2006 Octavia Vrs Running Lean

[PyroboyUK]

Hello,

My 2006 Octavia 2.0tfsi has unfortunatly presented me with an Engine Warning Light over the last few weeks that im struggling to get to the bottom of.

When the light first appeared I took it straight to my local VAG specialist. They put it through the diagnostics and asked me what kind of fuel I was using in my car, with my daily travels I normally fill up with standard Shell Unleaded. Once brought up I was told that this type of engine could not run on standard unleaded and this was triggering a "Fuel Mixture" issue. I was a little dissapointed at this diagnosis as after doing research when I bought this car I was under the impression that increasing the RON would only increase performance and after 2 years of running on standard unleaded this engine light never appeared.

So I thought I would go down the Super Unleaded fuel route and I put a couple of tanks worth in the Octavia, unfortnatly the engine light came back on so quick I never had the chance to give it a proper run with Super as the residual fuel would still be in the system.

Luckly a friend has a scanner and was able to reset my engine light and even with Super Unleaded the light was appearing!

So using this scanner I did some digging into what the actual fault code was that was causing this Engine Light to appear. The DTC is P0171 & P0171P.

It appears from all of the OBD websites including Ross Tech that this means Bank 1 system is Too Lean. My first port of call was to clean the MAF sensor as it was a 5 minute job however this did not work. After doing a little more digging it seems this could be caused by a faulty PCV.

So I went to check if the PCV valve had failed (According to a few sites this is a common component to fail), and when I took the component off it seems that the Non Return valve leading to the Intake Manifold had failed open (See Photo Below):

The photo will hopefully show the non return valve slipped out of place.

The photo below shows the N revision valve which is completly redesigned from the original in my octavia:

I was quite concerned when I observed the amount of oil in the connecting pipe between the PCV and Intake Manifold! This may explain my Octavias level of oil consumption, its not massive but seing that oil in the pipe doesnt make me feel great.

So this was a quick and cheap fix that when fitted I noticed an instant change neautralising a rough idle that I had noticed, the revs stayed level it was just vibrations and knocking felt in the cabin. My hopes where really up after this fix as logic would suggest that if this valve had failed open then this would allow gas from the crankcase to enter the intake manifold when the car is under idle.

I should point out at this stage after 5 resets of the light i can confirm this engine light ONLY occurs when the car is under idle. Hundres of motorway miles with the turbo spooling does not set it off but as soon as I idle it comes on!

My thoughts are that if the vehicle is on Turbo Boost then pressurised air entering the intake manifold will be allowed straight through the failed PCV and into the crankcase!

So after the PCV fix a journey to work in the morning put the light straight back on, it came back on when reversing the car into a space at low revs.

This is quite a few events to put down and hopefully it makes sense reading all this, does anyone know of the Engine Lean fault and any other components that could have failed? All I can think at this stage is that some sort of air intake pipe leading to the engine has a hole allowing air to enter from atmosphere.

I should also point out that no drop in performance can be felt and my MPG is still up at about 38mpg so I cant say the car is running poor, just an engine light that keeps appearing! I was also going to remove a sparkplug as if the car is really running lean then the plugs "should" be white.

[martziniuk]

Is it remapped?

[PyroboyUK]

No, the car is completely standard.

[stever750]

Faulty maf?

[Bogwoppit]

How many miles has it done and have you checked the fuel pump follower for wear?

see here for how to check/change:

http://www.briskoda.net/forums/topic/142836-how-to-change-fuel-pump-cam-follower-on-2-0-tfsi/page__hl__+follower#entry2108762

and

http://www.briskoda.net/forums/topic/170522-cam-follower-wear-at-28k-miles/page__hl__+follower#entry2090142

Edited 3 July, 2012 by Bogwoppit

[martziniuk]

Ahh if it were Revo then I may have had an answer. Check the lower pipes where it goes into the intercooler for leakage, tell tale signs are oil around the couplings.