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Old 06-23-2020, 11:00 AM   #10
Who's askin'?
maytag's Avatar
Join Date: Mar 2018
Location: Utah
Posts: 2,446
Originally Posted by JFP in PA View Post
I really is not important if the valve faces pressure or vacuum, only that it works when power is applied, and that when it is open, there is flow through it.

The EVAP system is supposed to absorb (actually adsorb, but that is another science lesson) hydrocarbon vapor accumulating in the fuel tank onto the activated charcoal in the cannister; under the correct operating conditions (warm engine, high intake system vacuum), the purge line opens, sweeping air thru the cannister media and pulling the hydrocarbons into the intake to be burned rather than released to the atmosphere as they were with the vents on older fuel systems. The the lines need to be clear, and the valves have to open on command from the DME to get rid of the vapors.

aaaahhhhhh this is good stuff, JFP! I understood, of course, the 100k foot view of what it is supposed to do, but not the mechanics of it.

So here's where I'm at then: Cold engine, I have voltage at the purge valve. didn't bother to pull it out yet to check it, because it's a PITA to get to, and I didn't have any way of knowing if voltage should be opening or closing it.

So SHOULD I have voltage when the engine is cold? And if the answer is yes, then I can assume the valve is normally-open, and the voltage holds it closed. Yes?

OR - do I have a problem in the control someplace, indicated by the presence of voltage when cold?
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