In reply to a message from sbobev sent Mon 23 Sep 2013:
Steve,
I’m not sure I’m quite tracking with you.
The Rochester valve controls vapor flow to the charcoal
canister. It has three functions, it provides fuel tank
pressure relief, fuel tank vacuum relief and vapor flow
control. It is controlled by vacuum from the intake manifold
when the engine is running and by fuel tank pressure when the
engine is off.
The two purge valves control the flow of vapor from the
canister to the intake manifold which purges the canister.
These valves are solenoid operated via a series of pulses from
the ECM. The solenoid is normally open and the ECM determines
when to ‘close’ the solenoid based on a load vs engine speed
strategy and only operates when fueling is in closed loop
mode. As the solenoid closes the valve allows vapor to flow.
So just because you don’t have a whoosh when you open the tank
does not necessarily mean the purge valves are working
properly.
I’m not sure about mechanically testing the valves. You can
hear them energise when the ignition is turned on and if you
hold them during closed loop operation you should be able to
verify they are working by feel but it doesn’t mean that they
are not leaking a little vapor in open loop mode. I would
think that you could put a handheld vacuum pump on the valve
with the engine running in open loop and see if vacuum holds?
Does this answer your question?
Also yes I own a 6 but have owned a number of Jags over the
years including an XJ12 which had the 6.0. Many of the
systems, such as evap control are identical between the 6 and
the 12 and many processes such as fueling use similar logic.
However, I am certainly no expert on the V12
Cheers,
Allan–
The original message included these comments:
Are we talking about the ‘Rochester’ valve here or the two
valves that are plumbed to both banks?
Closing the Rochester valve in order to purge the canister
is in order, otherwise the manifold vacuum will be sucking
the gas tank and collapsing it (well-documented issue)
I’ve had my gas tank lid open/closed during various test and
have not seen the ‘‘whoosh’’, so, I believe my EVAP system is
OK.
–
1994 XJS 4.0 2+2 Convertible Factory 5 Speed Manual
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