Honda Car Forum

On 8 Jun 2004 10:55:51 GMT, "Tegger®"
<teggeratistopdotcom@changetheobvious.invalid> wrote:

>George Macdonald <fammacd=!SPAM^nothanks@tellurian.com> spake unto the
>masses in newsufac0t3919lbv113gr55d8iru2nuv4u7v@4ax.com:
>
>>
>> I know (think ?) we agreed that the PCV is a metered air leak. How
>> can it not affect engine efficiency and therefore fuel mileage?
>
>
>
>Because the air and blowby is coming from, and going to, the SAME PLACE AT
>ALL TIMES.

The valve "orifice" varies considerably according to the relative pressure
of manifold and crankcase

>Go take a good hard look at your own PCV system. See where the crankcase
>takes in air. See where the PCV valve dumps its air. Notice that BOTH are
>located in the INTAKE tract, mere inches from each other?

Go take a *good* look at the path the air, then air+blow-by gas takes in a
Honda system with breather box: air comes in from upstream of the throttle
butterfly through a tube to the valve cover, gets mixed with blow by gas,
sucked into the breather box mounted low on the block and up through the
PCV valve into the manifold. Later models just have the PCV valve mounted
on the valve cover.

>There is NO "air leak".

Yes - it's a metered air leak according to the variable orifice of the PCV.

>The valve does NOT introduce new air into the system.

The air comes from upstream of the throttle - within the operating
parameters of the engine that's atmospheric pressure, minus a little for
the air filter restriction. I dunno what you mean by "new air" but that's
air that the ECU has not measured - it has bypassed the primary device for
signalling mass air flow to the ECU: the throttle and its position sensor.
I'd doubt it has any effect on the IAT or MAP sensors either.

>It simply meters the existing air so as to ensure that there is POSITIVE
>flow through the crankcase, resulting in a constant changeover of the air
>in the crankcase, with any blowby gases routed back through the combustion
>chamber again.
>
>A blocked PCV Valve but a free breather will cause the gases to cavitate
>inside the crankcase. Since the breather will be under slight depression
>from the intake tract, pressure will be higher in the crankcase than the
>intake, so excess gases will get pushed into the intake and recycled
>through the combustion chamber again, just as if they went through the PCV
>properly, but there will be be no positive flow.

The pressure at the air intake end of the breather is highly dependent on
the throttle opening - when closed it's essentially atmospheric as
mentioned above. That is also now a different path to the induction
system... past the throttle valve and there's no air mixed with the blow-by
gas. IOW you've lost the metered air-leak.

You will not be able to operate an engine in that condition for long before
you have serious problems with the intake manifold and its various
precision components, chambers and narrow tubes. Your throttle butterfly
is going to get in a helluva mess and the rubber intake tube is not oil
resistant rubber - it'll rot.

>The main purpose of the PCV valve is to ensure that one end of the breather
>system always has a lower pressure than the other, so that one end will
>always be an intake, and one will always be an outlet. That is why it has a
>variable orifice.
>
>
>
>> BTW
>> I'm quite sure that a PCV can fail in more ways than getting plugged
>> up - e.g. the spring can get gunked up and bind.
>
>
>
>How is this different from being "plugged up"?
>
>The PCV plunger is surrounded by the spring. The metered orifice is the
>SPACE around the coils of the spring. If the spring gets gunked up, then
>the orifice is reduced, becuase the orifice IS around the spring.

If the spring binds, the valve may not be able to float and jam in the
fully open or fully closed position... or anything in between. Most likely
it will float and stick intermittently initially.

>> The PCV lives an
>> environment which is not kind to metal or even plastics.
>
>
>
>And it is made of metal and oil-compatible plastics. You don't think they
>would think of doing that?

Take a look at a used one - there's oil emulsion (acids), lacquering and
even fine particulates in there. Combustion gases mixed with oil mist and
water vapor takes more than "oil compatible" materials to stand up.

>>
>> I'm quite sure that the reason the rubber plug at the end of the
>> exhaust camshaft of an Integra, next to the distributor, gets pushed
>> out is because of crankcase pressure increase. It seems to happen
>> more in Winter when the PCV can get frozen up.
>
>
>
>It happens because the rubber gets old and has reduced holding power,
>especially when cold. It is only really clamped in place by the two little
>ridges on it anyway. This explained to me by my Japanese mechanic. I
>replaced my leaky old one a few years ago. It has not leaked since.

Absolutely not. You can put a new plug in, in say October, and it'll be
pushed out slightly by end of Winter. The rubber is not old or perished in
any way. I do not need some mechanic to explain to me how this works -
I've replaced the plug twice myself and seen the condition of the rubber on
two different cars. In fact I suspect that just cleaning up the old plug
would work as well as a new one - once the oil has worked its way past the
ribs on the plug, which is BTW only encouraged by pushing it back in, it
has established a path to escape.

