1.4T PCV Explained

[Scot]

Nice write up Pre!
The vapor you smell at hot start could be attributed to the EVAP system. It has a solenoid that allows fuel vapors from the gas tank to be re-ingested by the engine via the intake manifold as pressure builds in the tank. The vapors are filtered through a charcoal canister that sometimes resides under the hood, but the more recent trend seems to be to put them closer to the fuel tank. If that system is malfunctioning, it could be venting tank vapor and that would cause your smell.

Just catching up on reading and noticed this.

This isn't quite how it works - mostly true - but not entirely.

The canister has three ports: Load, vent and purge. Since 1998, passenger cars have had to use an "On-board Refueling Vapor Recovery" (ORVR) system. Some of you remember the vacuum bellows that used to be on gasoline dispensing nozzles - that was to catch vapors (fumes) while you were refueling - and stored onsite at the station. Well... Oil companies have more lobbyists than auto makers, and it was decided the auto manufacturers would be responsible for catching vapors while refueling. :blankface:

So - now, we use skinny fill pipes, and an assortment of valves that create a vacuum at the filler neck when you pump gasoline into your car. The vacuum pulls surrounding air and any vapor generated into the tank. This creates a positive pressure in the vapor dome (area above the liquid fuel) of the tank. This pressure escapes through the canister which is filled with activated carbon; the carbon attracts the fuel molecules out of the vapor and vents fresh air out of the vent port. This way, hydrocarbons are trapped within the canister and not out into the atmosphere.

The volume of the canister is limited and can only hold so much hydrocarbons, so it is sucked clean - or "purged" - when the engine is running. You can't just always pull a vacuum on the canister: After a refueling even, there's enough fuel available through the purge system to run the engine - with the injectors turned off! So, there is a valve that purge flow is limited with, and the normal / failed state of the valve is in the closed position. I.E. It cannot cause a fuel smell while the engine is off.

Now, one thing that could cause it (besides PCV) could be a leaky injector. So, shut off the car, there's still high pressure in the fuel rail. It is possible for an injector to leak fuel as the engine sits. The fuel vapor can actually migrate through the entire intake system and exit the intake snorkel. I know this had to be a concern for GM - just because of the carbon pad that is in the stock airbox. That pad is a "bandaid" to prevent fuel vapor from escaping the intake system.

 

[MPFab]

Thanks for correcting that.

 

[Scot]

Thanks for correcting that.

No problem. I've had my hands in a few different OEM designs - and got to do all the "fun" witness testing of the systems in California with CARB back in 96 & 97.

Sacramento, CA is pretty awesome in February if you're a Michigan resident.

 

[ChrisJ]

Just catching up on reading and noticed this.

This isn't quite how it works - mostly true - but not entirely.

The canister has three ports: Load, vent and purge. Since 1998, passenger cars have had to use an "On-board Refueling Vapor Recovery" (ORVR) system. Some of you remember the vacuum bellows that used to be on gasoline dispensing nozzles - that was to catch vapors (fumes) while you were refueling - and stored onsite at the station. Well... Oil companies have more lobbyists than auto makers, and it was decided the auto manufacturers would be responsible for catching vapors while refueling. :blankface:

So - now, we use skinny fill pipes, and an assortment of valves that create a vacuum at the filler neck when you pump gasoline into your car. The vacuum pulls surrounding air and any vapor generated into the tank. This creates a positive pressure in the vapor dome (area above the liquid fuel) of the tank. This pressure escapes through the canister which is filled with activated carbon; the carbon attracts the fuel molecules out of the vapor and vents fresh air out of the vent port. This way, hydrocarbons are trapped within the canister and not out into the atmosphere.

The volume of the canister is limited and can only hold so much hydrocarbons, so it is sucked clean - or "purged" - when the engine is running. You can't just always pull a vacuum on the canister: After a refueling even, there's enough fuel available through the purge system to run the engine - with the injectors turned off! So, there is a valve that purge flow is limited with, and the normal / failed state of the valve is in the closed position. I.E. It cannot cause a fuel smell while the engine is off.

Now, one thing that could cause it (besides PCV) could be a leaky injector. So, shut off the car, there's still high pressure in the fuel rail. It is possible for an injector to leak fuel as the engine sits. The fuel vapor can actually migrate through the entire intake system and exit the intake snorkel. I know this had to be a concern for GM - just because of the carbon pad that is in the stock airbox. That pad is a "bandaid" to prevent fuel vapor from escaping the intake system.

Holy crap.

So as you know in NJ we are not allowed to pump gas I assume because we're retarded or something, that's another subject. Anyway, I assumed they still had those bellows on the gas nozzles here that vacuumed up vapors? Maybe I'm mistaken?

What creates this steady pull without the engine running?

