pcv

85 Coupe 5.0 · Jan 28, 2004

one more passage, here we actually measure the airflow of the PCV valve. Why is this improtant? because if the PCV is flowing too much, it will cause a lean condition at idle and part throttle, again, because the PCV airflow is NOT measured by the VAM/Mass Air Meter

Notice how they even want to setup the test on the engine size this is because a larger engine would require more airflow through the PCV system to properly remove crankcase vapors.

Stinger · Jan 28, 2004

Well, it all sounds good in theory and the "proof" is in your book there...I've just never seen the size of the PCV have any effect on a 2.3T engine. I've seen so many different ways to set up the PCV system it's not even funny...that all run the same.

Stinger

85 Coupe 5.0 · Jan 28, 2004

Stinger said:
Well, it all sounds good in theory and the "proof" is in your book there...I've just never seen the size of the PCV have any effect on a 2.3T engine. I've seen so many different ways to set up the PCV system it's not even funny...that all run the same.

Stinger

And you probably are correct, i'm not 100% sure on how the pcv system is setup on the 2.3L turbo motors, But, it is a major part overlooked by most people that wouldn't know the wiser when trying to diagnose a driveability problem. Most of what i have showed you guys applies to stock setups tho, if the computer has been altered it usually will accomodate a change in the pcv system, and stock systems have some degree of tolerance.

Now you know that there is a difference, one pcv is not equal to another and the exact replacement should be used. This especially applies to any vehice '96 and newer when OBDII started getting used. OBDII monitors the powertrain, any change will be picked up. With the tougher emission standards nowdays, an improper PCV valve will be detected due to the improper airflow, the computer correcting by altering the fuel trim, and a trouble code set.

blastit116 · Jan 28, 2004

come to think about is tere was a sound that sounded like a leak but i lookedaround pretty good a could not find it i will look agian this weekend

blastit116 · Jan 28, 2004

come to think about is tere was a sound that sounded like a leak but i lookedaround pretty good a could not find it i will look agian this weekend

85 Coupe 5.0 · Jan 28, 2004

Here are some passages from my Computer Controls Book. This book does an EXTREMELY good job of describing the PCV system. Notice how it says the air/fuel mixture will be lean if the PCV is incorrect, again, because the air being drawn through the PCV system isn't measured.

jjxusaf · Jan 29, 2004

Hey there...doing some PCV research myself so I thought I'd chime in. Not trying to start an argument or anything, just trying to understand it all. That being said...

My understanding of PCV systems was that there were two types, open and closed. My car (95 GT) uses the closed type so I'll focus on that. I was under the impression that air passes through the air filter, through the MAF (or other applicable air meter), and then, before the throttle body, there is a line connected to the valve cover (or oil fill tube). The purpose of this line is to let fresh air into the crankcase, and this fresh air is then sucked out through the PCV valve, and released into the intake. Since it is a 'closed' system, all of the air in the engine has passed through the MAF, and is thereby accounted for.

The flaw in your reasoning that I see is that you don't explain where the air in the crankcase comes from. Sure, some of it comes from blowby, and you could say that air is not metered because once it passes through the combustion chamber the computer considers it gone, but if your engine is experiencing that much blowby then you've got some serious ring issues.

I've always read that the purpose of the PCV system way two fold. At idle, when there is little to no blowby, the tube connected to the intake before the throttle body lets fresh, metered, filtered air into the crankcase and the PCV valve sucks the nasty oily air out of the crankcase. At higher RPMs when there could be blowby, the pressure created can escape through either the PCV valve or the line on the valve cover.

Please correct me if I'm wrong, as I'm still learning. I don't need any proof from a book, I'm just trying to understand.

Oh and by the way an open PCV system would be one where the incoming air is not metered, like a carb setup. In this case it's perfectly fine to run an open breather on the oil fill/valve cover.

Stinger · Jan 30, 2004

I agree

Brantley · Jan 30, 2004

Wish I had replied here sooner, but I have been really busy with work and school.

I think I mostly agree with 85_coupe, it's just that we are not really talking on the same level. I got really hung up on his claim that the PCV was metered. I just don't see how that's possible. It's a flow restrictor calibrated to match the engine and it's blow-by curve at X RPM. There is no sensor that knows how much air is coming up the PCV tube!

Also, as jjxusaf states, we have the issue of where the air comes from. I have been thinking on this, and on OUR ENGINES I can only see 2 places that air can get into the crankcase (other than blow-by) - the valve cover breather and the PCV tube. Both of those points are downstream from the VAM, so the air in the crankcase has been metered indirectly, unless I'm missing something.

I plan on putting a new EV-127-A PCV valve back in my line, but I will be leaving my check valve on the line as well. Now I'm kinda interested to see if makes any difference or not.