>In order for pressure to build to the point where it could possibly "push
>the plug out", BOTH the PCV AND the breather MUST be blocked.

Take your oil filler cap off with the engine running and feel the pulsing
of err, pressure. It is not a static even pressure. Note that pulsing is
there even if you had no blow-by at all and in all engines except for a
very few V configurations; add in blow-by and reduced capacity to extract
it and the pressure oscillation is increased as well as the max crankcase
pressure.

If both breather and PCV were blocked you'd blow out seals in a very short
space of time.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

Tegger® wrote:
> "Caroline" <caroline10027remove@earthlink.net> spake unto the
> masses in
> news:BmSxc.8651$uX2.7052@newsread2.news.pas.earthl ink.net:
>
>
>
> Note to Caroline: This time, please do not remove the
> cross-posting. I want as many minds involved in this debate as
> possible.

Fer Pete's Sake, TeGGeR, let it die. Crossposting is classic
trolling.
--

- Philip @ Maximum Torque RPM

"Tegger®" <teggeratistopdotcom@changetheobvious.invalid> wrote
> "Caroline" <caroline10027remove@earthlink.net> spake
snip
> Note to Caroline: This time, please do not remove the cross-posting. I want
> as many minds involved in this debate as possible.

I want misinformation (yours) spread as little as possible.

I'll try to respond to those who join us here at rec.autos.makers who seem to be
in the know, rational, open-minded, and who haven't had a response from others.

You can quote away in the other newsgroups. At some point, it's likely I'll
provide all the citations I provided earlier to help persuade people of the
truth that a malfunctioning PCV valve may (1) affect fuel economy and (2) may
cause excessive crankcase pressures, causing certain oil seals to fail
prematurely.

> > "Tegger®" <teggeratistopdotcom@changetheobvious.invalid> wrote
> >> "Caroline" <caroline10027remove@earthlink.net> spake
> >> > For the rational among us trying to learn about pressure: Think of
> >> > the crankcase as a bucket of water being fed with a hose but also
> >> > having two holes in the bottom of it. The rate of water flow and
> >> > the hole sizes are such that 4 inches of water are maintained in
> >> > the bucket with this setup. If one suddenly plugs one of the holes,
> >> > what happens to the water level in the bucket?
>
> >> A much more accurate analogy:
> >> Imagine a bucket with ONE hole in the bottom (NEVER plugged).
> >
> > = the breather hose (which is far far less likely to become plugged
> > than the PCV valve)
snip junk

> If our analogy is to be the bucket with a hole in the bottom, then the top
> of the bucket is the throttle inlet and the bottom of the bucket is the
> intake valve.

This does not work, as it does nothing to explain what is happening in the
crankcase.

> The PCV system has nothing to do with either the throttle or the intake
> valve.

If one is going to consider in detail the relative pressures involved, yes it
does.

> It simply redirects some of the clean intake gas to the crankcase,

.... at low load on 91 Honda Civics (among other models) via the breather hose.
Agreed.

> where it picks up blowby, and then directs it back to the intake again

.... via a PCV valve which meters the flow according to intake manifold vacuum.

At low load and with a PCV valve that has failed shut (for whatever reasons),
you're assuming that the flow described above reverses. But you can't assume the
breather hose can accomodate the blow by the way the PCV valve can.

Just because the pressure in the crankcase is now higher than where the breather
hose connects to the air intake does not at all mean the crankcase will be
purged to the same extent it is with a correctly functioning PCV valve.

> My anology (countering your erroneous one) has two holes in the side of the
> bucket, both in the water, but one above the other with a hose connecting
> the two. Absent the blowby, that IS a PCV system. It's just a redirector.

I still have no idea what denotes crankcase pressure in your system.

> The PCV system does not go to a second intake valve, which is what you
> conceptually imply with YOUR analogy of a bucket with two holes in the
> bottom.

My analogy illustrates flow directions and relative pressures correctly for a
1991 Honda Civic (and no doubt other Hondas) at WOT (wide open throttle). Yours
doesn't illustrate it at any load, from what I can tell.

> > Your pressure relationships do not mimic those in an actual PCV
> > system.
>
> Neither do yours. Your bucket analogy consists of a non-compressible fluid
> (water) being PUSHED into a container (bucket).

Again, my model assumes the level of the water denotes crankcase pressure.

Note: My model is only for the purposes of illustrating why crankcase pressure
may rise with a plugged PCV valve. It does not capture all the nuances of a PCV
system.