 

[Scot]

Before ORVR, fuel filler pipes were 2"+ in diameter, so fuel would run down the tube like water across the bottom of a pipe - that is, there was a free air space above the fuel that vapor could travel upward out of the filler neck.

Nowadays, the filler pipe is a much smaller diameter, around 1". What this does is allow the gasoline to come in 360 degree contact with the pipe. The flow isn't laminar (solid flow of liquid, always touching 360 degrees of the pipe), so there are voids / pockets of air that get trapped every time the fuel makes a 360 degree contact with the pipe. These entrained pockets of air cause the vacuum - as one pocket of air gets trapped and goes rushing down the pipe with the fuel, that volume of air is replaced by one that was farther away. Sped up many times to "real" speeds, you have a constant flow of air getting sucked into the filler neck.

The bellows used to vacuum up the vapors, but haven't been necessary since ORVR systems were mandated. If you see nozzles with bellows, they're probably old and not working.

 

[sonichead94]

So i read through this thread cause i got the same problem. Theres oil on the outside of the turbo and inside. But its no way near as much oil the guy posted in the last post. Theres also oil around where the big nozzle is connected to the IM but its not as much. still bad though right? I've heard people replacing there turbo cause of this and it still smokes. seem's like the problem is the checkvalve, if so mayb replacing the IM might resolve the smoke issuse unless theres a way to fix that checkvalve.

 

[Chevrolet Customer Care]

Hi sonichead94,

I'm sorry to hear that you have been experiencing this concern with your Sonic. I cannot guarantee anything, but I will be glad to look further into this for you. Please feel free to send us a private message with your full contact information, VIN, current mileage, and dealership name if we can be of any extra assistance. Thank you.

Kristen A.
Chevrolet Customer Care

 

[mja]

Looking for a little help getting some info for the first mod to my sonic 6spd 1.4T hatch. Ordering a Saikou Michi oil catch can (OCC). They need to know the size of the PCV tubing, and if there is a crankcase vent tube before the FMIC since most turbo setups use two OCC's when set up properly.

Attached are some pics of the tube, and my best guess is 1/2"-5/8" tubing, but don't want to cut into this thing prematurely.

And where is the crankcase vent tube if there is any?

Thanks!

 

[Preloader]

There is no vent tube. This is a closed PCV system. All of the crankcase gases are pulled into the intake during vacuum or sent to the inlet side of the compressor during boost. Refer to my hand drawings in post #1 of this thread.


I can't confirm the PCV line size. It's covered in corrugated plastic, but appear to be 5/8".

 

[mja]

There is no vent tube. This is a closed PCV system. All of the crankcase gases are pulled into the intake during vacuum or sent to the inlet side of the compressor during boost. Refer to my hand drawings in post #1 of this thread.


I can't confirm the PCV line size. It's covered in corrugated plastic, but appear to be 5/8".

Thanks preloader, a single OCC makes this cheaper, with more room on the firewall for future goodies

 

[Preloader]

A few members have installed catch cans here. The forum's search engine is pretty lame, but if you go to google and type in:
sonicownersforum oil catch can

You'll get results. I'm not familiar with the brand you mentioned, but be sure that it's a quality can with an actual baffle. The cheapo $60 eBay ones are worthless and belong in the garbage catch can.

 

[mja]

Looked up a few threads on this, here is the company I'm ordering from: Saikou Michi Co. 2013

So far they've been helpful and patient making sure the measurements are correct and what options are needed, they custom make most of their cans to fit each vehicle. Going with matte black color to match all the engine bay plastic. The goal is to look like a factory install.

 

[SuperSonicRS]

DDM is working on a OCC for our cars, I'll be waiting for theirs to come out.

 

[cokegarcia]

Ive a persistent P1101 (cleared maf, check intake, etc) and found a bit of oil on the top pcv, would you bet its the hose?? Its the only oil on the motor all other is dust.

Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

 

[Sonic HB]

so catch can?

So what is the bottom line .. should i get a catch can for the oil i have the 1.4 turbo?

 

[carbon02]

Where to start? I think it's best to explain the entire theory because it makes it easier to understand a system when you know what it's suppose to do/



Why is positive crankcase ventilation necessary?

Well the biggest reason is blow-by. Heat expansion coefficient dictates that the piston rings must have a small split in them to allow them to expand when they experience rapid changes in heat.

The crankcase isn't actually entirely sealed from the cylinder where the combustion takes place. As the piston comes up on the compression stroke, some gas/air mixture will always be allowed to "blow-by" the ring gaps and enter the crankcase. Also combustion blow-by occurs during the combustion stroke.

The PCV system is designed to not only actively remove those hydrocarbons from the crankcase where they will rapidly compromise the engine oil's integrity and attack gaskets and seals, but also it is designed to return those gases back into the cylinders in an attempt to burn them, rather than release them into the environment as emissions.

You can read about the history and how it was actually GM that first instituted the system for widerange in civilian vehicles by searching PCV on wikipedia.


