P0171 Lean code Pirelli edition

[patsully]

Hey guys.

2009 MK5 pirelli edition with unitronic stage 2+ tune.

Currently getting P0171 but not CEL. When I clear the code the car has full power but after roughly a day of driving it seems to have reduced power.

Have checked block 32 on VCDS and it's
-4.7% for short term and +24.7 for long term.

Have cleaned MAF
New coils and plugs
New fuel filter

Does this suggest a vaccum leak?

Cheers guys.

 

[BurgerGuy]

It could be. Bad/poor fuel can cause trims to ride one way or the other too.

I believe +20 is the threshold for a lean condition on the LTFT. If you have a boost gauge, where does it sit at idle once the engine is warmed up and the AC / heat is off? The vacuum line that feeds the brake booster is known to crack over time and there's another line in that general area that can also crack. I think it's right between the HPFP and intake. The hose was cracked where it connects. You couldn't tell until it was broken until removing it. I also ended up replacing these things as they had issues so might be worth checking on your car:

• The valve cover. Oil fill port/neck was venting as well as other areas such as the internal PCV channel (front PCV to rear breather) and where coils go in.
• Front PCV because previous owner installed a block off plate. I got the most updated version for the type my car uses. Long story short, some of the FSIs are setup with a valve on the rear breather tube and others have that valve incorporated into the front PCV and are paired with a rear breather hose that has no valve in it.
• Rear PCV breather tube. Was seeping where it connects to the valve cover on the back of the engine.

Every car is different as the higher trims could be the result of the engine's age alone, but don't forget that cooler weather will drive the LTFT higher since air is more dense which means lean! I typically don't go higher than +17 - +19 on the LTFT in the winter.

 

[patsully]

Hey Mate thanks for the reply. I've had the brake booster lines replaced as they were cracked but still same issue. I'll check the other suggested places and see if they may be the culprit. I've used BP 98 and been through a few tanks of it and still getting the fuel trim issue.

I reset the fuel trims today and the partial fuel trim creeper up after about 10 mins of driving to about +24% I think it's 25% when the CEL comes on. Could it also be a MAF issue? Also are their any other things I can check on VCDS that may help?

Appreciate your help. Cheers

 

[patsully]

Solved:

Turns out it was the cheap intake I was using. It was an unbranded one designed for the MKV but the location of the Maf and diameter of the piping was throwing the trims out. Have now replaced with a CTS intake and my fuel trims are around 3% and the car goes much better.

 

[BurgerGuy]

Nice! That'll do it.