> The actual intake system of
> a car uses a compressible fluid which is SUCKED into the engine.
>
> The intake tract pressure is ALWAYS less than ambient with the engine
> running. Hence, in a normal engine, there is ordinarily SUCTION at BOTH
> ends of the PCV system.

Nope. On a 1991 fuel injected Civic (as well as other cars):

At low throttle:
--breather hose flow is from air intake (near the air filter) to the crankcase.
-- PCV hose flow is from crankcase to air intake (near the cylinders' air
intake valves)

At wide open throttle:
-- breather hose flow is from crankcase to the air intake (near the air filter)
-- PCV hose flow is zero, because the PCV valve is shut.

http://tinyurl.com/yrq9s (Autozone repair guide) says this, too. It reproduces
exactly what is said in my Chilton's manual for 1991 Civics. Note: Figure 1 at
this site is also for 1991 1.5 Liter FI Civics.

> It is necessary to use a restrictor valve to lower
> pressure at one end to make sure the flow is always in one direction.
>
> That's the PCV valve.
>
> Are you familiar with the venturi principle? That's all the PCV valve does.

Wrong.

The PCV valve does not employ the Venturi principle. Flow through the valve is
due merely to (1) the appropriate pressure differential that causes the valve's
control mechanism to open it; and (2) a pressure difference from crankcase to
PCV valve outlet (which would cause fluid flow through any hose/pipe/whatever).

Practical application of the Venturi principle generally involves two different
flows of fluids. Fluid 1 will pass through an orifice (a.k.a. Venturi channel)
of some kind. The orifice increases Fluid 1's velocity but reduces the pressure
(conservation of energy; Bernoulli principle). Near the discharge of the
orifice, Fluid 2 enters via a connected pipe (or hose, or whatever). Fluid 1
draws Fluid 2 into its flow, and they now mix together.

Parts of carburetors, for one, use the Venturi principle to draw gasoline flow
(Fluid 2) into the flow of fresh air (Fluid 1).

There is no such setup in the PCV system.

> <snip quotes from TV personalities saying that heavy blowby will overwhelm
> the PCV system>
>
> Well, yes, all undoubtedly true. But this has never been part of the
> discussion.

In this part of the thread, we were only discussing how crankcase pressure may
rise above normal (on average) with a plugged PCV valve.

I see you are now conceding this point.

> What has any of that got to do with your contention of
> reduction in gas mileage from a plugged PCV valve?

That's another part of the thread. I have not joined this, as we did in fact
discuss this to some extent a few weeks ago. My citations and summary
explanations speak for themselves. But you want to re-engage, so...

You are convinced the ECU's proper functioning in open and closed loop has no
dependence on how the correct operation of the PCV valve.

I on the other hand am convinced that in either open loop, closed loop, or both,
the ECU's proper functioning depends on a certain design flow through the PCV
valve. For example, with a failed shut PCV valve, the ECU has planned for a
certain response to (intake) manifold air pressure changes *assuming* a certain
flow through the PCV valve is occurring.

You seem to be rebutting, "But in closed loop (O2 sensor in play, providing
feedback), if the response is 'wrong,' the O2 sensor will see the wrong level of
O2 in the exhaust and send a (too rich) feedback signal to the ECU. The ECU will
adjust the air/fuel ratio for optimal economy."

But how does the ECU do this? In my 1991 fuel injected Civic, the ECU uses
signals from the MAP (manifold air pressure) sensor and crank angle sensor to
control fuel injector "basic discharge duration." The ECU's memory has pre-set,
fixed fuel injector "basic discharge durations" depending on these two inputs.
The fact that these basic discharge durations are pre-set and fixed means they
assume a certain flow from the PCV valve is present.

The O2 sensor's signal (among other sensors' signals) will modify the basic
discharge duration somewhat, but the engine is still stuck with a particular,
basic discharge duration. The pre-set values are not appropriate for a no-flow
condition through a malfunctioning PCV valve.

http://tinyurl.com/22d46 describes the general setup of a 91 Civic LX Programmed
Fuel Injection system. The remarks above about "basic discharge duration," etc.
derive from it and my own engineering experience.

The above is one explanation of why in closed loop fuel economy may be bad with
a malfunctioning PCV valve.

"George Macdonald" <fammacd=!SPAM^nothanks@tellurian.com> wrote
snip
> If the spring binds, the valve may not be able to float and jam in the
> fully open or fully closed position... or anything in between. Most likely
> it will float and stick intermittently initially.

I concur with this analysis of what may happen when a PCV valve gets gunk in it.
"Clogging" may result in either a fail open, fail shut, or fail "intermediate"
condition.

The rest of George's analysis looks fine to me as a general description. I do
note that, for one, the 1991 Civic does not, from what I can tell, have a mass
air flow sensor. The car (like many cars) has other minor idiosynchrasies that
distinguish it from George's description.

