I'm planning on isolating the canister so I'm not trying to apply vacuum to it. I'm going to disconnect the lines. The canister is a variable I want to eliminate from my testing. I'm currently focused on just testing the lines. When I did the EVAP purge line I had it disconnected from the canister with a hand pump on one end and a vacuum gauge on the other end so I could compare the vacuum change on each end of the line. Both ends lost vacuum at the same rate.

Without a smoke machine it seems that the only way to diagnose the problem is to individually test the components. Based on what I've tested so far my suspicion is on the purge line from the engine. That will be a challenging line to repair or replace.

 

I'm having the same issue and came here to find the answers. I have the solenoid valve off the car. It flows freely. I did your test and applied battery power and the valve actuated, but is sealed with no flow with the power applied. What might be the reason for that?

 

Your solenoid is working correctly. In his earlier post the Cap'n had it reversed. I've found out the vent solenoid is normally open allowing the EVAP system to vent to the atmosphere. During the test cycle while driving the solenoid closes which seals the EVAP system. The test cycle is also when the purge solenoid on the intake manifold applies vacuum to the system. If there's a slight loss of vacuum during the test the P0442 is set.

Here's a quick list of what I've done diagnostically so far: replaced gas cap, removed filler neck assembly and tested it, removed purge line at both ends and tested it, removed vent solenoid and tested it. The gas cap didn't solve the problem. The filler neck held both vacuum and pressure when removed from the vehicle. The vent solenoid worked properly. There was a slight vacuum leak on the purge line. Before I declare that the winner I want to test the EVAP lines going from the tank to the canister. I was reinstalling the filler neck when I smacked my hand pretty good so I don't know when I'll finish my testing.

When I complete testing I'll post back with my findings. Good luck with your truck.

 

I got back to work on the Jimmy again today. I reinstalled the fuel filler neck. Everything is sealed up tight with new 2" Gates fuel hose and hose clamps. I also pulled the canister out and a little bit of gas came out of the tank port, maybe a teaspoon at most. I couldn't seem to get any more gas out of it. The canister held vacuum just fine with the vent port blocked off.

I didn't feel like dropping the tank to get access to block off the tank EVAP lines at the tank end so I didn't test them as thoroughly as I probably should have. Instead, because of the vacuum loss on the purge line going to the engine I retested that line. I first checked the vacuum port on the purge solenoid on the intake manifold. It held vacuum. That ruled out the solenoid as a source of the problem. Next I reconnected the purge line to the solenoid and tested the line from the back of the truck. It still had the slow vacuum leak.

Based on that test I'm going to come up with some kind of replacement for the purge line. I'm open to your suggestions. It's a long run to make with vacuum hose. I'm considering just going straight from the nipple on the purge solenoid directly back to the purge port on the canister.

Thoughts?

 

I would not use vacuum hose for the purge line because the gas vapors will possibly degrade it. I tore out the original rusty steel lines used some 1/4" rubber fuel line all the way back to the canister. I think it was about 9 or 10 foot in all and it is easy to route.