Confused: PCV operation???

Hi everyone

i just got new pcv valve and got absolutely confused with it...

what exactly does PCV do? coz i thought it lets the oil vapours go from engine back to intake... but actually it does opposite thing, it lets the air go into engine!!! the more air flow the more air goes into engine!

so what is it for ? and does it work the way i described???

[svx_commuter]

One Evil one NO. It allows the crank case vapor to flow into the intake manifold (normal flow). The PCV valve screws into the intake manifold after the throttle plates. This where the intake manifold vaccum is highest when the engine is at idle. The intake manifold pressure is normally lower than the crank case pressure. There is a check valve in the PVC valve that prevents high pressure in the intake manifold from entering the crank case (reverse flow). In my opinion, if the engine never backfires, the check valve is not needed.

Is your new valve made backwards?

ok the reason why i got new pcv valve that the car had the phenomenom called "dipstictus erectus" ... which is indication of bad PCV operation

ok so i went to subaruparts.com and checked if i got the proper one... ok there is a pic there and what is PCV is called Air control valve (#11810AA000)
thats what i got... looks like PCV

anyways what im trying to say that the air (vapours) can go only from tube side to side where the PCV is screwed into manifold ...and not backwards...

ok so if its screwed into the manifold, and the pressure there is lowest, then the air goes into where the PCV is screwed into....

ok makes sence...but!!! what goes throught that PCV hose? The hose is attached to some plastic thing at the other end, with another hose which goes from the black intake box...

dont understand that at all ..whats the point?? coz is not it supposed oil vapours go through the hose... from engine back to intake to get burnt?

in addition my car iddles bad... and at the moment no PCV hose... as old cracked and hard as stone

waiting for ur clever answers

Thx

and in addition

if the PCV is ok but dipstic still "erects" what else can be wrong?

[Mr. Pockets]

Well, a cracked (or missing) vacuum hose of any kind is going to make your car idle poorly. Replace that hose and you'll probably be good to go.

http://www.subaruparts.com/diag/?mod...category=082-A

for ppl who understand: on this picture

hoses 1 and 7 are attached to connector, right?

the the connector has 4 hoses, 1 from intake box, one from PCV itself, and 2 from somewhere i got absolutely no clue where...

lol

so where the hoses 1 and 7 come from? should they be vacuum hoses? as well as all other hoses?
vacuum oil resistant? or just oil resistant? if one of hoses got crack or missing... what should i get as the result?


cheeers hope u guys can unswer my questions

hmmm how bout bad iddle? missing psv hose, bad hoses 1 and 7...



bad idle for last hmm 3 months....woundering around here what it can be....

khe khe ok, ill do the replacement this week and hope will get written off from "rough idle SVX club"
figers crossed

[Mr. Pockets]

Originally posted by 6evil9
khe khe ok, ill do the replacement this week and hope will get written off from "rough idle SVX club"
figers crossed

I think, if you replace the missing hoses, your car will idle just fine. If it doesn't, keep looking for other cracked or missing hoses.

I had a hell of a time fixing my wife's 1990 Legacy. It had a rough idle - it actually loped up and down between 2k RPM and, well, stall. In the end, it was a broken T-connector which, go figure, had three different size hoses plugged into it. WTF? So of course I had to buy that from the dealer. I bought the hoses which plugged into it for a total of $50 for some molded rubber. Argh.

Anyway, the moral of the story is that your PCV system should have no leaks. Otherwise you'll have rough idle, no brake assist, etc.

Speaking of no brake assist, that happened a lot to my wife's old Exploder. Every so often, when starting, it would blow hoses and caps off a big vacuum junction. This happened one time at the most inopportune moment - when she had a bunch of her students in the car for a field trip. Private school, don't ask. Anyway, starting blew the brake booster hose off and the leak caused the engine to lope. Being an automatic, this meant that the car lurched badly at idle, and with no power brakes she had a hell of a time keeping the thing stopped at a traffic light.

We can laugh about that now. I ended up putting zip-ties on all the vacuum hoses I could find. Problem solved - her dad still has the car.

[svx_commuter]

Hoses 1 and 7 run to the top of the valve covers

Check all the hoses for cracks as Nick said and replace them. It could even be one of the same hoses connected to the manifold or a loose manifold.

Why are you so evil?

ok still main question is not answered

why is PCV there anyway? and why to have hoses going from valve covers?

where the crank case is then? any good explanation of what happens there?

thx

about bad hoses, i got that idea long time ago, i replaced couple of hoses from vacuum line, still trying to find the rest...as its bloody hard in this country

[qoute]
Why are you so evil?
[/quote]

Am i evil?
uh huh its just the way it is, i guess
we all gotta cope with that

[Mr. Pockets]

Originally posted by 6evil9
ok still main question is not answered

why is PCV there anyway? and why to have hoses going from valve covers?

Sorry. Here's a good description of what the PCV system does:

http://www.hastingsfilter.com/engine...tsb_94-2r.html

cheers man

ok last questions... are hoses 1 and 7 oil resistant? or just vacuum hoses? why are they there?
and what kinda hose from black intake box to the plastic connector (with hoses 1 and 7 are connected to)

thx

[Mr. Pockets]

I'm not sure what you mean by 'oil resistant,' but they are vacuum hoses, yes. Since they're taking vapors right from the inside of the engine, I think they can withstand some oil without deteriorating.

I do know that they're not ATF-resistant. The situation in the above (rambling) story about the Explorer was the result of a bad valve in the transmission, of all places. It was a diaphragm actuated with vacuum pressure from the engine. When the diaphragm was compromised, it allowed ATF into the PCV system. The hoses all sucked it up, expanded, and started flying off their connections when the car was started.

In the end, they're just rubber hoses. They break down, tear and crack over time. It happens and there's very little you can do about it.

But you don't need to get the molded hose from the dealer - you can get the same diameter tubing and cut it yourself. If you're unsure what diameter hose you need, you can take the fitting it connects to into an auto parts shop and get a piece of tubing to fit.

I hope I answered your questions. I can see you're getting frustrated by my poor explanations. Sorry about that.

[oab_au]

Gid'ay Sergi, I think we have had this conversation before.

The way the PCV valve works is in two stages.

First when at idle or cruse, the engine fumes are drawn up through the PCV valve to the inlet manifold to be burnt. In this stage the air is drawn from the inlet air box through the two hoses (1,7) into the sides of the motor, this air flows through the inside of the motor,( called the crankcase) up through the PCV valve to the inlet manifold, to be burnt. Air also is drawn through a hose (3) from the air box to flow through the PCV valve.

The second stage is when the throttle is wide open. In this stage the PCV valve is closed, so the fumes and pressure in the engine(crankcase) go the opposite way. From the engines crankcase through the two hoses (1,7) to the air box, through the throttle body to be burnt in the engine.

The only hose to have vacuum applied to it is the hose from the PCV valve to the inlet manifold (6) this is the one that may leak air into the inlet manifold to cause a bad idle. All the other hoses just carry air.

Harvey.

[Mr. Pockets]

Thanks for that detailed explanation, Harvey. According to your description, and looking at Sergi's posts, it seems that he's probably missing this hose from the PCV valve to the inlet manifold.

Thanks again!