I just checked my ECU data sheet and the signal to the evap control valve is pulsed - conditions are engine under load and engine hot - the pulse is 10 volt at 10ms
not sure if that is 10ms cycle time, or duty time, as I can't find the shot from the scope. This is much the same as my +8 where you can hear the valve tapping away.
Looks like pin 22 of the ECU feeds 12 volt to the valve, and pin 11 grounds the valve. So pin 11 has 12 volts on it until the engine is hot and under load when the ECU turns the valve on, at which point it probably goes down to something like 2 volts, then up to 12, then back to 2 and so on. Hence a 10 volt pulse across the valve
I double checked and confirmed there are no sensors, so the ecu will not know if there are vapors in the filter, but just goes through the pulsing routine to purge any that are there
The filter is a ford part, I have ordered one from ebay so I can study the vent valve. I assume that the filter must allow positive pressure to escape but trap any vapor. As on a hot day with the car at rest the petrol will vaporize, and needs to be vented. Then once the car is running the trapped vapor needs to be sucked into the engine, while retaining a level of vacuum on the tank.
