Just wondering.My 1987 dodge ram has been running kind of rough lately, but only certain times and than it would run OK.
So i tried a shot in the dark..i replaced the pcv...so far so good but it is too early to tell.
The old pcv has oil and carbon deposits all over it.

A "bad" PCV valve is either cracked or plugged. If the valve has no visible cracks in the housing, and the check-ball still rattles when you shake it, the valve is OK. If nothing happens when you shake it, spray it down with carb cleaner (from both ends) until you break the ball loose. Shake, rinse, and repeat until the ball is free to move. You now have a "good" PCV valve...unless the housing is cracked

In regards to your truck running poorly, look for broken/cracked vacuum lines, and replace any that look suspect. Vacuum leaks wreak havoc on your ignition.

-S/6

I dont totally agree with Super6 on this.

Basicly what the valve is ment to do is make a "controlled" vacuum leak. Basicly at times of High Vacuum(Such as Idle) the valve is closed so only a small ammount of flow is allowed threw the valve. Time of lower vacuum(Floored.. hehe) the valve lets more flow threw the valve.

How to test:
Shake valve, if no rattle its bad.
While the valve is connected to the Carb via the hose and the engine running pull the valve out of the valve cover. using a finger to feel the flow, should be hissing sound with small flow. Cap hole off the valve should make a little clunk feel from the valve reseting. If it does not do these things then the valve is bad.
As Super6 said If the housing is cracked its bad as well.

I suggest if you have a valve just get a new one. They are cheap and its just a good idea. The rattle test, only tests to see if the valve is free and hasnt got locked up. inside the valve is slug and a spring. the Springs can rust or break and the seat in the valve can get screwed up and allow the valve close all the way..

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Mike C
http://cuda.iclownz.com
67 - Barracuda Coupe - 225 - Automatic

well, I'm not agree neither with michael cuda or super six...

now seriously, the pcv valvle controls the flow, so even if it's working and it's dirty inside, some roughness can happen. Basically, if yojur PCV is allowing less air amount into the carb, the idle rpm range will go down and "cranky" (rattle, roughness) but you wouldn't feel nothing once you reved up. If for some reason the valvle is allowing too much air to flow inside the carb, the idle will rev up, and when you try to accel you'll notice some sort of almost stalling feel. it will cough and sput and then run.

PCV works on the lower RPM side, on the high vacuum side, the vacuum coming from the intake opens the pcv ball sucking crankcase fumes, then at higher RPM range, when the vacuum inside the intake lowers, the spring and ball locking mechanism works and closes the line.

I can imagine that you may be getting dizzy with so many kinda diffrent answers but you did the right thing. Also, check your lines! that's a good idea!

Thanx guys...the old pcv rattles a bit, but not as much as the new one.
So far i haven't had a problem, which leads me to belive it is either a coincidence or the pcv was not the best.

I've had PCV valves go bad before. The symptom was the engine would run good, next light run real slow and rough the run fast and rough at the next light. Went to Pep Boys spent a couple of bucks and it is fixed with a new PCV valve. Also make sure the hose from the PCV isn't collapsing. I had that probelm too. I fixed that by taking a piece of 3/8 in steel line and put a small piece of hose on each end for the PCV valve and carb. No more collapsing hose. Also make sure the port on the base of the carb isn't plugged up. That will also cause problems.

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Former bent 6 owner
Mark

PCV flow is not related to rpm, it's entirely controlled by vacuum.
At idle, cruise and trailing throttle (high vacuum), engine vacuum is strong enough to overcome the return spring and pulls the tapered end of the internal cone into the opening - partially closing it.
At WOT (very low vacuum) the spring is stronger than vacuum, and forces the restrictor cone away from the large orifice and INCREASES flow through the valve.

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I replace my PCV once a year. That way there are no worries about whether its bad or not.

What Panic said was 100% correct, and I was trying to express the same thing, which he was able to do better.

The reason the system works like this is because at idle and times of high vacuum there isn't much blow-by as there would be when you apply gas, which makes the vacuum drop. The whole system is designed to get rid of Blow-By and pressure of other sorts. I have heard people say "My Engine is great shape I don't have any blow-by" This is untrue even the best engine has a very small amount of blow-by. Keep in mind when you get down to it there is 3 rings which have small gaps in them that are meant to keep the explosoin contained in the Cylinder.

I have had the colapsing hose problem my self. The reason I think this is caused by replacement hoses. Mopar called for 11/32nd HD Vacuum hose, I havn't even seen replacement hose this size? So almost everyone uses 3/8 hose, when I changed mine out I noticed how much smaller the walls are compared to the old stock hoses.

Almost every time I replace a PCV valve I make sure to clean the hose and the port going down into the intake manifold. The nature of the system it gets junked up real quick and easy, this is why companies want you replace that valve to often. Also don't over look the PCV grommet on valve cover, these get hard and wont seal anymore.

As for Ill effects of a bad PCV system, I don't know much about that end, I have never really had a car that ran bad with a plugged system, I do know it happens.

I do as Eric says... When in doubt change it, they are cheap =)

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Mike C
http://cuda.iclownz.com
67 - Barracuda Coupe - 225 - Automatic

Ok, I may be wrong

But, in order to learn something by reasoning it... why is that when you have a bad engine (too much blowby) this sistem (PCV) kinda "chokes" your carb? I've experienced this in many busted /6's. When you have too much blowby, idle revs up, and when you try to accel the engine will kinda stall for an instant, cough and burp and then go. It's almost imposible to set a right idle speed with PCV connected on a bad engine. That's why I thought that PCV works "reversed" than you guys sez that works... clue me in, please.

What causes blowby?
And how is it fixed?

Blowby is caused by excessive leakage past the piston rings. A PCV value works as a controlled vaccum leak. With excess blow by, that controlled leak has changed dynamics and is not working within the original design parameters.

The way to fix this is to bore and re-ring the engine.

I would suspect the reason they rev up is because due to the engine being shot your gonna have a low manifold vacuum, so the PCV will not close as much as needed making a large vacuum leak and as you well know vacuum leaks will rev the engine =P

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Mike C
http://cuda.iclownz.com
67 - Barracuda Coupe - 225 - Automatic