what is a PVC valve and does it need to be change during a tune up?does it harm anything?

 

Positive Crankcase Ventilation


The purpose of the PCV valve is to prevent unburned hydrocarbons and carbon monoxide, present in blow by gases, from being expelled into the atmosphere. This process also helps to reduce moisture and the presents of corrosive gases in the crank case ,which extends the life of you engine and engine oil by keeping it cleaner longer.

Start the engine and let it idle. Place your thumb or finger over the open end of the PCV hose to feel for a vacuum(suction). IF you don't feel a vacuum you need to check the hose for clogs or other blockages for example a sharp kink in the hose. If need be just replace the hose with a new one.

I dont think I have ever had to replace one on any of my honda's





[Modified by EneMy X, 9:10 AM 6/11/2002]

 

It's an emmissions thing. Keeps the atmosphere cleaner, but makes the engine run dirtier and less efficiently.

 

WRONG.

 

Really ? Then could you be so kind as to explain why and how a PCV system can benefit a motor ? I would like to read how a venting system for noxious and corrosive gases being circulated back into your combustion chamber is a good thing (aside from emissions).

Please enlighten us ! That would be great...

 

i think X2board might be correct. ON A SMALL SCALE, the valve could actually lower your engines performance (were talking at most probably one HP) because you a diluting the oxygen in the air intake with hydrocarbons etc. Mostly It just helps to lower emissions though

 

i know if the valve is stuck closed that oil could leak past your distributor o-ring and get inside of you cap. i think its connected to your intake so that it can use the vacume to pull out the "hydrocarbons" instead of trying to let it vent out with pressure.

 

Don't forget... small things in motors have large effects.

The PCV system is a one way valve that functions based on the vaccum in the manifold. Manifold vaccum keeps the valve partially closed at idle and will open relative to vaccum. As the motor turns faster and produces more power (burns more air and gas) The lack of vaccum opens the valve more, allowing more crankcase gases to enter the manifold. The more mixture you are burning, the more gases can be vented without affecting the mixture quality on a large scale.

The gases emitted by the PCV system into the intake stream are flammable, but can affect flame propagation during combustion. This system pollutes the mixture, causing a small loss of power during the combustion process.

As you would notice, our cars run a closed loop PCV system. While good for emissions, this system, performance wise, is less effective than an open loop system that draws air from the outside (ie: valve cover breather). For proper vehicle operation, it is necessary to run some type of venting system, but a PCV does harm and not help the situation. And, yes, if the valve is stuck closed, it will evnetually cause oil to enter the intake manifold through the IM tubing.

PS, as you increase power over the stock ratings, the PCV system becomes more and more ineffective and may even damage the valve itself over time... impeding the vehicle performance even further.

X2


[Modified by X2BOARD, 2:10 PM 6/11/2002]

 

So what happens when the pressure becomes positive in the intake manifold to the PCV system (example: a turbo)? I would assume the valve would be open (since the lower the vaccuum the more the valve will open)....but the positive air pressure would actually close the valve from above right??? WIERD.

 

The valve is vaccum controlled...
To clarify a bit... When the motor is idling, vaccum is at maximum, which keeps the PCV valve mostly closed. As vaccum decreases in value (approaching atmospheric) The PCV valve is allowed to open (relative to consumption) So the larger the amount of vaccum, the less the valve allows to be vented from the crankcase. Excessive crankcase pressure would promote blowby (in the wrong direction).

BTW, forgot to mention... if you have a PCV on your car and have it connected properly... you need to replace the valve every 15-20K or so if you want to keep everything in tip top.

X2

 

you don't want breathers, you want to keep the stock system. the stock system creates a suction that a breather would not.

 

True, unless you are converting to a full open loop... keep the stock PCV in place or it will impair the car's performance

 

Right...but if the pressure becomes POSITIVE in the intake manifold...What would happen...I guess it would remain open then. Since the vaccum must PULL the valve closed...so the less the vaccum pressure to hold the valve closed...the more the valve opens. So assuming what I just said...when you hit POSITIVE pressure...the valve should be completely open...and functioning in the opposite direction since the positive air pressure should be forced INTO the PCV valve as opposed to OUT of the PCV valve. How's that for emissions????

