Quick pcv valve question

[Got Boost?]

I'm doing my injectors so I thought it would be a good time to check the pcv valve(original). funny thing is that it says ac delco spark plug type cv 770 c on it? Is that correct?

And it should stop all air from going into it from the top right? I unhooked it where the hard line meets rubber and when I blow through it, you can hear alittle air come out, good or bad?

Thanks guys

 

[Got Boost?]

Oh yeah, just checked gnttype and they say the part number is ac cv893 c? So which one is everyone useing?

 

[bose]

pcv valve

Don't forget you can't blow through it as hard as the boost will push against it.With the extra pressure of the boost it should seal.Whatever you do don't use one of those check valves thatr some of the vendors sell.a guy at the track where I run was using one and he had numerous problems until he took it out.Bruce

 

[TurboDave]

893 is the correct part number. The 770 is for normally aspirated engines and will be metering an incorrect amount of ventilation.

It is normal for some air to leak past in the "wrong" direction, the important feature is the amount of vacuum that is allowed past it. This is very important in the overall scheme of MAF calibration and this PCV air is accounted for in the MAF calibration. The wrong PCV will skew the MAF numbers in the wrong direction, especially at idle.

Using only a check valve in place of the PCV will really drive the MAF idle number whacky.

 

[Roger]

Originally posted by TurboDave
893 is the correct part number. The 770 is for normally aspirated engines and will be metering an incorrect amount of ventilation.

It is normal for some air to leak past in the "wrong" direction, the important feature is the amount of vacuum that is allowed past it. This is very important in the overall scheme of MAF calibration and this PCV air is accounted for in the MAF calibration. The wrong PCV will skew the MAF numbers in the wrong direction, especially at idle.

Using only a check valve in place of the PCV will really drive the MAF idle number whacky.

Dave I just acquired an ATR PCV valve which has a positive shutoff. I have a buddy w/ the Kirban check valve & no problems.
Are yo saying that a positive shutoff is detrimental.
TIA

 

[darkfa8]

good or bad?

I have the in-line check valve from Poston's. I thought it was supposed to prevent boost pressure from entering the crankcase and causing trouble with seals?

I have breathers on both valve covers...so is having this aftermarket check valve detrimental to the operation of the pcv valve under normal vacuum and/or under boost pressures?

If the pcv is good, a sc delco unit...it is supposed to seal under boost? If that's the case, using a in-line check valve is redundant and/or cause for complications? Is this logic correct?

I'm suffering from high BLMs and I can't find any other vacuum leaks...so far as I know

 

[8UWITH6]

I have a few questions too.....on my GN I have the breather bypasses and a check valve of an unknown brand. Its brass and takes place of the PCV, its not the ATR valve. It seems to work well??

But on my ttype, I have breather bypass and just a Delco PCV valve, no check valve. Is this bad? I get some oil out of the vac pod sometimes, and obviously around the PCV valve itself. Occasionally Ill pull the vac pod off and clean the oil out of it/off it. Whats up with this?? Is it from boost getting into the crankcase?? Im not too framiliar with the PCV system, but I know the basics. If you can help, email me or post here, thanks.

 

[Buick Mark]

I have both valve cover breathers and WAS running the correct pcv valve, but I got tired of the oil getting sucked in the throttle body. I plugged the hose with a valve stem cap, and my idle improved, and so did my drivability. I believe with the breathers in the valve covers AND the pcv valve that it basically opens the crankcase to the atmosphere resulting in too much vacuum being drawn thru the pcv system, the pcv is suppose to operate with a closed crankcase, the only outside air being drawn into the engine is from the right valve cover hose that attaches after the maf. So I would think, yes, the maf would compensate with the factory setup, but when we add the breathers AND keep the pcv, we basicaly end up with a huge vacuum leak. 'Course I could be wrong too. Mark

 

[TurboDave]

Even with the breathers, running the "correct" PCV and keeping it changed once a year will not be detrimental, nor will it result in "too much" vacuum being sucked in.

