HAILERS

So, I wonder if I know how the Purge Valve really works. If the valve opens by a vacuum being put on the nipple on top of the valve (and that is the way the thing works), then why isn't the hose connected to the top of the valve going to a source AFTER the throttle bodies instead of what the pictures show, which is its going to a source BEFORE the throttle bodies.

And it shows the bottom vacuum line going to a source AFTER the throttle body. That hose is the one that is to suck the fumes out of the big line attached to the bottom of the Purge Control Valve.

The bottom line is that I don't think there is squat in terms of suck/vacuum in FRONT of the throttle body............so the dang thing should not work or the picture is drawn wrong...one.

hugues

It seems the bottom of the purge valve connects to the vacuum source (after the plates) and the top connect to atmospheric pressure air (before the plates).

When the valve opens, the fumes and intake air are drawn to the bottom hose of the purge valve into the intake tract after the plates.

You need a connection to air before the plates (top hose) so that the fumes can be mixed with intake air.

To be more precise, the pressure differential between vacuum and atmospheric pressure draws air into the valve which "sucks" along the blow-by fumes.

Well, that's my take on it. I could be wrong.

hugues -

hugues

[Please, disregard my previous post, it does not make too much sense]

After thinking about it,

I think the normal route of the blow-by gases is from the oil filler neck port (bottom of purge valve 1) to the vacuum port (bottom of purge valve 2).

If there is too much blow-by gases (heavy load), the valve allows the blow-by gases to go to the "before the plates" port where they can be mixed with intake air, kinda like a breather hose setup on piston engine with regular vacuum operated PCV valve.

When idling and low load, the valve is kept closed and no blow-by gases can go back to the combustion chambers or intake.

hugues -

HAILERS

1. There is no passage between the top nipple and the two bottom nipples.

2. The two bottom nipples are not connected to each other unless the airpressure in the upper part of the valve is less than the bottom part of the valve and there is enough pressure in the bottom half to over come the spring pressure that is holding the diaphram closed.

3. I've blown in the bottom nipples. They are blocked unless I put a vacuum on the top nipple.

4. Got me on how it works.

hugues

We know that under high manifold vacuum (idle), we don't want the purge valve to be open too much. So it makes sense to not put the hose that controls the purge valve opening past the throttle plates. At idle, before the plates, there is little vacuum. After the plates, the vacuum is very high and that would make the purge valve open way too much if the top hose connects there.

The purge valve should be fully open under heavy load, that is wide open throttle. That should be achieved whether the hose connects before or after the plates, since the vacuum should not differ much before or after the plates.

I think it makes sense somehow.

HAILERS, thanks for pointing out that the top port does not connect to the bottom one. Now that I Iook at the diagram of the system in the Haynes manual, it clearly shows how it is supposed to work like you describe.

Hugues -

HAILERS

Only one real problem there. When the throttle is wide open .......there is not much of a vacuum at all. Look at your vacuum gauge or your aftermarket boost gauge or even the stock boost gauge. I even went so for about a year ago to run a long vacuum hose to a nipple before the throttle plates and put the darn thing in my mouth while driving. Never even felt the slightest vacuum.

If I'm wrong, let me know. Keep the answers coming. I thought maybe the crankcase pressure might build up enough to raise the poppet in the valve thereby opening the passage b/t the two bottom hose.....but thats asking it to overcome the spring pressure. Nope.

NZConvertible

OK, here's my take on all this. Forgive me if I repeat anything said previously.

As per the FSM, "at idle the purge control valve is opened slightly and a small amount of blow-by gas is drawn into the dynamic chamber and burned. At high engine speed or heavy-load condition, the purge control valve is opened further and a larger amount of blow-by gas is drown (sic) into the dynamic chamber."

So the idea here is to apply a constant vacuum to the sump, to remove blow-by gases. But we don't want to suck it in too fast, as that would probably effect engine performance and instantaneous emissions, so the purge control valve acts a bit like a throttle, regulating the rate at which the engine re-ingests blow-by gases (hence its name). If you look really closely at the schematics, you can see that the higher the pressure differential across the throttle (i.e. the further closed the throttle is), the further the valve is pulled closed by vacuum, which restricts airflow through it.

The same method is used to ventilate the charcoal cannister, but this really only applies at and just after start-up, when the vacuum from the purge valve sucks air through the charcoal cannister and pickes up all the fuel vapour absorbed from fuel tank evaporative emissions. Again you don't want to suck the fuel vapour in too quick, as a very rich mixture would result. The air and vapour is sucked in through the bottom of the oil filler pipe and out the top of it by the vacuum from the purge control valve

I guess the line to the TID takes care of any excess full-load blow-by pressure if the purge valve line can't flow enough. The check valve at the TID ensures intake air doesn't bypass the throttle, which would increase idle speed.

I don't claim this is 100% correct, it's just what I've deduced myself from studying the FSM.

hugues

I like your explaination NZ, I think it makes a lot of sense.

at wot, the pressure differential should be pretty much 0 across the plates, so the blow-by gases must be under enough pressure to overcome the spring pressure exerted on the diaphragm inside the valve, right ?

Hugues -

HAILERS

So.....I took mine apart. The fsm diagram isn't real accurate. If there is a vacuum on the small hose on the bottom it will pull on the diaphram and stop any fumes from being pulled into the intake. There will be no place for the fumes in the large hose to go.

If the throttle plates are open pretty far then there won't be any suction by that small hose on the bottom of the purge valve and the only thing keeping the path of gas from the large hose from going into that same small hose.....is the spring pressure shoving down on the diaphram keeping the passage shut.

So I guess if there is any pressure at that time in the large hose, that pressure will shove against the spring and open a passage as long as there is pressure in the sump. I guess I am/was overestimating how much spring force is there to keep the passage shut off.

jpg attached. The order from top to bottom is: The bottom half with the small hose attached.

The bottom of the diaphram.

Spring

The top half.

Scott 89t2

so what happens under boost? nothing moves through the vavle?

I think that's what the TID one is for. it says that route is for "high load" in the fSM. I think under boost any pan pressure goes that way. under vac it gets sucked into the UIM.

1SxyRXy

is that the thing that keeps gasses going to your oil stem filler thing to help keep the gases make the sluge that some people get?. if it is then somone just explained to me exactly how it worked today.