Stumped on PCV circuit problem

[howardc64]

2000 V70 XC SE 2.4 LPT 167k miles. I'm posting here because the engine+PCV system is pretty much identical to 01s (other than how the charged air pipe flys over the engine, just about everything else in the engine is identical to the 01 V70XC and T5 I had)

1. Idle circuit pulls nice vacuum over oil filler hole using glove test
2. Boost circuit blows up glove over oil filler (foot on brake, shift in D, accelerate to 2000+ RPM briefly)
3. Also have oil residue blowing out where it can (zip tied hoses around the oil trap and see oil vapor residues forcing its way out of the trap to block hose connection)

Disassembled everything. But all the air paths appear to be clear

All paths are clear in the oil trap (nice and light as well)
- cover drain and block port, blow through head port and air comes out of the vacuum source port
- cover drain and head port, blow through block port and air comes out of the vacuum source port
- drain port is clear. cover head and vacuum source port, blow through block port and air comes out of drain port

Both air circuits in the big L shaped hose is clear
- string trimmer line from manifold connection to the vacuum source connection to oil trap
- string trimmer line from PTC connection to the vacuum source connection to oil trap

PTC is clear. Its not a valve, just straight air path enclosed in heating elements.

Drain, block, head ports on the engine are all clear. Ran string trimmer through drain port and can thread some line through and reach inside oil pan.

Dry cylinder compression test shows all cylinders around 190 PSI so shouldn't have excessive blowby due to severely worn rings.

I know of no check valves inside this particular L shaped hose (read somewhere that says later P2s have check valves in this hose). Under boost, the manifold will have boost pressure and this pressure has a direct path to oil trap's vacuum source port. The turbo circuit would have to provide enough vacuum to overcome the manifold boost and blowby to be effective. Is this understanding correct?

Anyhow, I could just replace all the PCV parts but so far can't seem to find any component that failed.

BTW, ran a vacuum/pressure gauge on the car and learn a lot about how these engines work. Tapped the CBV vacuum port and can see the manifold change from vacuum to pressure under boost. Tapped the brake booster hose at the intercooler to ETM pipe and basically have a boost gauge. Very cool to learn the theory of operations on turbo cars. Realizing manifold can change from vacuum to pressure (unlike normally aspirated car's manifold that remains always in vacuum). Everything that needs a vacuum source needs to get it from 2 places: manifold and an alternative source like just before the turbo. PCV and EVAP vacuum both work this way.

[Antherzoll]

Later models came with a check valve style banjo bolt, earlier models was just a hollow bolt.

Three reasons why the glove will blow up when the engine is loaded.
- Excessive blow by.
- Manifold pressure is pressurizing the crank case.
- Vacuum source is weak or obstructed.

Could also be when brake torquing, especially with the hollow bolt, vacuum in the intake pipe pre-turbo is not enough to overcome blowby or manifold pressure due to low air flow at low RPM. On my engine with the check valve bolt it pull in both while free revving and brake torquing.

[howardc64]

Later models came with a check valve style banjo bolt, earlier models was just a hollow bolt.

Three reasons why the glove will blow up when the engine is loaded.
- Excessive blow by.
- Manifold pressure is pressurizing the crank case.
- Vacuum source is weak or obstructed.

Could also be when brake torquing, especially with the hollow bolt, vacuum in the intake pipe pre-turbo is not enough to overcome blowby or manifold pressure due to low air flow at low RPM. On my engine with the check valve bolt it pull in both while free revving and brake torquing.

Thanks for the info on the check valve style banjo bolt. Seems like thats a better design rather than relying on the pre-turbo side to over come the manifold pressure going into the PCV system. I'll probably get the new style even though Volvo didn't call for it for this year+engine. Seems like just a better design by theory of operation.

On brake torquing on my no check valve banjo bolt system, I guess by design the pre-turbo vacuum is suppose to always overcome the pressurized manifold+blowby. Manifold pressure comes from turbo boosting and the turbo should produce the necessary vacuum to get rid of this pressure in the system. Unless of course the pre-turbo circuit is more restricted or great blowby. I'd incline to think my ~190+ PSI dry cylinder compression readings would suggest normal blowby.