I hope we all agree that there is some variation from one car model's PCV system
to another and so are somewhat generous when reviewing descriptions of flow
directions, among other features.

"Caroline" <caroline10027remove@earthlink.net> wrote
> My analogy illustrates flow directions and relative pressures correctly for a
> 1991 Honda Civic (and no doubt other Hondas) at WOT (wide open throttle).

Oops. Not.

At WOT, on the 91 Civic by design the PCV valve is shut, and crankcase gases by
design exit through the breather hose.

At non-WOT, on the 91 Civic by design the PCV valve is generally open at least
partly.

My model is simply illustrating that pressure will rise in the crankcase when an
ordinarily open escape path (the PCV valve or its hose) is blocked.

This is the same as blocking off one or more exit holes in the bottom of a
bucket of water previously being filled such that the rate of water entry = the
rate of water exit, and such that the system maintains a certain level of water
in the bucket. Goes ins = goes outs, as we used to say in the nuclear navy. But
block off an exit hole, and the level of water rises, just as average crankcase
pressure rises when blocking off the PCV line.

Tegger can argue that at WOT, the PCV valve is supposed to be fully shut, and
crankcase gases exit via the breather hose, by design. So a blocked PCV valve on
a 91 Civic has no effect at WOT.

But how often is a car at WOT?

Certainly not all the time.

On Thu, 10 Jun 2004 17:15:06 GMT, "Caroline"
<caroline10027remove@earthlink.net> wrote:

>"George Macdonald" <fammacd=!SPAM^nothanks@tellurian.com> wrote
>snip
>> If the spring binds, the valve may not be able to float and jam in the
>> fully open or fully closed position... or anything in between. Most likely
>> it will float and stick intermittently initially.
>
>I concur with this analysis of what may happen when a PCV valve gets gunk in it.
>"Clogging" may result in either a fail open, fail shut, or fail "intermediate"
>condition.
>
>The rest of George's analysis looks fine to me as a general description. I do
>note that, for one, the 1991 Civic does not, from what I can tell, have a mass
>air flow sensor. The car (like many cars) has other minor idiosynchrasies that
>distinguish it from George's description.

Some mfrs, notably those with Bosch FI systems, use a mass airflow sensor -
often a hot-wire thermistor AFAIK. Honda derives mass flow, I assume in
the ECU programming, from throttle position, intake air temp and manifold
absolute pressure. Note that those actual measurements can also be used
for other programmable parameters of the ECU.

>I hope we all agree that there is some variation from one car model's PCV system
>to another and so are somewhat generous when reviewing descriptions of flow
>directions, among other features.


I think there are some which just have to be wrong though - possibly
outdated? IMO the Toyota doc (h63.pdf) looks the best explanation.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

On 10 Jun 2004 01:37:36 GMT, "Tegger®"
<teggeratistopdotcom@changetheobvious.invalid> wrote:

>George Macdonald <fammacd=!SPAM^nothanks@tellurian.com> spake unto the
>masses in news:bc8fc0dfrepdi5jr189vm8mcckpfanrlbd@4ax.com:
>
>
>> Look I don't really care what your mechanic says. I've been told enough
>> guff by mechanics over the years to fill an encyclopaedia.
>
>
>
>So you throw the baby out with the bathwater. They're ALL bad, right?

They're not *all* bad - good ones who are honest with the customer are
rare... IME.

>> The computer hasn't measured the mass of leaked air
>
>
>
>It's NOT "leaked air". It's the very same air that has already passed by
>the throttle plate and the air flow meter.

No it has *not*. As already mentioned umpteen times, the breather tube
intake is *upstream* of the throttle plate; geez you told me to look at my
car but you haven't even done as much yourself! BTW there is no air flow
meter in the Honda systems that I've seen.

>All the PCV valve does is make sure that flow is always present, and always
>in one direction.
>
>This is the part nobody in this group seems to understand. Of course,
>nobody in this group is a working mechanic, either (me included). And some
>of them aren't even willing to listen to what working mechanics have to
>say.

I guess we just know better.:-) See above.

>> So your mechanics are right and the auto mfrs and engine designers are
>> all wrong.<shrug>
>
>
>
>Show me ANYWHERE where ANY auto mfr and engine designer says HOW MUCH the
>engine will "run rich" with a plugged PCV valve.

Not exactly but in the h63.pdf, a Toyota doc, it states quite plainly: "The
installation of an incorrect valve may cause engine stalling, rough idle
and other driveability complaints". It's not a big hop to conclude that a
malfunctioning PCV is an err, incorrect valve.

>I think you guys are all misunderstanding what those auto mfrs and engine
>designers are saying. Web pages don't count here.

