Understanding the MK7 PCV function, retrofitting the MK8 PCV, and why catch cans are bullshit(IMO)

[Klrider44]

My tuned 19 GTI doesn't smoke on BL PCv and a cc.

What cc are you using, BMS?

 

[GTIfan99]

Just had my shortest track day.

Laps 1-3 warming up tires. Laps 4+5 drove 7/10ths and got smoke after a brake -> right + throttle turn (T1 at NJMP Lightning). Car went into limp mode + went home, will go through logs and share in a bit.

Back to the plate pcv, strike 1 for the car.

Edit: oil was exactly halfway on dipstick cold

Mk8 pcv?

 

[GTIfan99]

What cc are you using, BMS?

Yes.

 

[Klrider44]

Yes.

I wonder if there is actually something to the length of the hoses. BMS does emphasize that and I have seen Vargas mention it as well. They both have the can up near the firewall.

 

[yakev724]

Mk8 pcv?

Yes

 

[scrllock]

I wonder if there is actually something to the length of the hoses. BMS does emphasize that and I have seen Vargas mention it as well. They both have the can up near the firewall.

100%. i'm sure it's not just for convenience sake that VW put the TCR AOS up in the corner closest to the PCV/inlet, compared to where most kits besides BMS reside.

 

[Klrider44]

100%. i'm sure it's not just for convenience sake that VW put the TCR AOS up in the corner closest to the PCV/inlet, compared to where most kits besides BMS reside.

If the MK8 PCV doesn’t work for me I might give the BMS catch can a try with different combinations.

 

[yakev724]

Welp, here's a log snippet of 1 lap earlier today. Getting quite a bit of knock throughout the lap, especially on the straights. Car is tuned for 31psi but given the cooler temps now I'm seeing up to 34psi. Wish I had past logs to compare with but I'll be back to the track in 2 weeks to do some A/B testing hopefully. On top of the smoke clouds I was down about a quart of oil after 3 warm-up laps, 4 moderately fast laps (after which it went into limp mode), and the 300 mile round trip home.

One finding is the amount of knock isn't necessarily correlated with smoke - on the start of the 2nd lap below I was slower due to traffic, knock was only -1 degree for an instant but smoke cloud was as significant as it was on other laps.

Instead of going straight back to my spulen (plate) cc maybe I'll try the BMS can in line with the mk8 pcv first.

 

[DerHase]

I decided to go ahead and try this out on my 2017, since I was seeing a bit of oil weeping around my oil filler cap and would sometimes smell (but not see) burning oil after hard driving (autocross, hard pulls on expressway). I even went so far as to use the Liqui-Moly UV dyed oil to try to find a leak. I never saw smoke out the rear after turning under load. Local shop had suggested either PCV problem but didn't seem too worried about it. But the smell would bother me, and I love to tinker, so here we are.

The car is modified, but is low miles. I'm only at 33k miles, because I live in the city and take public transit most of the time, most of the miles are highway. It's tuned with GIAC stage 2 ECU & TCU. I'm using the IE Turbo Inlet pipe, so of course the little press fit bung they use came out and made it a nightmare to put the Tiguan PCV breather hose on. After about 40 minutes of fiddling with it with various hooks and small screwdrivers I was able to get it off. I think the OE mk7 hose is probably usable afterwards, but I might just go with the ECS AN hose if it's not (a problem for future me to figure out) if I have to go back to the MK7 PCV assembly.

So far, no smells. So that's good. I did an oil change the same day that I did this, so I'm going to monitor oil consumption this winter. I haven't had a chance to put a lot of hard pulls on it, nor do I have the OBDII dongle to capture logs (yet), but I'll be sure to update if there's any negative impact.

Just had my shortest track day.

Laps 1-3 warming up tires. Laps 4+5 drove 7/10ths and got smoke after a brake -> right + throttle turn (T1 at NJMP Lightning). Car went into limp mode + went home, will go through logs and share in a bit.

Back to the plate pcv, strike 1 for the car.

Edit: oil was exactly halfway on dipstick cold

Both of you do me a favor and fill this out if you haven't already:
https://docs.google.com/forms/d/e/1...FxiSOUdTnRnTIfaSi-YuleZw/viewform?usp=sf_link

If anything ever changes, just submit again and I can scratch the original if problems show up over time.


This stupid fucking science experiment just gives more questions than it gave answers.


