pcv

The fact that it was unplugged could be the problem...that creates a massive vacuum leak.

Stinger

If you changed plug wires, you might have dislocated the pcv valve, and like Stinger sais, created a nice vacuum leak. I had a similar problem, the pcv valve just broke in 2
Don't know how or why it did that, but that thing kept me awake for several nights.
Engine had the same problems as you describe, and absolutely no power. I wasn't able to drive it out the garage.
A new one isn't expensive, might be worth it

Hey, a PCV question. I checked mine the other day and it was in pretty bad shape, so I went up to the auto parts store and all they sell are these stupid Purolator things that are bent into a 90 degree angle and have that little cap off section on them and I told the guy "That looks nothing like mine" and he was like "Oh, they do that now so it will fit onto more than just one vehicle now, for "convenience."" Yeah, "convenience" my cornhole. I buy it, go out to hook it up, and the hoses don't fit up right which creates a great little vacuum leak if left connected. So, I pull it out and toss it, 3 bucks gone since its now "used" and clean off the old one a bit and throw it back in. The PCV is pretty loose in there now, could definately use a new one. Does anyone have the ORIGINAL Motorcraft Part number and a place I might be able to find it? I tried Autozone, Pep Boys, and Advanced Auto Parts and all they sell are the Purolators.

ah, got to love the parts stores where nobody has absolutely no experience or training.......

O.K.

A P.C.V valve is basically a metered vacuum leak that draws crankcase vapors into the intake and burns them. think about that, a METERED vacuum leak. The computer is calibrated so that it knows how much air will pass through the P.C.V valve. This is VERY important, because the air being passed through the P.C.V. is not measured, because it's after the mass air flow meter. For those of you with speed density it's the same situation, only no mass air meter. P.C.V. valves are calibrated, specific to the vehicle they are in. When you purchase a P.C.V. valve, get an O.E. one. The reasoning behind this is because most of the cheap aftermarket manufactures, ex. FRAM, make one valve for many vehicles. The O.E. valve will be SPECIFICALLY for THAT engine/vehicle combination. Don't let the stupid people at Autozone (sorry to anyone that works there, not all of them are stupid, it's just been my experience that every time i go into one they don't have a f*ing clue) tell you any different. You can get a Motorcraft, Borg-Warner or Niehoff or something similar for VERY cheap.

That is 100% of your prob. Had the problem and it fixed it when i replaced it when it was disconnected.

Wayne

85 Coupe 5.0 said:

ah, got to love the parts stores where nobody has absolutely no experience or training.......

O.K.

A P.C.V valve is basically a metered vacuum leak that draws crankcase vapors into the intake and burns them. think about that, a METERED vacuum leak. The computer is calibrated so that it knows how much air will pass through the P.C.V valve. This is VERY important, because the air being passed through the P.C.V. is not measured, because it's after the mass air flow meter. For those of you with speed density it's the same situation, only no mass air meter. P.C.V. valves are calibrated, specific to the vehicle they are in. When you purchase a P.C.V. valve, get an O.E. one. The reasoning behind this is because most of the cheap aftermarket manufactures, ex. FRAM, make one valve for many vehicles. The O.E. valve will be SPECIFICALLY for THAT engine/vehicle combination. Don't let the stupid people at Autozone (sorry to anyone that works there, not all of them are stupid, it's just been my experience that every time i go into one they don't have a f*ing clue) tell you any different. You can get a Motorcraft, Borg-Warner or Niehoff or something similar for VERY cheap.

Click to expand...

Ok.. now that makes me wonder. On my turbo engine, I put a brand new EV-127A PCV valve on there.. by 3000 miles, it was leaking and I was pressurizing the crankcase under boost. I decided to make my own PCV valve from stuff at Lowe's. After installing my valve, it ran much better and the boost no longer dropped off from the initial pressure. (Held 18psi for a full gear, instead of dropping off 1 or 2 psi.) I know my PCV valve flows more under a vaccum than the stock valve, so if the air is metered, why were the results only positive? My idle did not change at all, however, it has always idled around 1100-1200 (still working on that part).

I don't think the pcv itself is metered. It is part of the metered air system (as in, it went through the air meter at one time) but once it's in the system it doesn't matter what size it is.

Stinger

Don't the part store pcvs have the plastic part that you can take off?
Autozone here always has them in 2 pieces. I wouldn't use it for a turbo app. but...

Stinger said:

I don't think the pcv itself is metered. It is part of the metered air system (as in, it went through the air meter at one time) but once it's in the system it doesn't matter what size it is.

