Re: Charcoal canisters


"Mark W" <s@o> wrote in message
news:46d6ffb0$1_3@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
My Nissan has a charcoal canister and there are four pipes:

One coming from the petrol tank, I assume this is the 'vapours'.
One at the bottom going back under the car, I assume this is for liquid
petrol to drain back into the tank.

Two at the top, one connected to manifold vacuum and one ending up (via
the EGR valve) at a vacuum valve solenoid.

The valve opens and closes to activate the EGR and suck fumes from the
canister at the same time, by the look of the system.

So I can't suck or blow through either of the latter two. Is that normal?
I suspect not!

Any reason you're checking this?

The usual set-up is three pipes.
Two on one end, and one at the other.
The two at one end, one will come from the tank (ie the vapour line), and
one will go to some form of control valve, then onto the engine inlet
manifold.
The other pipe is vented to atmosphere (usually runs back to around the
filler neck area).

The way it works, is as the tank warms up, the petrol vapour vents from the
tank, through the charcoal where the petrol vapour is filtered out by the
charcoal, before finally venting from the other end of the charcoal
canister.
When the engine is then started, the control valve is opened under certain
conditions, which causes ait to be drawn back in through the canister vent,
where it draws the fuel vapour out of the charcoal, before being drawn into
the engine and combusted.

The usual problem is for the vent pipe to become blocked (it's very rare for
the actual carbon canister to block), which causes the tank to be sucked in
under manifold vacuum.


I don't know why yours has four pipes, or why one goes via the EGR valve.


.

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