In reply to a message from Kirbert sent Mon 14 Nov 2016:
this has been copied and pasted from xj4o forums , from
bryan N
purge valve works like this.
When the ignition is turned on (engine not running) the
purge valve solenoid is energized to close it to prevent
vapor transfer from the carbon canister to the engine.
When running, the ECU triggers the purge valve to open
momentarily with each of a series of pulses starting with a
duration of about 10 milliseconds at idle RPM with a gap of
about 140 - 145 milliseconds between pulses giving a limited
vapor flow to the manifold. As engine speed increases, so
does the ‘pulse width’, increasing the valve opening time
with each pulse but not varying the gap between pulses to
give a proportionate increase in vapor flow per pulse with
increased RPM.
The good book illustrates this purge valve signal sequence
but I guess you would need a 'scope to see it. The book also
says ‘‘the purge valve operation at idle can be detected by
holding the valve in the palm of the hand’’ - that being the
extent of the purge valve ‘testing procedure’ as far as I
can see.
i think the only missing info here that the purge valve acts
like a check valve too , so since it stays open when not
energized it will not act like a big vacuum leak–
The original message included these comments:
Something must be VERY different, because on the 1980’s V12 the two
purge valves are vacuum-operated. There is no ECU involved. The two
–
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