Stinger

Click to expand...

That's how I thought it worked.. I could have just mis-read 85_coupe's post.

Stinger said:

I don't think the pcv itself is metered. It is part of the metered air system (as in, it went through the air meter at one time) but once it's in the system it doesn't matter what size it is.

Stinger

Click to expand...

Stinger, i have to disagree.

If college education didn't say different, i would normally yield to your knowledge.

The air brought in through the P.C.V. system is not measured directly. How can it be? it never passes through the Mass Airflow Sensor. It enters through the P.C.V. valve, which connects to manifold vacuum, which is on the back side of the throttle plate. The computer knows how much air will pass through the P.C.V. valve, and uses this in conjunction with the Throttle Postion Sensor to determine at what percent to open the Idle Air Control Valve Pintle.

Why do you think there are so many P.C.V. valves available? They DO have a specific calibration, how much air is allowed to pass through them.

This is what i see day in day out, some shadetree mechanic puts in a cheap auto parts store P.C.V. valve, it allows too much air to enter through it, the computer tries to compensate, but eventually sets a trouble code. Install O.E. parts, reset trouble codes, test drive, charge customer major $ for simple repair.

I'm not trying to be rude, i'm just making a point, it DOES matter, ask any certified mechanic, or in my case, certified parts specialist.

Brantley said:

Ok.. now that makes me wonder. On my turbo engine, I put a brand new EV-127A PCV valve on there.. by 3000 miles, it was leaking and I was pressurizing the crankcase under boost. I decided to make my own PCV valve from stuff at Lowe's. After installing my valve, it ran much better and the boost no longer dropped off from the initial pressure. (Held 18psi for a full gear, instead of dropping off 1 or 2 psi.) I know my PCV valve flows more under a vaccum than the stock valve, so if the air is metered, why were the results only positive? My idle did not change at all, however, it has always idled around 1100-1200 (still working on that part).

Click to expand...

To be entirely honest with you, i'm really not certain why the results were the way they are in your case. The only thing I can remotely think of in your case is that, on a Naturally Aspirated Setup, the P.C.V. is only open under high manifold vacuum conditions, at idle and cruise. have you ever shook one? hear that rattle? it's a one-way valve. On a Turbocharged setup, the intake manifold is under pressure, in your case, 18 or so P.S.I. So, if you didn't have a one-way check valve in the vacuum line going to your P.C.V. valve, the end of the valve connected to the manifold would have 18 P.S.I. against it, enough to hold the valve shut and cause pressure to build up in the crankcase. On an N/A setup, under wide open throttle conditions the P.C.V. has no pressure against the manifold side of it, and the crankcase pressures that build up can push past the weight of the check valve. In your Turbocharged case, they can't with the 18 P.S.I. of boost against the valve.

This is the only logical theory i can think of.

I have done an '88 TC to '85 Mustang conversion, and i hooked up a one way valve on the P.C.V. and have no problems. The car sees 18 P.S.I of boost daily and has a best of 14.80@94.8 with only an adjustable boost controller.

But again, i'm not extremely familiar with the turbo setups.

I don't know.. I'm still not quite following along here.

The turbo-specific PCV valve, the EV-127A, is a one way valve. As we know, this is supposed to only let air in under vacuum conditions. The valve that I made functions identical to the stock turbo PCV valve. It's a one way valve. Only difference is that mine doesn't distort under the pressure from hose clamps and it can't crack. Should be one less part to fail in the future. What's the difference between a PCV valve with a one-way check valve, or just a one-way check valve that actually works? Are you saying that the stock PCV valve is sort of a flow restrictor of sorts?

I still don't see how it matters about the metering part. The air is still metered by the VAM. The only place that the crankcase should be getting air from is the valve cover breather. In a stock configuration, that breather gets its airflow after the VAM. If it's getting air somewhere else, you have a bad gasket or some screwed rings.

(Hopefully this reply will seem somewhat intelligent. I need to put down the SQL book and go to bed!)

Brantley said:

I don't know.. I'm still not quite following along here.

The turbo-specific PCV valve, the EV-127A, is a one way valve. As we know, this is supposed to only let air in under vacuum conditions. The valve that I made functions identical to the stock turbo PCV valve. It's a one way valve. Only difference is that mine doesn't distort under the pressure from hose clamps and it can't crack. Should be one less part to fail in the future. What's the difference between a PCV valve with a one-way check valve, or just a one-way check valve that actually works? Are you saying that the stock PCV valve is sort of a flow restrictor of sorts?

