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Hello. I ran the Evap System Test which has two parts to it. Drawing vacuum and then holding it when sealed. It failed the first part immediately in which the FTP sensor voltage wasn't dropping fast enough from 2.8 to 2.4 volts. Smoke test it and found the fuel filler neck was leaking around the cap. Noticed the neck below the cap was rusted out so I changed it. Smoked it again and no smoke visible this time I even checked under the car from back to front. Purge and vent solenoids shows good sealing. Ran the Evap System Test again and the FTP sensor was showing a faster decline in voltage from 2.8 to 1.8 volts. Drawing vacuum passed but the holding vacuum seal failed. The FTP voltage rose to quickly.
Smoked it again and spent a lot of time inspecting it and find nothing. To make matters worse running the test will sometimes pass. The scan tool allows me to close the vent valve while the car is off but the purge valve can only be controlled while the truck is running. What i did next I'm hoping is a valid test.
Disconnected the hose fitting from the plumbing to the charcoal canister and plugged the plumbing going to the the purge valve.
Disconnected the hose from the intake from the the purge valve and plugged the intake port as to not create a vacuum leak.
Smoke it first with the truck off no visible leaks. Now with the truck running and the purge valve commanded off there is smoke coming from the hose which is telling me the purge is not sealing. Command the purge valve on with scan tool and a lot more smoke is coming out which is to be expected. Command it off and there is still some smoke visible. Turn the truck off and disconnected the harness to the purge turn on the truck...same result.
So the purge valve doesn't leak when the engine is off but leaks when the truck is idling whether the valve is off or the harness is disconnected. The valve is located under the battery located in the front driver's side. Is it the vibration causing this intermittent failure? What else could it be? Maybe i'm missing something the way this valve behaves depending when the truck is off or not. Thanks.
Vw mike wrote: Purge Valve should hold vacuum. Quick easy test is to unplug it and start truck if had vacuum on the tank side it is no good
I could do it that way but it lives under the battery so I have to remove it out of the way. Is it the same thing as applying smoke into it like I mentioned before except I'm not using vacuum?
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