Just RTFM... the service manual and apply a bit of scientifically informed
interpretation.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

"George Macdonald" <fammacd=!SPAM^nothanks@tellurian.com> wrote
> <caroline10027remove@earthlink.net> wrote:
> > I do
> >note that, for one, the 1991 Civic does not, from what I can tell, have a
mass
> >air flow sensor. The car (like many cars) has other minor idiosynchrasies
that
> >distinguish it from George's description.
>
> Some mfrs, notably those with Bosch FI systems, use a mass airflow sensor -
> often a hot-wire thermistor AFAIK. Honda derives mass flow, I assume in
> the ECU programming, from throttle position, intake air temp and manifold
> absolute pressure. Note that those actual measurements can also be used
> for other programmable parameters of the ECU.

Yes. Perhaps you're also getting at the fact that fuel/air ratio is not the only
closed loop controlled engine parameter. A certain Ford service manual I was
reading the other day noted that engine RPM control is also closed loop: The
actual RPM is fed back to the computer and compared to the desired RPM, and the
computer responds to adjust the RPM.

The overlap of these closed loop engine control systems is inevitable of course.
The modeling is sophisticated and probably proprietary. The latter comment is
based in part on having known a few PhD'd Ford control systems engineers who
work on emissions control design and implementation of the same. Not trying to
name drop; just trying to say there are of course people who have specific
model's full ECU control system model on paper (er, computer) and could give a
very precise and practical answer as to how the ECU responds to different
changes for that model. But access to this info by the public is difficult or
impossible. Plus, I for one no longer have access to a computer or software
capable of handling simulation of such complex models that might offer more
insight into the interactions of the systems.

So I think analyses here of how the ECU controls the engine can only be at a
very basic level.

> >I hope we all agree that there is some variation from one car model's PCV
system
> >to another and so are somewhat generous when reviewing descriptions of flow
> >directions, among other features.
>
> I think there are some which just have to be wrong though - possibly
> outdated? IMO the Toyota doc (h63.pdf) looks the best explanation.

For Toyotas, I agree. But one item that I think is impeding analysis here is
whether the PCV valve is wide open or fully shut at wide open throttle (WOT). I
am convinced (for now) that this does vary from one car make, model, and year to
another. All the designs still accomplish the same thing--removing crankcase
gases. But they are engineered differently. (I expect you know all this, but for
the sake of the written record... )

In support of this, at the library the other day I pulled down several car
makers' Chilton manuals. It's easy to turn to the first few pages of Section 4
"Emissions" to see specifically whether the PCV valve was wide open or fully
shut at WOT. Some of the manuals are a little vague on this point. Others are
not.

All or at least several models of Hondas and the early 1990s Acuras have the
PCV valve fully shut at WOT. The manuals explicitly add that the crankcase gas
flow at WOT is then exclusively out the breather hose to the air intake
(upstream of the throttle, like you noted in your other, recent post). Because
of this explicit statement, it does not seem like this is a mistake. It could
be. As you say, the manuals do have mistakes. But I'm not yet convinced.

By contrast, the reports for Toyotas (and some other makes) I've seen have the
PCV valve fully open at WOT.

Pressure differential and flow-wise, both the Toyota explanations and the Honda
explanations appear to me to be rational. Truly intelligent commentary on why in
one the PCV valve is shut and in the other it is open might demand more inside
knowledge of the systems than is available.

IIRC Mitsubishi engineers its PCV system setup quite differently from the other
manufacturers I read.

As your Toyota document http://www.autoshop101.com/forms/h63.pdf shows, some PCV
systems use a fixed orifice instead of a PCV valve. The orifice of course is not
as precise at metering in accord with engine load.

SHO Ford Tauruses from 1986-1995 do not even have a PCV valve nor apparently
orifice. (I was recently helping a relative with fuel mileage concerns on his
Taurus, thus I've been reading about its PCV system design too.)

I suspect the extent to which fuel mileage may be affected by a malfunctioning
PCV system will vary, and possibly quite a lot, from one car make to another.

Nonetheless, for the readers here, my understanding is that a properly
functioning PCV system first and foremost ensures the crankcase vapors are kept
to a minimum. I'd say at a minimum for all cars the engine oil may become
dirtier sooner with a malfunctioning PCV system. This by itself warrants its
inspection and/or replacement as a routine maintenance item. If fuel mileage
drops off, it's also certainly worth considering replacement/cleaning of the PCV
valve.

Treatise over.