I still don't see how it matters about the metering part. The air is still metered by the VAM. The only place that the crankcase should be getting air from is the valve cover breather. In a stock configuration, that breather gets its airflow after the VAM. If it's getting air somewhere else, you have a bad gasket or some screwed rings.

(Hopefully this reply will seem somewhat intelligent. I need to put down the SQL book and go to bed!)

Click to expand...

You are correct in one way.

The P.C.V. is basically a flow restrictor.

The air that enters the P.C.V. Valve is NOT metered by the VAM.

How can it be? the air being drawn through the P.C.V. system never passes through the V.A.M. so how can it be measured?

Why do you think it hurts performance so much if you have a huge vacuum leak? Simple. Because the Leak isn't being measured, because it's not being drawn through the VAM, therefore, the computer will not increase the amount of fuel to compensate for the additional air.

A broken or improper P.C.V. valve is basically like a vacuum leak.

The computer is programmed to know how much air will pass through that P.C.V valve at idle, therefore, knows how much fuel to mix with it, or in technical terms, knows how long to make the duty cycle of the injectors. When you build your own or buy the incorrect P.C.V. valve, the amount of air will be more or less than what the computer is programmed, and it can't tell any different because the air entering through the P.C.V system NEVER passes through the VAM, Mass Air, ect. So, the results you see are a high idle, a consistant miss, car won't idle.


Now, back to the Valve thing.

Like i stated before, a stock P.C.V. valve is just that, a valve. On a Naturally Aspirated valve, the pcv allows air to be drawn through it, pulling the plunger up in it as it passes through it. At Wide Open Throttle the manifod vacuum is zero, so the plunger falls shut. As the crankcase pressure builds up it can lift this valve and let the gasses escape very easy, with little or no effort.

Ok, now a turbo setup.

On a Turbo setup, the pcv is connected to a vacuum source just like above. Under idle conditions the pcv is held open by vacuum and crankcase vapors are drawn through it. When at wide open throttle, you guys see relatively 15 or so P.S.I of boost. What is boost? a measure of pressure in the intake manifold. Where is the pcv connected? to the intake manifold.

We are at wide open throttle with 15 psi or so of boost in the manifold. On the n/a setup the pcv plunger would be closed right now, so is the turbo setup. one difference. the 15 psi of pressure in the manifold is pushing down against the plunger inside the pcv vavle, holding it shut. pressure in the crankcase on the opposite side of the valve is starting to build, do to the pressure holding the plunger in the pcv valve being held shut.

I don't know how much clearer I can be.

Although the pressure in the crankcase should be able to escape no problem through the crankcase inlet, it should not build up even on the turbo motor, i really don't know what could cause it, this is just my theory.

BUT I do know the P.C.V. is metered, and if you like, i will photocopy the text out of my school textbook to get my point across.

85 Coupe 5.0 said:

The air brought in through the P.C.V. system is not measured directly. How can it be? it never passes through the Mass Airflow Sensor. It enters through the P.C.V. valve, which connects to manifold vacuum, which is on the back side of the throttle plate. The computer knows how much air will pass through the P.C.V. valve, and uses this in conjunction with the Throttle Postion Sensor to determine at what percent to open the Idle Air Control Valve Pintle.

Click to expand...

Well, I'm no parts specialist but I have a sneeking suspicion that I could put a straigh tube in place of the pcv on my engine and it would run fine under all conditions except boost (when the stock valves closes off of course).

How can it be? it never passes through the Mass Airflow Sensor.

Click to expand...

Are you saying that the PCV air never entered the engine through the airflow meter? I don't agree with that. If you are saying it's not measure when it RE-ENTERS the intake behind the throttle body then I'll agree with that. How is it that a bypass valve (which recirculates air from the TB to after the air meter...like a supersized PCV) works but a blow off (which lets the metered air into the atmosphere) doesn't work?

Stinger

Stinger said:

Well, I'm no parts specialist but I have a sneeking suspicion that I could put a straigh tube in place of the pcv on my engine and it would run fine under all conditions except boost (when the stock valves closes off of course).




Are you saying that the PCV air never entered the engine through the airflow meter? I don't agree with that. If you are saying it's not measure when it RE-ENTERS the intake behind the throttle body then I'll agree with that. How is it that a bypass valve (which recirculates air from the TB to after the air meter...like a supersized PCV) works but a blow off (which lets the metered air into the atmosphere) doesn't work?

Stinger

Click to expand...

Here is a passage from my ASE test prep. book:



I will have a drawing to illustrate how the air entering is not measured, although it states it in the paragraph above.

The words that the date cover up are: a severe effect on idle quality.