I'll investigate further and post back with what I find. Thanks

[Antherzoll]

The vacuum pre-turbo would be more dependant on engine air flow than turbo pressure. Turbo pressure will increase air flow, but pressure is the restricion to flow. When brake torquing the engine it's heavily loaded, more so than normal driving. The turbo is able to generate high boost pressures at low RPM with less air flow.

In normal driving the system may operate as designed, even at WOT, as the engine will flow more air for a given rpm/boost pressure, but this is a guess. The check valve banjo bolt is a great idea and I think it should be installed on all systems, but I'm unsure if this will resolve your issue.

[howardc64]

The vacuum pre-turbo would be more dependant on engine air flow than turbo pressure. Turbo pressure will increase air flow, but pressure is the restricion to flow. When brake torquing the engine it's heavily loaded, more so than normal driving. The turbo is able to generate high boost pressures at low RPM with less air flow.

In normal driving the system may operate as designed, even at WOT, as the engine will flow more air for a given rpm/boost pressure, but this is a guess. The check valve banjo bolt is a great idea and I think it should be installed on all systems, but I'm unsure if this will resolve your issue.

Thanks for the explanation. I've been able to verify the following

- Air compressor blow nice high volume of air through the L hose from the PTC connector. Air exits at oil trap vacuum source port.
- Air compressor blow nice high volume of air through the banjo bolt port. Air exits at oil trap vacuum source port.
- Oil trap is clear on all channels
- Put a hand vacuum on the oil drain port on the block, it pulls engine oil out so its clear. Looking at the block/oil pan design, this oil drain channel opening in the pan is submerged under the oil in the pan. Thus, vacuum should pull oil out.

So as far as I can tell, the system is completely clear. So the brake torquing likely does what it did from factory... pressure in the manifold is more than the limited pre-turbo air flow can remove. But pressure in the block is probably never a good idea so best to put a check valve in the manifold vacuum supply. Just as Volvo did in their design evolution.

On my oil weeping out of oil trap's block connection. It seems without a check valve to remove the manifold pressure under boost, oil trap with get pressurized under certain conditions (high load, low RPM) Zip tie might be insufficient to keep in this pressure. I'll go with a metal clamp. But I'm guessing eliminating the manifold pressure under boost makes the whole PCV system a lot less prone to leaks+wear.

BTW, this would suggest brake torquing isn't a very good boost circuit test for for cars without banjo check valve (seems to be only on 2.5Ts)

Will report back after check valve banjo bolt installed and car back together.

[Antherzoll]

I actually have a spare one sitting around, if you were local I'd give it to you :).

[howardc64]

I actually have a spare one sitting around, if you were local I'd give it to you :).

haha, thx for the offer. I will post a summary + theory of operations explanation on my website on this "complicated" PCV system after getting it all sorted out. Actually not that complicated but certainly much more than a simple one way check valve from manifold to block in normally aspirated cars.

It seems there isn't an easy test to check the health of the boost circuit on cars without check valves other than to route a hose from the dipstick tube to the cabin to a vacuum+pressure gauge and go for a drive. Thoughts?

Have been looking at a PCV system for friend's Audi 2.0T. Audi built the whole oil trap, boost and idle circuit into a single glued together plastic valve cover that cracks at the glue seam. The oil trap function fails when cracked and dump oil into the turbo intake and pools at the lowest point in the intercooler hose until fills up, then ingests some oil into the intake and big plume of smoke out the back while the ECU goes haywire. What a mess!

[Antherzoll]

haha, thx for the offer. I will post a summary + theory of operations explanation on my website on this "complicated" PCV system after getting it all sorted out. Actually not that complicated but certainly much more than a simple one way check valve from manifold to block in normally aspirated cars.


Well if it helps any, this is an explanation I came up with a while ago. I was responding to a post where someone had asked where to tap the hoses for an oil catch can.


