Evaporative Emissions Purge Solenoid

The factory Rover evaporative emissions carbon canister purge solenoid was originally 'modulated' on and off when coolant temp is above 70c, engine is above 1500rpm and MAP below 30kpa.

Documentation found on Rover MEMS control strategy

CFSV actuation occurs when

When the CFSV is actuated by MEMS, the valve is modulated on and off

and fuel vapours are drawn into the inlet manifold to be burnt by the engine during normal combustion. So that engine performance will not be affected, the CFSV remains closed during cold engine operation and also during engine idle (makes sense indeed).

Using a diagnostic tool to access the Rover MEMS ECU live parameters, there is a page that shows 'Purge Duty' as 56%. This value never seemed to change in all the times I ever reviewed it. For lack of information on this function I will make the assumption that this is the duty cycle of the purge solenoid. Whether this value changes for different engine speeds is unknown at this time, so will simply assume a fixed value at this time.


Previously, going back to firmware 1.0.73 I simply energised the solenoid on RPM and MAP. slightly later firmware releases up to 1.1.47 and beyond introduced the coolant temp into the Misc output config which helped. I've not had this car running since 2010 and a lot has changed in firmware since!!


I intend to use secondary PWM in Absolute mode and configure 56% duty above 1500rpm, below 6000rpm and below 30kpa (~engine breaking). I had thought about using Misc2 output to energise a relay to cut the 12v feed to the solenoid based on coolant temp alone to emulate the original Rover strategy, but the extra hardware and wiring doesn't justify it in this application. It would be neat to add a function in the Firmware to allow Misc output to function through the secondary PWM table, but I'm happy enough the way it is at the moment.

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