %
Run time since engine start = 903 s
Fuel Rail Pressure = 1,145.798 psi
Barometric pressure (from vehicle) = 14.359 psi
Voltage (Control Module) = 14.206 V
Engine Load(Absolute) = 37.255 %
Commanded Equivalence Ratio(lambda) = 1
Relative Throttle Position = 8.627 %
Ambient air temp = 4 °C
Absolute Throttle Position B = 18.824 %
Accelerator PedalPosition D = 29.02 %
Accelerator PedalPosition E = 29.02 %

End of report.




Freeze frame report generated by Torque for Android
================================================== =======

Vehicle VIN: WAU
Vehicle Manufacturer: Audi
Vehicle Calibration ID: 8E1

Freeze frame information:
------------------
Fuel Status = 0 byte
Engine Load = 20 %
Engine Coolant Temperature = 70 °C
Fuel Trim Bank 1 Short Term = 4.688 %
Fuel Trim Bank 1 Long Term = 20.312 %
Engine RPM = 2,213 rpm
Speed (OBD) = 64 km/h
Timing Advance = 17 °
Intake Air Temperature = 2 °C
Mass Air Flow Rate = 16.22 g/s
Throttle Position(Manifold) = 17.647 %
Run time since engine start = 579 s
Fuel Rail Pressure = 1,196.561 psi
Barometric pressure (from vehicle) = 14.504 psi
Voltage (Control Module) = 14.135 V
Engine Load(Absolute) = 30.98 %
Commanded Equivalence Ratio(lambda) = 1
Relative Throttle Position = 7.059 %
Ambient air temp = 2 °C
Absolute Throttle Position B = 17.647 %
Accelerator PedalPosition D = 28.235 %
Accelerator PedalPosition E = 27.843 %

End of report.

[supple]

I feel like this is like the third thread about a fueling issue in the last couple weeks. It looks like you've replaced a bunch of stuff already. I would take a look at replacing the fuel filter since its cheap then replacing the in-tank fuel pump.
P0171 is a fuel trim code, if you can log the pump load % it should be 50% at warmed-up idle.

[80sGuy]

I got that code last year when I found out that my air box wasn't closed tightly. I replaced the air filter and also cleaned out the little snow screen filter inside the snorkel tube, closed it really tight and the code went away. Immediately felt better throttle response. It could the simplest things. So check for air leaks starting with the box.

[raoul5r]

Update : After replacing the n80 valve (replaced it at the time of posting initially) the car felt alot more free, took it for a pull and flew back in my seat which i had not experienced before. The car drove a amazing but after a day of driving i experienced that lag and hesitation again which resulting in the check engine light. I hooked up my torque pro app and saw that after clearing the light the car idled around 2.8 to 3.x g/s during cold start warm up and the engine idled very quiet. After driving around for a bit those numbers changed to 2.5 and below (lowest recorded was 1.0, by the time the CEL came back on). After reading some posts and seeing that that other stock cars were hitting 170-180 g/s at 6500 rpm i decided to test mine, I only got 121 g/s. I'm only left to believe that it may an issue with the MAF, which I had cleaned out before but the light came on after still.

And yeah I checked out the air box and everything appeared to be secure and I had changed the filter not too long ago so its brand new. I had ordered a new fuel rail pressure sensor and have yet to put it in. Also I had looked into on how to log the pump load % in torque but could not figure out how.

Any ideas guys ??

[Van Black]

I don't think you can see the pump load in Torque. I also use it and it doesn't appear as one of the supported sensors you can log. You can check that in the settings menu

[kcoddah77]

So what happened?

[EvolutionArmory]

Update : After replacing the n80 valve (replaced it at the time of posting initially) the car felt alot more free, took it for a pull and flew back in my seat which i had not experienced before. The car drove a amazing but after a day of driving i experienced that lag and hesitation again which resulting in the check engine light. I hooked up my torque pro app and saw that after clearing the light the car idled around 2.8 to 3.x g/s during cold start warm up and the engine idled very quiet. After driving around for a bit those numbers changed to 2.5 and below (lowest recorded was 1.0, by the time the CEL came back on). After reading some posts and seeing that that other stock cars were hitting 170-180 g/s at 6500 rpm i decided to test mine, I only got 121 g/s. I'm only left to believe that it may an issue with the MAF, which I had cleaned out before but the light came on after still.

And yeah I checked out the air box and everything appeared to be secure and I had changed the filter not too long ago so its brand new. I had ordered a new fuel rail pressure sensor and have yet to put it in. Also I had looked into on how to log the pump load % in torque but could not figure out how.

Any ideas guys ??

Your MAF should read about 2.5gs at warmed up idle. If your reading dropped down to 1gs and your code came back and your peak MAF is considerably lower than normal, it's pretty safe to say you might need a new MAF or your wiring to it is faulty.