Hi everyone, I'm looking for some advice regarding the circled breather hose and valve (03C103558AA), please.

 

Does anyone know if this would contribute to a rich condition at idle if it fails, and is there an easy way to test if it’s still functioning? Could the check valve system from the timing cover to the intake (03C103474AD) have similar effects?

 

The HPFP has recently been replaced (since the photo) and has helped to an extent, but I’m still getting 15-20% negative long term fuel trim at idle. This appears to normalize under boost (the fuel trims seem to track with calculated engine load on the live data graphs). I'm not getting any logged misfires, but the idle is rough and doesn't sound healthy.

 

It's a recently rebuilt engine and measured almost 190 psi on each cylinder.

 

I'm basically trying to rule out a breather issue before moving onto the (more expensive) injectors… thanks all.

 

The Lambda correction software would adjust the fuelling to maintain the correct Stochiometric ratio within its limits of correction, a problem with the PCV system would cause a weakening of the mixture if too much air was getting in to compensate and you would see a positive fuel trim at the injectors.

 

A rich mixture could be a blocked air filter but highly unlikely unless you live in the Sahara and have done a million miles since it was changed, for me the likely culprit would be the Lambda (Oxygen) sensor but you say it does not run rich off idle.

 

MAF sensor maybe? But again if it was overfuelling due to the MAF sensor showing a higher than real airflow the Lambda correction should bring it back.

 

It sounds like you are using VCDS, have you checked the Lambda sensor output at idle and higher RPM?

Is the car running the breather the car left the factory with or has it got the 'Fix' / Modification that was fitted to try and stop the excessive oil use.

There was also a software update done with that.

 

http://briskoda.net/forums/topic/522406-help-required-please

 

 

There was a 2nd Breather Pipe mod done in Australia.  Before they got around to trying the Oil Spray Jet upgrade. 

Edited 7 September, 20241 yr by Ootohere

38 minutes ago, J.R. said:

The Lambda correction software would adjust the fuelling to maintain the correct Stochiometric ratio within its limits of correction, a problem with the PCV system would cause a weakening of the mixture if too much air was getting in to compensate and you would see a positive fuel trim at the injectors.

 

A rich mixture could be a blocked air filter but highly unlikely unless you live in the Sahara and have done a million miles since it was changed, for me the likely culprit would be the Lambda (Oxygen) sensor but you say it does not run rich off idle.

 

MAF sensor maybe? But again if it was overfuelling due to the MAF sensor showing a higher than real airflow the Lambda correction should bring it back.

 

It sounds like you are using VCDS, have you checked the Lambda sensor output at idle and higher RPM?

 

Thanks for your reply. I've been led to understand that a failed PCV system can cause either a lean or rich condition depending on whether it is stuck open or closed? I'm perhaps optimistically thinking if one of these valves is stuck closed it may be preventing the cranckcase from being vented properly, thereby causing a rich condition?

 

I'm using a Carista dongle and the Car Scanner Pro app, which can map basic OBD2 data onto a live graph. The 'tracking' of the fuel trims with engine load is particularly evident when the supercharger kicks in... at this point both long and short trims are at or around zero. I also notice the long term fuel trim occasionally rockets back up to 0 from around -20 when coming off the throttle.

 

I'll see if I can map the data for both sensors at idle and higher RPMs. I assume I'm looking for the usual yoyo-ing of the pre-cat and a steady halfway reading from the post-cat accross all ranges? Thank you/

 

39 minutes ago, Ootohere said:

Is the car running the breather the car left the factory with or has it got the 'Fix' / Modification that was fitted to try and stop the excessive oil use.

There was also a software update done with that.

 

http://briskoda.net/forums/topic/522406-help-required-please

 

There was a 2nd Breather Pipe mod done in Australia.  Before they got around to trying the Oil Spray Jet upgrade. 

 

 

Thanks for your reply also. It's a late 2011 CAVE that had the breather modification done early in its life, presumably due to oil consumption. It has the latest revision of the breather hose into the cylinder head (03C103558AA) and the check valve system from the timing case (03C103474AD). I also updated to the latest ECU software last year (9971) as it was previously running 9970 (not sure if this was the version being flashed with the breather mods at the time).

 

PS. It has had a pending ‘Rich off idle code’, and recently triggered the P0420 cat below threshold code, which has since gone away itself.

1 hour ago, boycie said:

I assume I'm looking for the usual yoyo-ing of the pre-cat and a steady halfway reading from the post-cat accross all ranges? Thank you/

 

Pre cat yes, its one of the rare times when I drag out an analogue multimeter, if the needle is swinging back and forth around the 1v( or was it 0.7v?) reference then all is well, I have yet to work on a post cat sensor, I'll have to Google to learn about them.

@boycie

OT, 

but be aware that there was a Software Update that was applied when the Upgraded Oil Spray jets were fitted. 

 

Edited 7 September, 20241 yr by Ootohere

2 hours ago, boycie said:

assume I'm looking for the usual yoyo-ing of the pre-cat and a steady halfway reading from the post-cat across all ranges?

Pre-cat oxygen sensor is wideband; so if anything, I'd expect that one to be steady mid-swing most of the time and the post-cat binary one to flick between lean and rich values.