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Torque » Torque OBD ECU Scanner » Torque Discussion / Ideas » EVAP SYSTEM

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Author Topic: EVAP SYSTEM
Posts: 1
on: February 11, 2021 (GMT)

Hi there,
My Purge Valve Solenoid , the one close to the throttle housing, remains closed even when it receives 8-9 volts from the ECU. But when I unplug it and connect it directly to the battery, it opens and closes when I disconnect. Engine coolant temp makes no difference plus there is no fault code but the car is jerking and idling roughly, plus with new battery it turns over once…twice and then starts, fuel consumption is quite bad. I checked the vacuum hoses from the charcoal canister and there are no leaks.
Any ideas?

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Posts: 434
on: February 17, 2021 (GMT)

You didn’t mention Mfg/Model of vehicle you’re working on. And I have WELL LEARNED there are dramatic differences in OBDII PIDs and Sensors between models – even on like Mfgs. But I have done exhaustive research and hacking the EVAP system on my 2004 Ford F150 5.4L 3v. And find it to be far more complex logic (though simple in practice) system. I suspect your vehicle might be very similar in operation – though likely NOT same PIDs. The Dashboard and a CSV type file with the custom PIDs is posted here:

First the Purge Valve Solenoid (Actually called the ‘Electronic Vapor Management Valve’) is opperated by ‘duty cycle’ pulses from zero to 100 percent. That’s why you are reading lower voltage on it (~ 60%)- and why you see it open/close when connected direct to 12v sorce (100% duty cycle). The ECU learns MUCH by gradually modulating this valve open and ‘noting’ JUST when the pressure in the tank begins to decline. It plays with the voltage at that point, to determine if the EVMV leaks or seals properly. If it can’t change Tank pressure at all = gas cap off, etc. It increases to 100% (with Canister vent valve closed) and monitors time for tank pressure to decay. Determines gross leak, or small leak by time for decay. When it opens Canister Vent Valve, with EVMV open, it can determine how much fresh air passes through the Canister or if Canister Valve isn’t working right – OR other trouble codes.

I suspect some of this would apply to non-Ford vehicles also, although it is doubtful many of my PIDs would match other vehicles. Hope this gives some direction.



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