Charcoal Canister

[Dave WM]

While futzing with my car I decided to check the operation of the carbon canister. The only real function is the vacuum controlled valve the activate the purge cycle (pull vapor from the can to the engine intake vacuum). What I found was the valve would not close in the absence of vacuum at the signal line (ported vacuum small hose). I test it using a hand pump and vigorously pumping. Now maybe in the presence of a constant vacuum source it would "catch", the design of the valve would tend to do this. I could make it catch by simply applying some pressure to the top of the valve, but that was not enough for me. I removed the valve cap, and found a good diaphragm, but it had a shiny spot where is sealed the port inside. Again I don't know just how aggressive the vacuum need to be, so I decided to see if I could find something a bit more positive in action. Trip to the local JY turns up a mid 90's I think, Nissan pathfinder. It had the same size canister and the 3 needed ports, for 5$ cant go wrong. When I got home I found it to work very well, any vacuum is instantly sealed by the valve, until just a light vacuum from the control line is applied. It was about a simple a swap as you could get. Just wanted to share. Oh for fun I did manage to get my OE valve working, I smeared a very thin film of non hardening sealer on the button of the diaphragm that is supposed to seal. Let it set up overnite. Now it works better, several aggressive pumps from the mini vac and it will seal up, and the control line will break the vacuum, but I still think the JY pull works more posistively, both on the seal and the release, so will stick with that on.

[EuroDat]

Interesting. Thanks fof sharing.

Can you post a photo of the new canister set-up?

[Dave WM]

working on video right now, will be up in a few. I guess the only variable could be the amount of restriction in the draw of the vapor out of the canister into the intake manifold. I guess I could so a subjective test to see if I could feel any big difference by must pulling a constant vacuum with my pump and seeing what the readings are. I did that kind of test when checking out a AC evap valve. IF there was a huge difference I suppose it could be noticeable to the engine as a vacuum leak, but even then it would only happen at higher throttle settings. I will give it a drive test to see if I can notice anything different, but I doubt I will.

Edited November 17, 2019 by Dave WM

[Dave WM]

video

 

[AZDatsun]

They are from late 80’s pathfinders
https://www.rockauto.com/en/catalog/nissan,1987,pathfinder,3.0l+v6,1211768,exhaust+&+emission,vapor+canister,5180


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[Dave WM]

hmm guess I should have looked more closely at the year.

[Dave WM]

https://www.partsgeek.com/gbproducts/DC/6747-05178841.html

[AZDatsun]

Ok the 90’s ones are easier to find for sure... good catch!


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[Patcon]

$5 seems like a score!

[Captain Obvious]

Dave, A while ago I was messing with my carbon canister and noticed the exact same operation you described... Able to pull air through the purge line (using lung vacuum) with no vacuum on the control line. My assumption (just like you) was that when there was more vacuum on the purge line (with the engine running), the diaphragm would be pulled down and seal off the purge hole.

You're saying that's not normal? You're saying it SHOULD seal with no vacuum on anything? How can that be with the spring in there pushing the diaphragm away from the sealing seat?

[Dave WM]

I think its pretty close, the spring in conjunction with the tiny bit of lift from the vacuum on the diaphragm uncovers the port, without the spring it would never release (like a counter balance). I think the spring is there to make the purge valve more sensitive to the ported vacuum switch. Of course its just a guess, but as you can see in the video the other canister works very well as far as the ported vacuum controlling the operation of the purge process. And how it holds vacuum with a single pump on purge fitting. That other canister may just function differently. Would be nice to know if a NEW diaphragm installed in the old canister works differently.

Edited November 18, 2019 by Dave WM

[Dave WM]

ok just for fun, after warming up the car, I disconnect the purge line and as expected car runs rough (vacuum leak) Interesting fact, when 1st started, the same vacuum leak allowed the idle to raise quite a bit and still be smooth, so I guess my starting mixture must be a bit rich, maybe more than it needs to be. Anyway back to testing I reconnect the purge line, then activate the purge valve manually again at idle. an almost imperceptible change in idle, so clearly the canister itself must present a substantial restriction in the flow to minimize the effect of the open purge line. I try the same with the old OE canister, this time I note NO change in idle (and it would be hard to tell if the idle was worse than with the newer canister option) when the purge valve is opened manually (it should be close at idle since its operated on ported vacuum). My guess is its always open but as with the later model canister the restriction of air flow must be enough to mask the effects of an open/closed purge line.

Bottom line, unless the canister is compromised to the point of allowing a massive vacuum loss (and I don't know how that would be) the restriction it presents to the intake manifold vacuum is enough that it will have little to no effect on idling. If it is indeed stuck open, then it will function to capture vapors and burn then in the combustion cycle. At this point I am not sure why there needs to be a open and close of the purge valve since my orig thought was to not effect idle adversely from a vacuum leak.