Yes, that is correct.

In a somewhat related story, back in the 80's when I was at Chrysler, in 1981, Lee Iacocca took one of the first production Imperials, (which had a continuous flow fuel injection system, one of a kind in the automotive industry, designed by Huntsville Division, the same division that built the electronics for the Apollo Missions for NASA) and took that vehicle to show off to some of his industry executive friends. Lee had opened the hood to the splendor of these executives, with it's absolute rock stable idle, and huge Mopar air cleaner top and it's glistening chrome cover, one of the executive spins the wing nut off, and proceeds to lift the lid to see this injection in action, and the vehicle huffs and puffs, and promptly stalls. Everyone looks over at Lee with wonderment, and asks, "what happened? It shouldn't die like that!" What they didn't know is the vortex flow sensor was cut off by the lid being lifted, and the fuel rails shut down. Iacocca who was embarrassed by this, (and you didn't embarrass Lee) called engineers the next morning and had them place a ringed clamp to be placed around the air cleaner top so that would not ever happen again inadvertently.

Moral of this story is, if it idles good, all is well, leave the wing nut alone and stop asking it to do things it was never intended to do in the first place.

 

Thanks again, David.
So basically (again, please correct me if I am wrong) what you are saying is that the spring holds the valve fully open and the degree of vacuum created by the inlet manifold acts (via the diaphragm) against this spring to close it? That I can understand!

However, this 'metering' that can drastically affect my fuel trims is controlled by a simple spring? So, in reality the only way to KNOW that (say after 100,000 miles) the spring has retained its youthful vigour is to replace the valve with a new one?

Regards,
Ray

 

Ray, you're making much more out of this than it really deserves. If you feel you wish to replace the PCV valve as part of routine maintenance, then by all means, do so. Good luck with your vehicle.

 

Thanks David. I appreciate your experience and help. I am obviously overestimating the importance of this valve to my fuel trims.

 

David, apologies for drawing you back to this old thread, but please confirm that I had it 180 degrees out when I stated you were saying that the vacuum applied by the inlet sucks the diaphragm against its spring to open the valve - It is in fact the vacuum applied by the inlet that sucks the diaphragm against its spring to close the valve - Hence at idle with high vacuum, spring is overcome and valve is closed, whereas WOT with very low vacuum equals spring holding valve open to allow maximum flow of crankcase gases?

Do I have this right at last!?

I ask because someone has suggested that a 'sticking' PCV Valve could be causing the huge clouds of grey smoke I occasionally (and erratically) get from my exhausts?
Regards,
Ray

 

David, Michael - Okay, I think I may understand how the PCV works at last (thank you for your patience) - The high vacuum at idle sucks the diaphragm down against the spring and closes the valve. The spring then overcomes the weak vacuum at WOT and opens the valve.

What about the other bank? Surely there is no barrier to oil--rich crankcase vapours being introduced directly into the TB? Obviously something must monitor the amount of these vapours for fuel trim purposes, because they are introduced after the MAF?
Aren't the spark plugs going to hate all this oil from both breathers being mixed in with the air/fuel they are supposed to be igniting?
How does burning oil lower emissions??
Regards,
Ray

 

The entire crankcase is ventilated by the single PCV system. Fresh air is drawn in from the left hand side (pipe to the air inlet duct), pulled through the cam cover, crankcase, other cam cover, and through the PCV valve into the throttle body. The crankcase fumes are already taken into account by the PCM and shouldn't significantly contribute to fuel trims.

Modern engines have much better rings and valve seals, blowby and oil burning through the PCV shouldn't be enough of an issue to cause problems with spark plugs or cat converters (in theory). It certainly can, if the seals are leaky enough. The oil residue inside the intake manifold is usually from the PCV system. I believe oil catch cans were recently discussed on this section.

I recall a Mustang friend telling me there were slight issues with oil smoke on startup if the engine was start/stopped without running long. Some of the Cadillac Northstar engines would loose their PCV baffle and start sucking way too much oil into the engine, blowing lots of smoke.