The PCV (the right one that is, and in good condition) is what the system is metered for, and the MAF is calibrated to account for that vacuum bypassing it.
You put in a check valve in place of the PCV, and you now have a massive vacuum leak that the MAF isn't calibrated to account for. Generally leads to very lean idle conditions.
Plug the PCV system up and this yields a very rich idle condition (which is why it "seems" to run better). Of course it seems to run better, that's why open loop idle chips give the impression of nice smooth idle characteristics. The richer the idle, the smoother. Assuming the computer is no longer able to correct for it (BLM's at their stops).
Sorry Mark, but if you're theory held any water, niether of my GN's would be running correctly. Nor any of the others I've tuned. Sorry, it just takes the right parts, and no, a PCV will not last forever. I replace them no less than once a year.


Just because an AC or Delco PCV has been used doen't mean it's the correct one. Go into any parts house and ask for a PCV, and I'll bet you dollors to donuts they'll try and sell you the wrong one. (non 893)

 

[GNVAIR]

I have a check valve that I bought from Modern Muscle that goes inline and is used with the PCV. Do you think this is detrimental?

 

[GSX-PKV]

I claim to be no expert, but I have had a PCV check valve in my car for several years with no downsides. I have the ATR version. I have 2 breathers. I always noticed an oil residue in my upper plenum prior to installing a check valve about 8-10 years ago. It might just be good luck, but my car has always idled as smooth as silk and it runs great 1/4 mile times and MPH.

An idea for anyone concerned would be to use the check valve at the track where you have very high boost, and when driving on the street, switch to a stock part# PCV valve... it would only take 5 seconds to accomplish that.

 

[tom h]

Since the MAF is calibrated to take account of the air entering the intake thru the PCV valve, it seems that even if the PCV valve was unplugged from the crankcase and simply allowed to "inhale" underhood air, then all calibrations would remain intact (plug the open PCV hole in the "valley"!)

Of course, the crankcase would need breathers to relieve blow-by, but it seems most of us use valve cover breathers, anyway.

So why would anyone want to let the PCV valve dangle and let it breathe "freely"? It seems that less oil vapors might be sucked into the intake -- less gunk to cause deposits, pinging, etc.
(same reason most people disconnect the Turbo intake from the valve cover, for example).

Is this reasoning sound, or am I missing something?

Any of you running with the PCV valve breathing "underhood air", instead of the crankcase?

 

[TurboKen]

Some of the fast guys out here put 2 pcv valves inline to stop the oil from entering the tb under boost. This may be strictly for race use only, I don't know. Do you think this setup works? Ken

 

[tom h]

Under boost, the throttle body is under high positive pressure (20-25 psi), so maybe the 2 PCV valves is for better insurance against presurizing the crankcase and forcing oil vapors out the valve cover breathers. But under boost, the pressure difference is the wrong direction to suck oil into the Throttle Body.


The PCV valve allows suction from crankcase into Throttle Body only under high manifold vacuum conditions, i.e. idle or constant speed cruise under light load.

 

[gnturbo]

Well I actually found a brass pcv valve at napa that fits the vacuum line between the pcv and the hard steel line.if the vacuum gets too hig it will close off and not let gases into the tb.Under boost it lets the stocker do its thing.What are some things to look for if it is restricting gas flow or not allowing enough air flow through the crankcase?

 

[Ormand]

Stock flow, through the MAF

On a stock '86 or '87 Turb0 Buick, right from the showroom, the only path for air into the crankcase is the breather on the drivers side valve cover, which connects to the turbo inlet. The ONLY air that can get to the crankcase has already been measured by the MAF. When the intake manifold is under vacuum, then the air from the turbo inlet is sucked through the crankcase, purging vapors, and on into the manifold throught the PCV valve. The MAF measures this air flow, and the fuel injected is "calibrated" to include it. HOWEVER- as soon as the engine gets warm, the stock chip goes into closed loop, so the O2 sensor is controlling mixture. Under boost, the only path out is still the breather at the turbo inlet, so all the crankcase vapors now go out through the turbo. If the PCV leaks back a little, it won't be much, and it "should" go out through the stock breather. One problem with this is the location of the stock breather, which will allow oil to be carried over into the turbo. Not good! When new breathers are added, and the chip is changed to one that doesn't use closed loop at idle, most of the above does not apply. But the stock breather location is still bad.