 

As far as positive manifold pressure and emissions... they don't mix well. The only way you will see positive manifold pressure is when you pass atmospheric. N/A cars cannot pass atmosphereic, even under full throttle... unless you have the 'Tornado' HAHAHAHA... (not an ad... don't buy the Tornado)

The only way to create positive manifold pressure is to add some type of FI, like a turbo or supercharger (not nitrous). An FI application would prolly damage the valve's spring, or at least weaken it. Due to the fact that the car will periodically operate above atmospheric, the valve would still work at the limit of the spring tension. While in boost, the valve would supply the maximum venting to the manifold, this would not necessarily upset the system much, but the crankcase would have more gases to vent. The small PCV valve that's designed to operate withing specific non-boosted (on Hondas) parameters would not be able to vent enough gasses to keep the crankcase properly ventilated. In addition to this, due to increased crankcase pressure, it is possible and likely that small amounts of oil would be spit out with some of the gases (oil in your IM isn't good). This is why it is necessary for turbo or supercharged cars to run a full open loop PCV system. This is typically done by using a Catch Can set-up, bypassing the PCV valve completely.

A catch can system employs a breather filter for fresh air (yes, breathers ACTUALLY serve a purpose) and a line running from the venting portion of the stock PCV system to a can with a large filter. The can 'catches' excess crankcase gases and any oil that is spit out with it... the gases escape thru the filter on the can. A typical catch can setup will trap about 1 or 2 cups of oil between oil changes. *Yawn* It's early and this was long. Anyways, I prefer not to have all those tainted gases in the IM anyways...

I speculate that since the gases eminates from the crankcase, they should be quite hot, and as we all know, a heated intake charge reduces Tq and Hp, so removing the PCV system should also reduce intake temps slightly and thereby reduce the chances of detonation.

X2

 

Anyone here running an open loop PCV system?? Anyone have instructions or pics? Thanks.

 

My PVC valve broke and it sucked the oil out of the engine. that was with 100k on it. I was driving down the road and the oil light came on. It was so low it wouldn't even show up on my stick. Got it fixed and no problems as a result

 

One correction to note. The PCV valve is operated by vacuum pressure (as mentioned above). But the valve is opened by vacuum and as the vacuum increases the valve opens more. The weight of the plunger and a spring closes the valve (and the lack of vacuum).

Here is a diagram from the Helms manual which illustrates the PCV system and gives a brief description.



Larger image (may have to cut and paste): http://www.imagestation.com/picture/...d.gif.orig.gif

 

How do you get the PVC valve out? I tried pulling lightly on the valve but it wouldn't come out. I was scared to break it off? Any suggestions?

 

Actually, vaccum decreases with increased engine speed. The spring opens with less vaccum and closes with more.

 

volcom, you sure you're grabbing the right thing?

just pull, sometimes the rubber around it gets a little sticky with the oil/etc. It should pop out.

 

I still disagree and here is why...

"Normal Engine Operation

At idling speed, an engine at sea level should show a steady vacuum reading between 14" and 22" HG. A quick opening and closing of the throttle should cause vacuum to drop below 5" then rebound to 23" or more. "

"Starting with the engine at idle, slowly increase engine speed to 3,000 RPM, engine vacuum should be equal to or higher than idle vacuum at 3,000 RPM. If vacuum decreases at higher engine RPM's, an excessive exhaust back pressure is probably present."

This was taken from http://autorepair.about.com/library/.../aa112401a.htm

 

I have to interject, first, some academics

it is PCV not PVC, pvc is a type of piping tool and PCV is the system of crankcase ventalation.

next, a vacuum is completely devoid of air, it is not the best word to use. say manifold pressure and atmospheric pressure, or MP and AP. much more suitable to cars than a vacuum.

now, on to what I was taught in school, at idle and constant engine speeds you have low manifold pressure. when you place your engine under load the MP drops, the higher the load the lower the MP as compaired with AP. when you are at WOT, or accelerating the MP will increase. this creates the whole basis for a MAP sensor (manifold air pressure) and determines how much load is on the engine, or how much you have mashed into your throttle based on the MP as compaired with AP.

try to think of it like when you are sucking coke through a straw at mc donnalds. take your finger and squeeze the straw, still sucking through the straw, the pressure will drop on the side of the straw that is closer to your mouth, and the pressure will remain constant on the side that is closer to the coke, the harder you suck (create load) the lower the pressure will go on the side of the straw near your mouth. now, partially squeeze the straw, and suck harder, if you do it at the same rate, compaired with how much you squeezed the straw the first time, you will have the same difference in pressure. now, open that bad boy up all the way, and start to suck really slow and then suck harder and harder through the straw, until the straw has reached its maximum flow capacity (which i doubt a human can acheive, although I know some girls who would probably push the limits to the end) the pressure inside the straw will always be whatever the ambient is for the coke, until the straw reaches it's maximum flow capacity. does this make any sense at all?

 

Actually, PVC is polyvinyl chloride, which a type of polymer. JK, I am being a smartass.

 

semantics (I know I started it)

 

that would be the hose that goes from valve cover back to intake right ?

so what do you do with it, in order to prevent carbon build up, etc ?

i've seen people have small filters .. no good ?