 

Thanks Michael. I now understand how the system works. I am going to look into an oil catch can, even though my car is not supercharged; it is, however getting older and obviously with increasingly higher mileage, so anything I do to potentially reduce oil in the intake must surely be to the good?
I am also looking into whether I am burning Transmission Fluid? I understand that it burns with an acrid rubber burning smell like mine and there is an ongoing link between a transmission fault (P0783), a Gearbox Fault light (comes on, goes off again) and the cloud of grey smoke that literally pours out of my exhaust/exhausts from time to time. Often, a gear 'slip' precedes a strong smell of burning rubber which we notice BEFORE (i.e. probably from under the bonnet) we see a great cloud of grey smoke out of the back....
Regards,
Ray

 

You may be on to something here Ray.

The clunk and then the smoke and the P0783.

I doubt the transmission fluid gets "in to" the exhaust however it certainly could get on to the hot exhaust and cause smoke and a burning smell.

Anyway you can look around the transmission to see if there are any leaks?

Also next time this happens any way to stop quickly, safely, and see if smoke wafts up around the car and not from the rear?

 

I have had the 'clouds of grey/white smoke' in the past and I think it was due to

oil settling in the corrugated pipe between the engine and the PCV.

I believe it occurs on cars that are driven around town a lot and not many long runs.

I suggest that you find a stretch of quiet,straight road and kick her down couple of times,

that's what I did anyway.

 

Try to forgive me, but I still cannot get my head fully round this PCV Valve!
My understanding is that it is closed at idle because high inlet manifold vacuum at idle overcomes the spring and closes the valve? If this is so, when you remove the valve from the Cam Cover, why is there a vacuum at the Cam Cover pipe on idle with the valve closed? Surly the opposite should be true - No vacuum at Cam Cover on idle?

 

I second what jackra_1 said, there's no way trans fluid is getting into the exhaust. Maybe you have a ruptured cooler line blowing oil onto the cat converter? I'd check this asap, you don't want to start a fire under the car.

Re: the PCV--the unit on this engine doesn't close at idle. It is a flow control only, so manifold vacuum (or close to it) will be applied to the crankcase at idle. From what I can tell, the valve is a flow regulator, not a pressure regulator like the old PCV valves.

 

I had an old Rambler that had a bad modulator valve that was sticking. Therefore sucking transmission fluid into the combustion chamber, sending a huge cloud of smoke out the tail pipe. Looking almost like a James Bond escape trick, everyone backed off from the cloud. Was kinda funny to me but the wife was not amused at all. Changed the valve and it all went away.

 

Thanks Mike. I am happy to be able to tell you that the smoke is most definitely coming out of the exhausts! As to what this valve does, that's anyone's guess; you can blow through it from both directions and nothing happens. You can suck it in both directions and nothing happens. The only time it does anything is if you block-off one end or the other, in which case the diaphragm acts. Problem for me is, who is available in my inlet manifold or in my Crankcase to stick their finger over either of these two pipes?

In a simple world, you could visualise a valve that opens when the crankcase pressure gets too high, bearing in mind the valve is supposed to be relieving blow-by crankcase pressure without increasing emissions, and even then, some sort of filter would be indicated if you believe that clouds of oily smoke are just as undesirable as the blow-by products you are trying to eliminate?
I can visualise a Cam Cover mounted Crankcase valve which released excessive Crankcase pressure, and then utilises an inlet vacuum to pull the excess gases through a good, strong filter - That would appear to me to be a very good idea!

However, I cannot visualise how this PCV achieves anything (obviously that does not mean that it does not achieve anything, only that I cannot visualise it)!

 

Wingrider, thanks for your post, but I have been clearly instructed that our Jaguars have an entirely electronic gearbox and accordingly we do not have a vacuum-based modulator valve. However, thank you for reminding me of an old buddy of mine who had a Rambler Rebel a million years ago, with a Nitro feeder fitted'; such fun to see this huge 'Yank Tank' (sorry) leave so many go faster cars of that time standing at the lights!
Regards,
Ray

 

'From what I can tell, the valve is a flow regulator, not a pressure regulator like the old PCV valves'.

Michael, did your new PCV make any difference, please?
Regards,
Ray

 

No, the new valve and old valve work exactly the same. There was nothing wrong with the old one.

 

Sir Michael, Thank you again.
I am fitting an Oil Catch Can, because if my problem is not the PCV Valve, then it may well be excessive blow-by (although my engine appears to pull fine and does not smoke until it does so on the odd occasions and with a massive smoke 'event') and therefore the extra 'filter' can only help?
Regards,
Ray

 

Can't hurt. I need to get to that issue on my cars, all of them.