PCV system questions

[suprafanatic]

Yesterday I did a boost leak test. I found that my PCV system was blowing air pressure straight out back into the intake hose. It was coming out of the port on the throttle body that goes to the top of the valve covers and then to the intake hose. I was under the impression that the PCV system should only be seeing vacuum. Should boost be coming out there? If not what should I do to fix it? Thanks.

 

[jetjock]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=EC&P=5

 

[suprafanatic]

In looking at that it doesn't really answer what im looking for. That picture is to small for me to tell which way some of the arrows are pointing. I'm assuming boost is not suppose to be coming out of the throttle body port for the PCV system. That would pressurize the crankcase rather than pull the pressure out. Alot of people have said to just cap the line between the throttle port and valve covers. But will this cause any problems? What about putting a check valve inline between the two?

 

[jetjock]

Look at the rest of the page. Or save the photo and enlarge it.

Pressurize the crankcase? Are you serious? And you were arguing electrical stuff with an EE?

 

[Turbo Habanero]

I'm not really sure how the PCV system works but i've heard it can cause all sorts of problems even smoking in some cases.

Although i would not recommend capping them off

 

[suprafanatic]

Well the crankcase pressure is suppose to come up out of the valve cover ports correct? but if theres boost pressure going through those lines and into the valve covers its going to keep the crankcase pressure inside won't it? When it comes to the PCV system I'll be honest I don't know much. Or at least I thought I did, but I guess I'm wrong.

 

[CyFi6]

I think you are disregarding the hose going down the the accordion.

 

[jetjock]

^ That.

OP: The system flows both ways. Below atmospheric pressure fresh air for dilution is drawn from the accordion to be mixed with HC from the valve covers before going into the TB to be combusted. Above atmospheric pressure air is metered out of the TB through an orifice to pick up HC on it's way to the accordion to again be burned in the engine.

In both directions flow at right angles to the valve covers helps with scavenging. Think blowing across the top of a bottle. It's only under high levels of boost that the accordion inlet is at lower pressure than atmospheric and even then not by much. Finally, before screwing with the PCV system, you may want to consider under which condition the engine spends the vast majority of it's time.

 

[suprafanatic]

I was not disregarding the accordion hose. However, I was thinking it was pointless for boost to be blowing back into the accordion hose. Just like when my BOV was bad. It was simply blowing boost back into the accordion hose. So to me it seemed like a rather large boost leak.

BUT, I have to thank your for explaining how it works to me! Yes the TSRM can be helpful, but it does not give me details that I need like what you just gave me. So again, thank your for taking your time to explain it to me. That's all I really needed.

 

[AJ'S 88NA]

Don't think a lot of guys just cap the PVC off, you'd have a lot of pressure pushing oil out the seals.

 

[suprafanatic]

I'm only talking one end capped off. The accordion hose would still be sucking pressure out. But the way JetJock described it, it makes more sense to me. To me though it still seem like it would be a sort of boost leak. Yes its staying within the metered air system, but that's alot of air pressure going back into the air intake rather than going into the cylinders. When we did the boost leak test we couldn't even build up any pressure in the system to look for leaks because all the air was coming straight out of the PCV system. I would imagen the turbo would have to work extremely hard to be able to produce any kind of pressure with that situation. I feel like my whole thought process of how all this works is flawed. And mostly likely because it is. I just have this idea that everything should be sealed and all the boost pressure should be going into the cylinders, and the cylinders only.

 

[CyFi6]

Though I have never personally done a boost leak test and seen how much air really comes out that restriction in the throttle body, compare the CFM of your air compressor/hose to the CFM of your turbo and it might not seem as crazy.

 

[jetjock]

What he said. It's not about pressure. I noticed much of what you think is flawed. Ever hear of the Dunning-Kruger effect? Maybe you should just leave things alone until know at least as much as the engineers who designed the car.

 

[IBoughtASupra]

This guy Jetjock seems to act like he knows everything or maybe......

OP, 7M don't have true check valves, just an orfice. It wont be an actual boost leak because its not a huge hole. Keep in mind, it works perfectly fine.

When I had my 7M, I have the PCV hooked up AND it was done like stock and worked flawlessly.

I believe it was Ian who posted that the 7M doesn't have a true check valve as well, but don't quote me on that.

 

[suprafanatic]

lol, might not be a big hole but there was A LOT of air coming out of it. Either way, if that's how its suppose to work then that's fine. I will leave it how it is! I did however put all new clamps on the PCV hoses. The stock ones were to loose and actually causing a leak into the open air, so I was losing some metered air from that. Now if I were to add an Oil catch can into the PCV system would it go between the accordion hose and the valve covers?

 

[IJ.]

This guy Jetjock seems to act like he knows everything or maybe......

OP, 7M don't have true check valves, just an orfice. It wont be an actual boost leak because its not a huge hole. Keep in mind, it works perfectly fine.

When I had my 7M, I have the PCV hooked up AND it was done like stock and worked flawlessly.

I believe it was Ian who posted that the 7M doesn't have a true check valve as well, but don't quote me on that.

And it was JJ that educated me on how the 7M system works, people should listen when he posts!

 

[IBoughtASupra]

And it was JJ that educated me on how the 7M system works, people should listen when he posts!

Darn right. I sure do.

 

[ATL88Supra]

i got tired of dealing with mine so i just moved it to my down pipe so its always under vac

i welded up that stupid throttle body boost leak

it may not be the right way but it sure is better that that shitty system it has stock

 

[Poodles]

i got tired of dealing with mine so i just moved it to my down pipe so its always under vac

i welded up that stupid throttle body boost leak

it may not be the right way but it sure is better that that shitty system it has stock

- Will destroy a catalytic converter.
- Illegal for emissions.
- Only works during high flow.
- Doesn't work the rest of the time.

In other words, it's good for a drag car since it's full throttle use (and emissions don't matter) but all but worthless anywhere else.

 

[Nick M]

That would pressurize the crankcase rather than pull the pressure out.

The system pulls the combustion by product out so sludge and other nasty things don't happen. It (PCV) has nothing to do with pressure.