Also @yakev724 - generally knock from oil ingestion is associated with a LOT more registered knock... unless maybe whatever tune you're on has the sensors numbed to hell perhaps. Smoke out of the tailpipe is obviously no good either way though. What is your engine code?


It's looking like the early cars (15-18) are the only ones with issues so far? I wonder if the newer engines have some kind of revision in the block passages for the lower "coarse AOS"?

 

[mrmatto]

DKFA is 2019+ so that could add up

I found an old post with someone saying the PCV system was improved in 19+ but no details.

 

[yakev724]

Also @yakev724 - generally knock from oil ingestion is associated with a LOT more registered knock... unless maybe whatever tune you're on has the sensors numbed to hell perhaps. Smoke out of the tailpipe is obviously no good either way though. What is your engine code?

done, wanted to shake it down on track before filling out the form. engine is CYFB

I have a suspicion my tune has always been allowing up to 3-4 degrees, car didn't feel down on power at all. Also last time I did a compression test I was getting mid 170s across the board.

Tentative plan is to run a session with the mk8 pcv + bms cc next time out, then let the engine cool and swap to my plate pcv/cc and run the rest of the day to compare.

 

[Mosquito]

Welp, here's a log snippet of 1 lap earlier today. Getting quite a bit of knock throughout the lap, especially on the straights. Car is tuned for 31psi but given the cooler temps now I'm seeing up to 34psi. Wish I had past logs to compare with but I'll be back to the track in 2 weeks to do some A/B testing hopefully. On top of the smoke clouds I was down about a quart of oil after 3 warm-up laps, 4 moderately fast laps (after which it went into limp mode), and the 300 mile round trip home.

One finding is the amount of knock isn't necessarily correlated with smoke - on the start of the 2nd lap below I was slower due to traffic, knock was only -1 degree for an instant but smoke cloud was as significant as it was on other laps.

Instead of going straight back to my spulen (plate) cc maybe I'll try the BMS can in line with the mk8 pcv first.

View attachment 294606

View attachment 294607

So on the knock avg. -4 certainly isn't good and you certainly do have smoke as you say. In the case of DerHase, knock due to oil showed to be outrageously high, were does that differ from say an aggressive tune with knock, who knows.
In this case, what actually catches my attention is your tune for 31 psi going to 34 psi. Mine is set for 27 psi and I only hit 28 psi in the peak of summer where temps keep torque from reaching requested...? I always see lower boost peaks in winter where ideal temps come into play and never see more than 1 psi in either direction. Just my experience/car/tune. 3 psi to me is quite a bit.

In the case of the BMS CC, as much as I like that option vs other similar ones. The science doesn't back up (to me) the notion that a delay in vacuum pull from the TIP by empting the CC volume of ambient pressure is going to keep the crankcase vent port from drawing up oil past the bypass valve into the right side of the assembly where the intake check valve is prior to the intake manifold. Sadly, you might be better off installing the Spulen kit back on.

 

[yakev724]

So on the knock avg. -4 certainly isn't good and you certainly do have smoke as you say. In the case of DerHase, knock due to oil showed to be outrageously high, were does that differ from say an aggressive tune with knock, who knows.
In this case, what actually catches my attention is your tune for 31 psi going to 34 psi. Mine is set for 27 psi and I only hit 28 psi in the peak of summer where temps keep torque from reaching requested...? I always see lower boost peaks in winter where ideal temps come into play and never see more than 1 psi in either direction. Just my experience/car/tune. 3 psi to me is quite a bit.

Gotcha. Looking at logs I'm seeing cases where torque is 550Nm+ but car is requesting as much as 650. Will hit up my tuner, I don't want to be running this much boost.

 

[DerHase]

Gotcha. Looking at logs I'm seeing cases where torque is 550Nm+ but car is requesting as much as 650. Will hit up my tuner, I don't want to be running this much boost.

View attachment 294642

That's basically how everyone tunes in the aftermarket. If your PUT = PUT SP and not overshooting it by a ridiculous amount, it's fine. It's tuned to target PSI, not torque.

I request 500 or 550nm and my car has no way of even making that.

 

[yakev724]

That's basically how everyone tunes in the aftermarket. If your PUT = PUT SP and not overshooting it by a ridiculous amount, it's fine. It's tuned to target PSI, not torque.

I request 500 or 550nm and my car has no way of even making that.

Ah gotcha, that makes sense hah. Will have them dial it back a bit still. Apols for derailing thread