LOL, that's what I call it, but I'm sure there is a more technical term for it. You tapped into the hose off the intake pipe, correct?

I'll post this pic for an explanation from an earlier post in this thread.
http://tapatalk.imageshack.com/v2/14/12/30/1aa678b02ae868e7a18963a562cc538d.jpg

Starting from the top you have two fittings, one hose that goes to the intake pipe (where you normally splice in the catch can) and one pipe screw fitting for the coolant port on the block. After the large 90* in the pipe where the second set of hoses are is the connection to the stock breather box. Continuing down there is another pipe screw connection, this connects to the intake manifold with a check valve style pipe screw (rattle valve). The hose at the end attaches to the thermostat housing.

So the breather box get its vacuum from the strongest source. When idling or at cruise (not in boost), vacuum in the intake manifold will be greater than what is in the intake pipe, the system will draw its vacuum from the intake manifold (lower pipe screw fitting) causing the vapors to travel to the intake manifold. Under hard acceleration or in boost, vacuum in the intake pipe will be greater than the manifold, the system will draw vacuum from the intake pipe just before the turbo causing the vapors to be drawn into the intake pipe. The rattle valve will close as there is a vacuum being drawn in it so you won't loose boost through the intake manifold fitting or risk pressurizing the crankcase.

[howardc64]

Well if it helps any, this is an explanation I came up with a while ago. I was responding to a post where someone had asked where to tap the hoses for an oil catch can.

Looks good :) BTW, a friend I tapped the CBV vacuum port on the intake manifold and drove around, its quite amazing how often the manifold transitions from vacuum to pressure even under modest acceleration.

[Antherzoll]

Looks good :) BTW, a friend I tapped the CBV vacuum port on the intake manifold and drove around, its quite amazing how often the manifold transitions from vacuum to pressure even under modest acceleration.

Yes it is amazing, really gives you an understanding of how the turbo works, and is great for on the fly diagnostics.

Which gauge is installed. I went with the IPD gauge as it has the least amount of restriction so you can see very subtle changes in manifold pressure from intake pulses at load, it reacts very fast, instantly to 0psi from 18-19in/hg at idle when reving. At high load the needle will shake quite a bit due to it's high sensitivity, but boost pressure is still readable. Other gauges I've used with restrictors seem very lethargic.

[howardc64]

Yes it is amazing, really gives you an understanding of how the turbo works, and is great for on the fly diagnostics.

Which gauge is installed. I went with the IPD gauge as it has the least amount of restriction so you can see very subtle changes in manifold pressure from intake pulses at load, it reacts very fast, instantly to 0psi from 18-19in/hg at idle when reving. At high load the needle will shake quite a bit due to it's high sensitivity, but boost pressure is still readable. Other gauges I've used with restrictors seem very lethargic.

We just used a cheap gauge from CarQuest. I'm more of a factory computer diag tool guy but the friend is a old school car guy that suggested we hook up a vacuum gauge. I went along with it and learned a whole bunch :) What I realize now is that its a great idea to tap vacuum+pressure gauge on a manifold port check basic health of this engine (vacuum level + boost level)

[howardc64]

Well, glove over oil filler still inflates under brake torquing (just above 2k RPM), PCV trap to block elbow hose still have a tiny leak on the bottom (I tightened it with an oetiker clamp this time)

- PTC nipple is clear, air channel between PTC nipple and oil trap clear
- installed the manifold banjo bolt with check valve
- oil trap is clear
- head, block, oil drain port of the PCV system all clear
- vacuum over oil drain port syphons out oil, I'm assuming this is clear indicator of clear channel of the PCV oil drain channel to the bottom of the pan.
- dry compression all about 195psi on all cylinders
- routed silicon hose from oil dipstick hole to vacuum/pressure gauge and drove it around including boosting. Gauge scale is not very sensitive and basically never moved from atmospheric in idle or under boost. While not sensitive enough to measure precise vacuum or pressure, certainly no significant pressure showed up under load/boost.

What else could this possibly be?