On Sat, 12 Jun 2004 18:27:27 GMT, "Caroline"
<caroline10027remove@earthlink.net> wrote:

>"George Macdonald" <fammacd=!SPAM^nothanks@tellurian.com> wrote
>> <caroline10027remove@earthlink.net> wrote:
>> > I do
>> >note that, for one, the 1991 Civic does not, from what I can tell, have a
>mass
>> >air flow sensor. The car (like many cars) has other minor idiosynchrasies
>that
>> >distinguish it from George's description.
>>
>> Some mfrs, notably those with Bosch FI systems, use a mass airflow sensor -
>> often a hot-wire thermistor AFAIK. Honda derives mass flow, I assume in
>> the ECU programming, from throttle position, intake air temp and manifold
>> absolute pressure. Note that those actual measurements can also be used
>> for other programmable parameters of the ECU.
>
>Yes. Perhaps you're also getting at the fact that fuel/air ratio is not the only
>closed loop controlled engine parameter. A certain Ford service manual I was
>reading the other day noted that engine RPM control is also closed loop: The
>actual RPM is fed back to the computer and compared to the desired RPM, and the
>computer responds to adjust the RPM.
>
>The overlap of these closed loop engine control systems is inevitable of course.
>The modeling is sophisticated and probably proprietary. The latter comment is
>based in part on having known a few PhD'd Ford control systems engineers who
>work on emissions control design and implementation of the same. Not trying to
>name drop; just trying to say there are of course people who have specific
>model's full ECU control system model on paper (er, computer) and could give a
>very precise and practical answer as to how the ECU responds to different
>changes for that model. But access to this info by the public is difficult or
>impossible. Plus, I for one no longer have access to a computer or software
>capable of handling simulation of such complex models that might offer more
>insight into the interactions of the systems.
>
>So I think analyses here of how the ECU controls the engine can only be at a
>very basic level.

True and I don't have inside info on those particular aspects of auto
design for any mfr. I'm pretty sure though that after all the theoretical
behaviors have been modeled and optimized, the production model programming
of the ECU is subject to fine adjustments based on empirical testing for
low emissions.

>> >I hope we all agree that there is some variation from one car model's PCV
>system
>> >to another and so are somewhat generous when reviewing descriptions of flow
>> >directions, among other features.
>>
>> I think there are some which just have to be wrong though - possibly
>> outdated? IMO the Toyota doc (h63.pdf) looks the best explanation.
>
>For Toyotas, I agree. But one item that I think is impeding analysis here is
>whether the PCV valve is wide open or fully shut at wide open throttle (WOT). I
>am convinced (for now) that this does vary from one car make, model, and year to
>another. All the designs still accomplish the same thing--removing crankcase
>gases. But they are engineered differently. (I expect you know all this, but for
>the sake of the written record... )
>
>In support of this, at the library the other day I pulled down several car
>makers' Chilton manuals. It's easy to turn to the first few pages of Section 4
>"Emissions" to see specifically whether the PCV valve was wide open or fully
>shut at WOT. Some of the manuals are a little vague on this point. Others are
>not.
>
>All or at least several models of Hondas and the early 1990s Acuras have the
>PCV valve fully shut at WOT. The manuals explicitly add that the crankcase gas
>flow at WOT is then exclusively out the breather hose to the air intake
>(upstream of the throttle, like you noted in your other, recent post). Because
>of this explicit statement, it does not seem like this is a mistake. It could
>be. As you say, the manuals do have mistakes. But I'm not yet convinced.

Chilton's manual says this? They are notorious for being full of mostly
generic info/pages supplemented by a few token pages for the specific model
at hand. The one I got for my VW Beetle had a section on replacing
coolant.<shrug>

I have Helm manuals for '88 Integra, '90 Civic, '92 Integra, '99 Integra
and 2K Accord and none of them go into details on exact behavior of the PCV
valve - all have just the simple hose pinch check for verification of
functionality. I'd like to know where Chiltons got their info from and how
they arrive at their conclusion - frankly I have my doubts about their
accuracy.

>By contrast, the reports for Toyotas (and some other makes) I've seen have the
>PCV valve fully open at WOT.
>
>Pressure differential and flow-wise, both the Toyota explanations and the Honda
>explanations appear to me to be rational. Truly intelligent commentary on why in
>one the PCV valve is shut and in the other it is open might demand more inside
>knowledge of the systems than is available.

The illustrations of PCVs in the Honda Helm manuals, though small, look
very similar to the one in the Toyota h63.df doc, with a pintle being
sucked at high manifold vacuum into a restricted neck, floating somewhere
in the middle of its travel at low load cruising and being very close to
closed at high load. That last condition where the spring is *almost*
fully extended provides the least restriction at the pintle end of the
valve and therefore the highest flow of blow-by gas.

Toyota notes that in that last condition, if blow-by exceeds the PCV's
ability to flow the gases, they will take the route of the breather hose.
This all makes sense to me.

