ok its a big one but how exactly does the pcv system work, the valves allow gasses through when theres vacuum in the intake , when the intake is pressurized the valve is closed so your bottom end of the engine isnt pressurized and the dipstick doesn't pop out, i cant see how these valves sticking open or closed would make the car smoke on idle as thats what the valves are supposed to bloody do isnt it ( let the crank gasses into the intake ), so what is the real cause of smoke on idle?

The key to understanding why a worn / weak and leaking valve can be the cause of smoke at idle is to understand in more detail what happens in a fully functioning valve.

 

The valves do work how you mentioned well sort of..... they do close when on boost as the boost pressure acts against the free side of the valve and shuts them.

 

However when on idle the valve is opened but not fully, remember there is a closing spring fitted albeit a weak one acting against the vacuum BUT more importantly the amount of vacuum acting on the valve is reduced by the restrictor fitted in the rubber pipe.

 

The sump air itself is also restricted by the very nature of its design so there is an on going balancing act at tick over where the valve is opened slightly but enough to draw oil laden air into the intake, now a valve with a broken or weak spring will open fully and so cannot maintain that important air balance and as a consequence will draw oil laden air into the combustion chamber and hence smoke at idle.

 

An interesting point, we know the all important restrictor in the rubber pipe directly effects the amount of valve opening and hence emissions, US sourced pcv rubber pipes have different sized restrictors in than UK sourced ones, most likely an emissions thing, this would also point to why some cars have problems at MOT time with the emissions, which in part could be caused by faulty valves or rubber pipes with no restrictors in ( Non Nissan )

 

Robertz

cheers fella

Edit to above missed a word out *............Doh!!

 

The sump air itself is also restricted by the very nature of its design so there is an on going balancing act at tick over where the valve is opened slightly but *NOT enough to draw oil laden air into the intake, now a valve with a broken or weak spring will open fully and so cannot maintain that important air balance and as a consequence will draw oil laden air into the combustion chamber and hence smoke at idle.

 

Robertz

Should the restrictor be in the drivers side PCV pipe or passenger one? mine smokes on idle too. I originally thought the restirctor was in both sides, but hve been told since that its only the drivers side. Also which side does the metal brush filter go into? Im told that is as equally important as the restrictor as it seperate the oil from the air.

 

 

The reason i cant confirm either is that i dont have a drivers side pcv pipe, i also dont have the solid metal pipe going round the rear of the plenum... as details in my wanted ad:

 

More for Jeffs Attention really:

http://www.300zx.co.uk/forums/showthread.php?t=120535

Hi John,

 

AS far as the hard pipe at the rear of the engine is concerned then can supply you that from stock no worries, the restrictors you mention are an essential part of the pcv / pipe system and its balance, so much so that if you purchase the pipes from the US and depending which state the Nissan dealer is located the restricter size is different, which no doubt has some bearing on the different emmission laws between states and between the US and UK. The metal brush is designes as a flame trap and is fittedin the front pipes to the inner camcovers

 

 

It is for that reason a word of caution is required when purchasing certain parts from the US dealer network, this is my view and I know some traders who have in the past purchased these and other parts will most likely disagree, but I deal in real world mechanics everyday not just behind a pc screen and Sunday afternoon tinkering.

 

 

PM me have you address and can post your bits out FOC of course.

 

 

 

 

Oh and HAPPY NEW YEAR to all on the forum

 

 

Jeff TT

Edited January 1, 200917 yr by JeffTT

I have emailed you last week regarding a few issues im having, not sure you got it, possibly spam filter? no reply yet :)

 

Cant PM (yet).

 

my email address: is johnobrien1978@hotmail.com if you can email me on there i'd appreciate it lots.

 

What is FOC?

 

Cheers Jeff

I have emailed you last week regarding a few issues im having, not sure you got it, possibly spam filter? no reply yet :)

 

Cant PM (yet).

 

my email address: is johnobrien1978@hotmail.com if you can email me on there i'd appreciate it lots.

 

What is FOC?

 

Cheers Jeff

 

 

 

Ah ha most likely e-mailed me at work, will mail you in a sec so you have my home addy, oh and FOC = FREE OF CHARGE:D

 

Jeff TT

What is FOC?

 

Free Of Charge :D

haha, free postage?

 

excuse my confusion here.. lol

haha, free postage?

 

excuse my confusion here.. lol

 

 

No! totally free, they are spare parts we have loads of so if it helps you out thats fine by me, ask others here its just my way.

 

 

Jeff TT