This is the article that I found on the PCV thing that made the most sense to me. Especially the last 2 to 3 pages are very good.

a351Must2 · Jan 30, 2004

I wish I'd caught this thread earlier...just to say exactly what I quoted here... The PCV system is a closed system and therefore the air through the PCV is metered. '85 Coupe's books mention plenty that is dead on accurate, he's just not translating it all right in his head. I did learn one thing from what he showed though...the EEC computer expects ~20% of the air at idle to come through the PCV valve, thus "in theory", replacing the PCV valve with a pipe and allowing full intake vacuum flow through the crankcase would allow more air to bypass the throttle body than the computer expects and would act like the IAC is stuck open.

jjxusaf said:
Hey there...doing some PCV research myself so I thought I'd chime in. Not trying to start an argument or anything, just trying to understand it all. That being said...

My understanding of PCV systems was that there were two types, open and closed. My car (95 GT) uses the closed type so I'll focus on that. I was under the impression that air passes through the air filter, through the MAF (or other applicable air meter), and then, before the throttle body, there is a line connected to the valve cover (or oil fill tube). The purpose of this line is to let fresh air into the crankcase, and this fresh air is then sucked out through the PCV valve, and released into the intake. Since it is a 'closed' system, all of the air in the engine has passed through the MAF, and is thereby accounted for.

The flaw in your reasoning that I see is that you don't explain where the air in the crankcase comes from. Sure, some of it comes from blowby, and you could say that air is not metered because once it passes through the combustion chamber the computer considers it gone, but if your engine is experiencing that much blowby then you've got some serious ring issues.

I've always read that the purpose of the PCV system way two fold. At idle, when there is little to no blowby, the tube connected to the intake before the throttle body lets fresh, metered, filtered air into the crankcase and the PCV valve sucks the nasty oily air out of the crankcase. At higher RPMs when there could be blowby, the pressure created can escape through either the PCV valve or the line on the valve cover.

Please correct me if I'm wrong, as I'm still learning. I don't need any proof from a book, I'm just trying to understand.

Oh and by the way an open PCV system would be one where the incoming air is not metered, like a carb setup. In this case it's perfectly fine to run an open breather on the oil fill/valve cover.

85 Coupe 5.0 · Jan 30, 2004

a351Must2 said:
I wish I'd caught this thread earlier...just to say exactly what I quoted here... The PCV system is a closed system and therefore the air through the PCV is metered. '85 Coupe's books mention plenty that is dead on accurate, he's just not translating it all right in his head. I did learn one thing from what he showed though...the EEC computer expects ~20% of the air at idle to come through the PCV valve, thus "in theory", removing the PCV valve and allowing full intake vacuum flow through the crankcase would allow more air to bypass the throttle body and would act like the IAC is stuck open.

That is EXACTLY what I was trying to get at. The ECU expects a certain amount of air through the PCV system. Altering this system will create a problem.

As for the metered air issue, I was thinking a carb setup, where the air is taken from the air cleaner itself. Air for the fuel injected motors, the PCV air is taken after the VAM/Mass Air, so it is thereby measured. So my hats off to the two people who chimed in on that, thanks for correcting.

BUT

Like stated above, the ECU (computer) expects 20% of the idle airflow it requires from the PCV. So to re-cap, if you have the incorrect/backyard PCV valve on your car, it will effect the idle quality and certain other factors. This is probalby why some of you guys are experiencing idle speeds of 1500 to 1800 RPM, surging idle, ect. Incorrect PCV valve.

Brantley · Jan 30, 2004

That the ECU expects a certain amount of air is what I had concluded.. that's why I had a problem with saying it was "metered."

I don't have any experience with carb'd engines, so my 2.3 and 4.0 Ford engines are the only ones that I have done much with.

From the first day I fired up my rebuilt engine, it has always idled high. I have tried some stuff, and I have list of other stuff to check. PCV is probably part of it, but I know there's more to it than that. I suppose that's why I really didn't see any significant change when I put in my check valve.

85 Coupe 5.0 · Jan 30, 2004

Technically it is metered.

The ECU expects 20% of the air it needs for idle to flow through the PCV valve.

So say we've got a 2.3 - 140, it uses 3 grams air/sec at idle, so it's going to expect .06 grams of air from the PCV valve. (these aren't specific numbers.)

Ok, now let's say we have a 460. it consumes 6 grams of air/sec at idle. This setup will require 0.12 Grams of air from that PCV valve.

So you couldn't interchange the PCV vavles from those two examples, even if they look the same, one will allow more airflow through it.

Get the point? PCV valves are metered and are specific to the combination they are in.

I was wrong about the air not being measured by the VAM/Mass Air meter. and I admit I was on that. I was interperting it wrong, congrats Stinger and the others who pointed it out.

BUT, the PCV vavle is specific, it is metered and does make a difference which one you get, i think that's why this all started anyhow?

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