>IIRC Mitsubishi engineers its PCV system setup quite differently from the other
>manufacturers I read.
>
>As your Toyota document http://www.autoshop101.com/forms/h63.pdf shows, some PCV
>systems use a fixed orifice instead of a PCV valve. The orifice of course is not
>as precise at metering in accord with engine load.
>
>SHO Ford Tauruses from 1986-1995 do not even have a PCV valve nor apparently
>orifice. (I was recently helping a relative with fuel mileage concerns on his
>Taurus, thus I've been reading about its PCV system design too.)
>
>I suspect the extent to which fuel mileage may be affected by a malfunctioning
>PCV system will vary, and possibly quite a lot, from one car make to another.
>
>Nonetheless, for the readers here, my understanding is that a properly
>functioning PCV system first and foremost ensures the crankcase vapors are kept
>to a minimum. I'd say at a minimum for all cars the engine oil may become
>dirtier sooner with a malfunctioning PCV system. This by itself warrants its
>inspection and/or replacement as a routine maintenance item. If fuel mileage
>drops off, it's also certainly worth considering replacement/cleaning of the PCV
>valve.

I'll add that a PCV which is not allowing sufficient flow is going to cause
accelerated deterioration of the components of the induction system: the
rubber intake hose, throttle valve, EACV, fast idle valve and any other
vacuum driven items. Besides the usual hose pinch check, it's also worth
checking the rubber intake hose where the breather pipe enters it for oily
emulsified mess as a guide to whether the PCV needs replaced.

>Treatise over.

Chiltons notwithstanding, I think we're in agreement.:-)

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

"George Macdonald" <fammacd=!SPAM^nothanks@tellurian.com> wrote
> <caroline10027remove@earthlink.net> wrote:
>
> >"George Macdonald" <fammacd=!SPAM^nothanks@tellurian.com> wrote
> >> <caroline10027remove@earthlink.net> wrote:
> >> > I do
> >> >note that, for one, the 1991 Civic does not, from what I can tell, have a
> >mass
> >> >air flow sensor. The car (like many cars) has other minor idiosynchrasies
> >that
> >> >distinguish it from George's description.
> >>
> >> Some mfrs, notably those with Bosch FI systems, use a mass airflow sensor -
> >> often a hot-wire thermistor AFAIK. Honda derives mass flow, I assume in
> >> the ECU programming, from throttle position, intake air temp and manifold
> >> absolute pressure. Note that those actual measurements can also be used
> >> for other programmable parameters of the ECU.
> >
> >Yes. Perhaps you're also getting at the fact that fuel/air ratio is not the
only
> >closed loop controlled engine parameter. A certain Ford service manual I was
> >reading the other day noted that engine RPM control is also closed loop: The
> >actual RPM is fed back to the computer and compared to the desired RPM, and
the
> >computer responds to adjust the RPM.
> >
> >The overlap of these closed loop engine control systems is inevitable of
course.
> >The modeling is sophisticated and probably proprietary. The latter comment is
> >based in part on having known a few PhD'd Ford control systems engineers who
> >work on emissions control design and implementation of the same. Not trying
to
> >name drop; just trying to say there are of course people who have specific
> >model's full ECU control system model on paper (er, computer) and could give
a
> >very precise and practical answer as to how the ECU responds to different
> >changes for that model. But access to this info by the public is difficult or
> >impossible. Plus, I for one no longer have access to a computer or software
> >capable of handling simulation of such complex models that might offer more
> >insight into the interactions of the systems.
> >
> >So I think analyses here of how the ECU controls the engine can only be at a
> >very basic level.
>
> True and I don't have inside info on those particular aspects of auto
> design for any mfr. I'm pretty sure though that after all the theoretical
> behaviors have been modeled and optimized, the production model programming
> of the ECU is subject to fine adjustments based on empirical testing for
> low emissions.

Absolutely.

I recall the academic folks I mention above giving Christmas presents to the
techs in the Ford motors emission controls labs, where new "on paper/computer"
designs and theory were being implemented. They all worked that closely. (Not
sure how they got along, but they definitely had verbal communications.)

snip
> >All or at least several models of Hondas and the early 1990s Acuras have the
> >PCV valve fully shut at WOT. The manuals explicitly add that the crankcase
gas
> >flow at WOT is then exclusively out the breather hose to the air intake
> >(upstream of the throttle, like you noted in your other, recent post).
Because
> >of this explicit statement, it does not seem like this is a mistake. It could
> >be. As you say, the manuals do have mistakes. But I'm not yet convinced.
>
> Chilton's manual says this?

Yes. The Autozone online repair guides repeat it.