On a separate note, engine runs a lot cooler now compared to before, only difference is dis/reassemble the PCV system after determining everything is clear and installing check valve banjo bolt. Quite a mystery!

[Antherzoll]

Is the intake pipe drawing enough vacuum? If you can connect the boost gauge to the blue hose off of the TCV you could see if the intake pipe has vacuum on load. I'm not sure what number to look for, but I'd say you should notice some negative pull on the boost gauge.

Stumped is right...

Is the stock air filter and air pipe installed?

Wouldn't a leak down test be a more accurate way of diagnosing excessive blow-by?

http://sbftech.com/index.php?topic=19286.0;wap2


Air escaping out the tailpipe indicates a leaky exhaust valve.Air escaping into the intake manifold tells you there's a leaky intake valve.Air escaping into the radiator indicates a compression leak into the cooling system through a bad head gasket or a crack in the head or cylinder.Air escaping into the crankcase indicates blow-by due to worn rings, a worn or damaged cylinder, or a cracked or burned piston (for further diagnosis, a "wet" leakage test is needed).

[Iroll_]

Just an idea...Could clogged intercooler input and or output hose(s) contribute to the on going issue?

[howardc64]

Just an idea...Could clogged intercooler input and or output hose(s) contribute to the on going issue?

I think the boost is fine (which would suggest intercooler is fine), I can see 0-5 PSI boost pressure in the manifold depending on acceleration level.


Is the intake pipe drawing enough vacuum? If you can connect the boost gauge to the blue hose off of the TCV you could see if the intake pipe has vacuum on load. I'm not sure what number to look for, but I'd say you should notice some negative pull on the boost gauge.


Yeah, I think checking out vacuum level before turbo would be a good next step.



Is the stock air filter and air pipe installed?


Yes, totally stock, this is a 2000 2.4T. Engine components looks identical to early P2s in nearly every area including PCV system. PTC has 2 connections: heater electrical and vacuum source to the trap.



Wouldn't a leak down test be a more accurate way of diagnosing excessive blow-by?

http://sbftech.com/index.php?topic=19286.0;wap2

Good point, I'll do that next. Hope I don't have a crack cylinder walls that I read about on these 5 cylinder engines.

I do have another ominous symptom that might be related. Engine has a flutter sound (like "slightly" missing in 1 cylinder, not a complete miss like unplugging a coil) when cold at around 2500 RPM under load. I have boost and descent acceleration but can hear this flutter sound. Once the engine warms up, this sound is a lot less prominent. I have an extra coil and rotate it through all 5 cylinders so I'm certain its not the coil. All plugs are new as well (symptom both before and after plug change). Checked the turbo CBV and its good, fixed a blown EVAP circuit check valve, and cleaned the injector pump on the brake booster vacuum circuit (the narrower channel allowed more air to flow after cleaning). Nothing I did so far has changed this flutter sound under load when cold.

This might suggest something is getting sealed after warming up.

[Iroll_]

A lazy or slow vvt solenoid?
Before everyone thinks I am crazy...It's my understanding that vvt solenoid and oil system( exhaust and or intake ) has the potential have a large effect on vacume.

http://www.brakeandfrontend.com/phaser-style-variable-valve-timing-system-controls-and-operation/

[The Landshark]

From your description it sounds like an egr valve stuck or clogged, but i don't know that engine or whether you have to have egr on cars over there(egr = exhaust gas recirculator)

[Antherzoll]

Since you have a boost/vacuum gauge, what does the engine read in park once fully warm?

Boost seems a bit low but the gauge could be off. Max psi should be around 6-8psi depending on ambient conditions. Bosch ME is a torque demand system, it will only make enough boost to meet the torque target so 5psi could be possibly meet max target, but it'd be nice to see what the ECU is demanding.

[howardc64]

From your description it sounds like an egr valve stuck or clogged, but i don't know that engine or whether you have to have egr on cars over there(egr = exhaust gas recirculator)

Thanks for the idea. However, no EGR on this engine.

[howardc64]

Since you have a boost/vacuum gauge, what does the engine read in park once fully warm?