A traditional PCV on an N/A engine is quite simple and effective. Fresh air is allowed into the crankcase, and since the intake is almost ALWAYS under some vacuum..... that vacuum is allowed to pull that fresh air through the crankcase removing the volatile hydrocarbon blow-by with it. A one-way or check valve is used to prevent any pressure or fuel mixture from backfeeding through the PCV. This is the PCV valve most of us are accustomed to.



Now we come to turbocharged engines and are faced with a new obstacle....
Boost.

When the intake is no longer under vacuum, but instead boost pressure, a checkvalve would close and stay closed for the duration of the time boost is occurring. ALSO, boosted fuel mixture has a much greater probability of blowing by the piston rings.

As a result, most PCVs on turbo'd applications, have a more complex two stage system. A vent for idle and low throttle operation, and a secondary vent for WOT and boosted operation.

There are a variety of styles used, but I'm just going to jump straight into ours.

Our PCV on the LUV/LUJ draws crankcase gases through the intake manifold (IM) through a port in the center between the two middle intake runners.

The crankcase gases exit the case through the head. The head collects the gases from block directly and also through passages in the valve cover.

Here is where the gases leave the head and enter the IM:

Here are some of the passages it collects vent gases through:

Now to explain the two processes. The first is the PCV during idle and part vacuum, like mild throttle situations and cruising.





(please laugh at my elementary drawings..... I lol'd)



This is a good time to show a close up of "checkvalve" in our PCV. Looking up the PCV runner in the IM from the view of the gases leaving the crankcase, you encounter a bright orange orifice. This orifice allows gases to be "pulled" into the intake path and essentially burned with the fuel mixture.

This portion is pretty consistent with a traditional PCV system. But now let's see what changes when you dig into the throttle and create boost.

WOT

(laugh it up)



Now the IM is pressurized, and that little orange "diaphragm" is pushing against those little holes. That stops boost from escaping back into the crankcase, but now the crankcase gases need a new exit.

Look again and notice the port at the top of the IM before the orange check.

That is this big nozzle:

It runs via a tube directly to the inlet of the turbo compressor:



There is a considerable amount of suction coming from the compressor, and that is what pulls the crankcase gases (which are substantially greater during high RPM boost) from the PCV.

I hope that was comprehensive. I've wanted to do this write-up for a while because the PCV comes up a lot in troubleshooting discussions. Especially when it comes to "puff of smoke" problems.

I expect that topic to be addressed soon, but this thread can be references where PCV is concerned.

Preloader-

There' several tech's over at the Cruze forum who have stated that GM now has a procedure to check for the orange check valve in the intake if a car comes in with the "rupture disk" in the valve cover blown. I guess it's repair of the valve cover, and possible inspection/replacement of the intake.

The problem I have is understanding what a person would visually see looking down the big gas outlet connection with a flashlight while the manifold is still on the head.

If you still have the intake, could you comment can you see the orange "check valve" if it's closed by looking down the big exhaust collection port from the outside of the manifold looking down?

If there's no orange noticeable then maybe the check valve is either stuck open or missing?

You're the only one that I know of that has snapped pics of the intake off the engine. If you could comment as to what is seen looking down the port with the check valve closed vs open that would be great.

There's no alternative for a new intake other than the GM one that comes loaded with the fuel rail and the throttle body. This is going to be a big expense for a lot of us, as the 5 year powertrain warranty runs out.

Any first hand thoughts from a guy who understands the theory would be great!

Thanks-

Carbon02

 

[BradF80]

2 things.

1)The PCV system in this car is overengineered. I would bypass 90% of it and create a NEW PCV setup, with it's own PCV Valve; bypassing the intake garbage. Just screw a Bung into the valve cover for a PCV hose and run it to the suction side of the intake. Install a catch can. Problem solved. Running the PCV through the pressure side of an intake with that tiny diaphragm as the barrier is utterly stupid.

2) OIL - The recommended service intervals on this car are ridiculous for the type of crap oil they put in it. The biggest issue I see people have is with oil. (i.e. leaky turbos) . I believe this is attributed to the extended oil change intervals on conventional oil. Semi-synthetic is like 5% synthetic oil. There's no way it extends the oil life that significantly. Run synthetic; do oil changes every 4,000 miles; and I bet you never see an oil problem with your turbo.

 

[Kcmo83]

Any write ups on a aftermarket breather for this pcv? Specifically for the 1.8?

 

[Kcmo83]

I dont have the turbo, but the 1.8 this is a good write up. Do you guys think its a bad idea to run this breather i got with my kit? I installed it at the end of the pvc line and plugged the hole on the throttle body . Noticed that oil does seep down this line to the TB, so by using a breather im letting gasses out but not letting oil into my intake, which is probably why they say its a racing application . Any input would be appreciated

 

[Kcmo83]

No imput? Sad face.