what are the symtoms of a bad pvc

N

newhotair

Member
Joined
Oct 17, 2010
I need to know the symptoms of a bad pvc valve and also what would a bad egr make the car act like
 
Both stuck open would cause a stumbling idle. Closed on either would do relatively nothing.

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A closed PVC would cause oil leaks. It would create excessive crankcase pressure and split/crack gaskets.


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A stuck closed EGR would not generally cause problems unless your having en emmision test which you would fail for High NOx. If an EGR is open the car would have a bad idle and or stumble and stall


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What's better stock pcv or rjc? My car started leaking oil and I have the rjc pcv

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The stock PVC is a calibrated air leak. The ECM expects a given amount of air at Idle and cruse on top of what the MAF reads. If your PCV leaks more than it should, the engine will have more air than the fuel tables expect. If it's slight the ECM can use feedback from the 02 to correct it. If it's extreme the computer cant correct it and you'll notice BLMs and INTs maxed out, or worse. If it really sucks air it can gather up oil mist and cause smokeing, ESP during a throttle chop when vacuum goes through the roof.
Under boost the PCV is forced to act as a check valve to keep boost out of the crank case (and keep from losing the boost in the first place). It's not really designed for that job, but the factory GM units seems to live with it under most cases and boost levels. With extreme boost levels or piece of mind a one way check valve with 0 cracking pressure can take the boost load off the PCV without messing with the fueling.

On the EGR it's job is to send exhaust gases into the intake stream. It has to be closed at idle and WOT for driveability and performance reasons. If the pintle doesn't seal, pressurized exhaust will engine up in the intake at idle. During that time the engine doesn't require much fresh air so a large gulp of exhaust will make it run like crap. The test is to sick your finger under the 'UFO' and lift up on the diaphragm at idle. It that makes it idle like crap, it was working right. A vacuum leak where it mounts will let in unmetered air and cause a running condition too. Much like a malfunctioning PCV.
 
Earl: With the check valve/pcv combination, do you put the pcv in the grommet (stock location) and then install the check on top of that, or the other way around?
 
yes, you put a GM PVC in the hole like normal. Then cut the hose to make room for a check valve. The trick with the check valve is that it has to be rated for the amount of pressure you're going to put to it (so it doesn't blow apart) and most importantly, it has to have a near 0 cracking pressure. What that means is that it needs to open at any vacuum level, and it has to be as invisible as possible to the airstream. That way the PCV gets protected yet the fueling won't get all messed up.
 
earlbrown said:
yes, you put a GM PVC in the hole like normal. Then cut the hose to make room for a check valve. The trick with the check valve is that it has to be rated for the amount of pressure you're going to put to it (so it doesn't blow apart) and most importantly, it has to have a near 0 cracking pressure. What that means is that it needs to open at any vacuum level, and it has to be as invisible as possible to the airstream. That way the PCV gets protected yet the fueling won't get all messed up.
Click to expand...

Thanks Earl!
 
I thought that the pvc only work with vacuum applied? Would that make it a one way check valve already?

If you check the EGR by just pushing up on the "UFO" wouldn't you just check to see if the egr port is clogged with carbon and not checking to see if the diaphragm is torn or has a leak? I usually check it with a vacuum pump to check the integrity of the EGR diaphragm


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If you're clogged with carbon (which is common on the EGR tower, pushing up on the UFO will have no change. With an aftermarket chip that disables EGR it won't really matter. With an EGR chip you might end up with part throttle knock from too much timing and no cylinder dilution.

Yes, the PCV is kind of a check valve already. Its just not designed to be.... and we make it tougher on it by running more than 12 pounds of boost.
 
So with it disabled you can remove the piece on the intake and install block off plate correct?

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Yes. Sometimes those block off plates can leak. Somewhere on here, you can see how some have threaded the holes and screwed pipe plugs in there to seal the openings. Probably would want to remove the intake to do the threading, so as not to get metal chips into the engine.
 
Correct, if the EGR is disabled in the chip you can remove all that stuff and clean up the intake.

Jay, that was me that put in the pipe plugs instead of using a plate. The intake really needs to be off and on a milling machine. The top hole is rectangular and BARELY small enough to make he pipe plug fit tightly. It's worth it in the end though. That setup will NEVER leak no matter how much boost and heat cycles I put to it.
 
earlbrown said:
If you're clogged with carbon (which is common on the EGR tower, pushing up on the UFO will have no change. With an aftermarket chip that disables EGR it won't really matter. With an EGR chip you might end up with part throttle knock from too much timing and no cylinder dilution.

Yes, the PCV is kind of a check valve already. Its just not designed to be.... and we make it tougher on it by running more than 12 pounds of boost.
Click to expand...

RE: - The PCV
I've found no matter the brand - no matter if they are brand new out of the box - they all leak even at the stock levels of boost - let alone the +20 PSI alot of people run.
They are a major source of crankcase pressure and boost leak.
And with that 3/8" I.D - they can blow alot of air.
I check them with my adjustable air regulator set to 18 psi and they still blow like crazy

I use these 3/8" in line with my PCV:
http://www.usplastic.com/catalog/item.aspx?itemid=36844

X2 on Earl's recommendation of a very low crack pressure.
That is a key
 

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