Boost seems a bit low but the gauge could be off. Max psi should be around 6-8psi depending on ambient conditions. Bosch ME is a torque demand system, it will only make enough boost to meet the torque target so 5psi could be possibly meet max target, but it'd be nice to see what the ECU is demanding.

I'll look at the readings again and post it tonight. Just to confirm, tapping the CBV vacuum port to read manifold pressure is right place to get these readings?

[Antherzoll]

I'll look at the readings again and post it tonight. Just to confirm, tapping the CBV vacuum port to read manifold pressure is right place to get these readings?

Yes sir!

Also what's your elevation? I get 18-19in/hg here in Toronto, but when i was in Wyoming I was getting 13-14in/hg, gave me a huge scare until I remembered elevation. Sea level should be 18-20in/hg. Above 2,000 feet vacuum reading will be about an inch lower per each 1,000 feet rise in elevation. Make sure all accessories are off.

[howardc64]

Also what's your elevation? I get 18-19in/hg here in Toronto, but when i was in Wyoming I was getting 13-14in/hg, gave me a huge scare until I remembered elevation. Sea level should be 18-20in/hg. Above 2,000 feet vacuum reading will be about an inch lower per each 1,000 feet rise in elevation. Make sure all accessories are off.

Ok, got some data to look over

- 500 feet above sea level reading about 18-19in/Hg at idle with warm engine.
- Made myself a handy dandy manometer : silicon tubing in dipstick hole routed to cabin with latex glove attached tightly with rubber band sitting on the dash. Vacuum in idle and blows up when boosting.
- Friend who was navigator said he saw 6+ PSI boost in previous test drive when we were driving around previously (tapped intercooler pipe at brake injector connection)

Also took VIDA graph attached below boosting going up a hill. Black lines are RPM (caption not visible), looks like everything is expected. Boost pressure climbs up to 1330 hPa (19.3 PSI or about 5+ PSI boost) as RPM goes to 2700+. Didn't floor the accelerator but demanded quite a bit of power. Engine Torque control flatlines at 511 Nm, not sure if it suppose to be like that. Calculated torque is going to about 250 Nm under boost.

So its pretty clear the blowby is higher than vacuum source at boost. So onto a leak down test and/or reinspecting the PCV boost circuit for the 3rd time. Here is my PCV test/inspection procedure just to confirm

- idle circuit vacuum test shows good suction on both dip stick and oil filler hole.
- compressed air applied at the PTC hose connection on the big L pipe inflates glove attached oil filler hole. And inflates glove attached to dip stick hole with oil filler cap on. Vacuum applied to PTC hose connection on the big L pipe will shrink a glove connected to the dip stick hole. So clear channel between PTC and block and head is clear.
- compressed air blown into the port on the block blows air out of the oil filler hole.
- compressed air blown into the oil drain port makes oil bubble sounds and blows air out of the oil filler hole.
- PTC nipple looks nice and clear. Shine a flash light through it and light shows up in the fresh air pipe. Just shiny metal sides internally where the heaters are
- oil trap is light. All ports unblocked (didn't have to clean it) When blocking 1 of the 4 ports, remainder 3 ports flows air (eg block head port, blow air from block port, exits vacuum+drain port. block block port, blow air from head port and exits vacuum+drain port). Run some stiff wire through every port, goes all the way through, no blockage.
- Engine block port and drain port is nice and clear (didn't have to clean it)

Hooked up a coarse hose+vacuum gauge to PTC nipple and brake torque (L hose PTC connection vent to atmosphere), too little vacuum to register. Wrapped a latex glove around the hose and I can see vacuum under brake torque, the rate the PTC nipple glove shrinks seems slightly (this is subjective of course as I have no high precision vacuum+pressure gauge) less than the rate dipstick hole glove inflates.