> They are notorious for being full of mostly
> generic info/pages supplemented by a few token pages for the specific model
> at hand. The one I got for my VW Beetle had a section on replacing
> coolant.<shrug>

I've never had a Helm manual in my hands. Someone here recently said the manual
pages accessible via
http://www.honda.co.uk/owner/workshopmanuals2.html were identical to Helm. While
I realize manuals in general are full of errors (inaccuracies?), I don't see
anymore in my Chilton's than I do at the link above.

One matter over which I'm a little anal right now is how neither Chilton's nor
the UK site manuals above talk about removing the cruise control actuator for
their 1991 Hondas in the timing belt instructions. The UK site manuals only seem
to have caught onto the necessity of this step in the 1995 or so model year
Hondas. (Haven't checked the 1996 Chilton manuals yet.)

OTOH, you have been reading these various manuals longer than I and have the
Helm manual in your hands, so of course I recommend readers defer to your
experience on this.

> I have Helm manuals for '88 Integra, '90 Civic, '92 Integra, '99 Integra
> and 2K Accord and none of them go into details on exact behavior of the PCV
> valve -

They don't say that the opening of the PCV valve is proportional to intake
manifold vacuum?

E.g. from http://www.honda.co.uk/owner/CivicManual/pdf/11-109.pdf for 1995-1997
Civics:
"When the engine starts, the plunger in the PCV Valve is lifted in proportion to
intake manifold vacuum... "

> all have just the simple hose pinch check for verification of
> functionality. I'd like to know where Chiltons got their info from and how
> they arrive at their conclusion - frankly I have my doubts about their
> accuracy.

Not to drag this out too much, but I'm figuring at the moment that at WOT,

-- blowby gas production is at its maximum.
-- average crankcase pressure is likely at its maximum

Where things become confusing is when assessing the pressures at

-- the breather hose's connection to the air intake, just upstream of the
throttle. This absolute pressure should decrease as the throttle is opened.

-- the PCV valve connection to the air intake, downstream of the throttle
(should be a varying vacuum; lower vacuum = higher abs. pressure at WOT, at
least for Honda's systems)

I figure on Hondas, at WOT, the differential pressure from crankcase to breather
hose connection meters (or just accomodates) the flow well, by design. The Honda
PCV valve shuts.

On Toyotas at WOT, the differential pressure operating the PCV valve and the
valve design meters the flow well. The Toyota PCV valve stays open at WOT(??)
but is assisted by the breather hose?

> >By contrast, the reports for Toyotas (and some other makes) I've seen have
the
> >PCV valve fully open at WOT.
> >
> >Pressure differential and flow-wise, both the Toyota explanations and the
Honda
> >explanations appear to me to be rational. Truly intelligent commentary on why
in
> >one the PCV valve is shut and in the other it is open might demand more
inside
> >knowledge of the systems than is available.
>
> The illustrations of PCVs in the Honda Helm manuals, though small, look
> very similar to the one in the Toyota h63.df doc, with a pintle being
> sucked at high manifold vacuum into a restricted neck, floating somewhere
> in the middle of its travel at low load cruising and being very close to
> closed at high load.

To be very clear, I recognize two valve "seats" in the PCV valve. The Toyota
drawing's bottom seat is pretty much an "all or nothing" seat design. The Toyota
drawing's upper seat is designed to regulate in accord with pintle position.

So above I hope you mean the bottom of the pintle in the drawings at high load
is almost touching its seat. At the same time, the top portion of the pintle's
location is such that the second, upper valve passage is as wide open as
possible.

As load increases and the bottom of the pintle nears the bottom in the drawings,
the flow through the valve may be followed by tracing the valve flow
characteristic curve (page 2) leftwards, until the peak valve flow is reached.
Continuing left there is a quick dropoff on the curve.

The Toyota valve's flow always stays above the blowby curve?

The Honda valve's flow drops below the blowby curve.

Unless of course Honda Chilton's is all screwed up.

> That last condition where the spring is *almost*
> fully extended provides the least restriction at the pintle end of the
> valve and therefore the highest flow of blow-by gas.

Agreed.

> Toyota notes that in that last condition, if blow-by exceeds the PCV's
> ability to flow the gases, they will take the route of the breather hose.
> This all makes sense to me.

Same here, except the Toyota site isn't clear about whether the PCV valve
actually closes (as its characteristic curve implies, somewhat) at WOT.

snip
> I'll add that a PCV which is not allowing sufficient flow is going to cause
> accelerated deterioration of the components of the induction system: the
> rubber intake hose, throttle valve, EACV, fast idle valve and any other
> vacuum driven items.

Due to oily acidic(?) exhaust compounds accumulating on parts?

> Besides the usual hose pinch check, it's also worth
> checking the rubber intake hose where the breather pipe enters it for oily
> emulsified mess as a guide to whether the PCV needs replaced.

> >Treatise over.
>
> Chiltons notwithstanding, I think we're in agreement.:-)

Yes.