Horner

Ill start by saying im running out of ideas on how to fix my reoccuring p0171 bank 1 system lean code. I have cleaned the maf and got better a couple months ago but the code came back. i cleaned it again and it threw the code almost immediately. i have done a boost leak test and have repaired a couple rubber hoses that were leaking. I tested it once again and it holds boost but im still getting the p0171. Im not really sure where to go next. the maf reads and changes when the rpm changes while looking at the limited live data on a cheap *** scanner. If anyone has any ideas please let me know. btw its a 2001 a4 1.8t 5spd quattro w/ awm

Prospeeder

its the maf. cleaning it wont do anything. Replace it. I see it pretty commonly for lean codes only if there are no vacuum or air leaks present.

Horner

Update: ive replaced the maf and now im getting a p0172 system too rich code. Even at idle the LTFT is -23% i dont understand how you can go from one extreme to another. I will say it acts like it has a hiccup about 3k rpm in 1st gear at full boost, but it runs like a scalded dog. It wont hiccup in any other gears but 1st.

Horner

BTW using search feature as we speak.......

Prospeeder

Look up something called a suction jet valve. Its got 3 ports on it. And There are service bulletins about it causing mixture codes. Especially rich codes. Check cam timing, leaky injectors, bad o2 sensor, clogged exhaust, uneven compression, or even the Evap purge solenoid stuck open cause rich codes. Sounds to me like you had 2 issues. MAF was bad which almost always cause lean codes. Now that its not lean, you have another issue causing a rich condition.

Prospeeder

Fuel Mixture codes

One of the Diagnostic Trouble Codes (DTCs) shown above is stored in the Engine Control Module. These codes may be accompanied by an Malfunction Indicator Light (MIL) -K83- illumination.

This condition may be also due to a clogged Suction Jet Pump.

Production Solution

N/A

Service

In addition to other diagnosis for these DTCs (Refer to Repair Manual for a Rich Fuel Trim or Guided Fault Finding) also check if suction jet pump is clogged as follows:




- Remove 2 hoses from suction jet pump -black arrows-.
- Blow air through side port -white arrow-.
- If air exhausts through lower port:
TIP:

Suction jet pump is not clogged. Continue with diagnosis.

- If air does not exhaust through lower port:
TIP:

Suction jet pump is clogged. Replace suction jet pump.

Horner

UPDATE- I got my suction jet pump cleaned out and working while my new one is on order. While i was at it i replaced the plugs, fuel filter, thermostat(failed open), and the upstream 02 sensor. While i was replacing the thermostat i cleaned the TB and the IAT all at one time. Got everything back together and drove it and my fuel trims are still pulling alot of fuel as if the car is running rich. I dont have a test port on the fuel rail to check pressure so im at a loss? The car feels like it has a very slight misfire but when i pull the misfire data it shows no misfire or maybe like 1 or 2 at upper rpms with NO CODE. I am ordering new coils to be safe but it still doesnt explain the rich code p0172. The car pulls hard but still lays over hard around 3-4k rpms. I know the turbo is running out at that time but i was still expecting it not to fall on its face.

BTW: BIG THANKS to Prospeeder for the insight to the suction jet pump. Cheers!

Prospeeder

Had a 1.8T A4 that constantly had rich codes. Cam timing was a tooth off. Also had another one, one cylinder had low compression. That cylinder isnt going to use as much fuel as the other three, and will trick the o2 sensor and pull fuel, this leans the other cylinders, and then see that and causes it to richen the mixture. Viscous cycle that ends up making LTFT add fuel.