7378

[howardc64]

Came across several posts (including one by our friendly Volvo tech cattlecar) that says small positive pressure under boost is completely normal.

http://forums.swedespeed.com/showthread.php?207020-Another-PCV-Question-positive-pressure-at-boost

So I decided to revisit theory of operations

1. The only high vacuum source in the car is the intake manifold when not pressurized under boost. Pistons and throttle plate work together to create this high vacuum source.
2. Fresh air pipe in front of turbo has no restriction like a throttle plate. Engine+turbo just pulls as much air as it wants. Certainly air flow towards the turbo but since there is ample air supply, it will only produce a slight decrease in pressure so the vacuum level from this source will be relatively small. I measured it at PTC nipple under boost, it doesn't register at all on my coarse vacuum gauge. Attached a latex glove and it reveals a slight vacuum. Much less than intake manifold at idle.

So it seems the PCV boost circuit should really be thought of as mostly a vent. The question then is weather the vent size is sufficient to vent the blowby volume.

Since the boost circuit is mostly a vent, then crankcase pressure measurement should show slightly positive under boost IF the vent is clear. If the vent is clogged, pressure will be much greater.

I think cattlecar's explanation on the above link on normally aspirated cars clarified this for me. Intake manifold on NA cars is also not a perfect source of high vacuum all the time either. It depends on the throttle demand.

Anyway, like to hear other knowledgeable experts understanding of how this system works.

BTW, I also found this article below that gave a great explanation on blowby rate to calculate sizing the PCV. In summary, it says

- blowby is higher at low RPM
- piston ring is the main blowby source. On turbo charged cars, valve guides and seals is another blowby source (manifold has boost PSI pressure, if valve guides and seals leak, this pressure will get into the head)

http://www.106rallye.co.uk/members/dynofiend/breathersystems.pdf

I'm guessing why some people have slight vacuum under boost while others have a slight pressure while PCV system is completely clear probably depends on the minute amount of vacuum we are starting with on the original design. If blowby were to increase on an older engine for example, it may go above the original design vacuum spec. On older Volvos, I read people install 5/8" diameter hose (factory = 3/16") to the PTC to increase vacuum/vent to aid the higher blowby of older engines. I wonder if Volvo also increased the diameter of the boost circuit hose on the newer P2s? Volvo kept on changing and I guess improving? this PCV design like every couple of years since the mid 90s.

[Scopeman]

I have thought that the large volume of air flowing past the PTC nipple causes a pressure drop at the PTC, helping to evacuate the large breather pipe and plumbing, and sucking blowby out. Certainly this system has limited capacity, and a seemingly marginal design.

[howardc64]

An update for those curious about this PCV system.

First, the best way to see the crankcase pressure is to route a hose from oil dip stick hole to the dash (make sure hose isn't crimped, probably need to lift up some engine compartment seals and leave the hood unlatched). Rubber band a latex glove on the end of the hose and go for a drive. You can see the the crankcase pressure under all kinds of conditions : idle, light load, heavy load, cruise etc...

Now onto my PCV

Initial Condition : All hoses, oil trap, vent pathway and oil drain channel inside the engine are all clear. I blew air through all of them to confirm.

Step 1 : Switched the banjo bolt with an updated design with a check valve. This prevents the positive pressure from entering the intake manifold under boost from entering the PCV circuit.

Test drove it with the diag setup mentioned above. Glove inflates under heavy boost.

Step 2 : Upgraded PCV's boost circuit by using a 5/8" ID hose (found this trick from pre-P2 owners, I had to tap it and route a small hose to the banjo nipple for the idle circuit vacuum). This worked great, still some glove inflation under heavy boost but a lot less. FYI, The OEM boost circuit piping looks to be about 1/4" ID aluminum pipe so 5/8" ID is a big upgrade air flow volume.

Now my glove still inflates slightly under various conditions. Heavy load uphill is most repeatable but have seen it also just cruising at 2k+ RPM briefly.

Anyhow, if anyone is curious how the PCV system actually behaves under various conditions, just do the above setup and watch it while driving around.

[Antherzoll]

Interesting, I'm going to try this.

[guymon]

Officer, don't mind the latex glove rubber-banded to a tube, next to me...

I think a photo is needed, Howard. ;-)