Dave WM

Charcoal Canister

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    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.

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    Interesting. Thanks fof sharing.

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

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    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 by Dave WM

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    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?

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    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 by Dave WM

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    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.

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    Thanks Dave. Good timing... I was in here at the same time you were.

    My read on the spring is the same as yours. Under some circumstances, the vacuum could be the same on both sides of the diaphragm, so in order to get it to open, they need to bias it to the "open" side. And I agree that it would be interesting to see how one of the original carbon cans behaved with a new diaphragm.

    So about your most recent tests... Makes perfect sense that you would run rough (on a hot engine) with a completely disconnected and hanging open purge line. Big vacuum leak. Also agree 100% that the fact that it actually LIKES the additional air on a cold engine is because it's running richer when cold. It's supposed to be richer when cold, but I think they may have gone a little far with that. And there's also a "after start" enrichment that boosts the mixture a little bit more right after you let go of the key. I've measured it and it tapers off over about thirty seconds. So if you had just started the engine, it's even a little richer.

    So on the most recent test above, on the old can, you don't know if the valve was open or not, right? Maybe you could apply your "push down on the cap" test. If it's really that borderline, then the additional thumb pressure might snap it closed?

    I'm thinking that forty years of that spring pushing up against the cap may have bowed the cap up a couple thousandths?

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    I actually tried the pushing down trick not sure if it was working (between the noise of the engine, the balancing of the spare cansister on top of the installed one, and trying to suck on the pipe to activate the purge valve, all the while trying to push down on top of the valve, I just could not be sure if it was working. I could actually hear a click like noise with the new setup as I applied vacuum to the new setup (as well as a slight change in idle). Could not hear anything with the old setup, but that maybe a design issue. The valving while similar its NOT the exact same (I pulled apart a JY valve to investigate).

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    in one of my early "will not start when cold" phases, blaming the CSV  or course.. I installed a 85f thermotime switch. Since its almost always hotter than that it rarely fires (and always starts easy). Well lately its been in the upper 60's and It is firing (I could hear it when I disconnected the solenoid for a fuel pressure test the other day). I plan to test tomorrow with the CSV disconnected, should be in the upper 60's again, will see how starting goes. One thing for sure starting is not always exactly the same. I attribute that to the myriad of mechanical sensors and lack of sophistication of the ECU. It starts and generally easy but just not the exact same every time across different temp ranges. My guess is it does not need the extra fuel for the mild temps, will see tomorrow how it goes.

    As is the vacuum is only good for the idle for a short time (the extra enrichment period you mentioned perhaps).

    Edited by Dave WM

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    Thanks again Dave. I think I'm going to look at those Pathfinder CARB cans next time I'm at the junkyard. My car runs fine, even at cold idle, but if I'm pulling air through that can at idle when I'm not supposed to, I could fix that.

    One thing I've clearly noticed in colder PA is that the mixture is definitely richer as ambient drops. I think they ran the gain on the air temp sensor a little too high. No way I'm going that deep into the ECU to change it, but I think that's the case. I was running a little lean in the summer, but as the temps have dropped, I can smell that I'm richer now. Especially when cold.

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    I think the leakage is pretty minor, but you could just try clamping it off and see if you  can tell any difference at idle. I just pulled the line and held my finger over it, listen to idle after it settles, then reattach and listen again. Takes a couple seconds each time for he engine to recover from the momentary open between switching would tell you if its having any effect, even if the performance effects were nil. OCD strikes again...

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    maybe if I lower the rpm may be able to notice better.... I tend to run a bit high like 900-1000.

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    5 hours ago, Dave WM said:

    I think the leakage is pretty minor

    Agreed. The orifice in the neck of the carbon can is pretty small. Even if my valve never closes, it's not like it creates a big vacuum leak. I bet that over half the 280's out there have other accidental vacuum leaks bigger than that one, Haha!

    So even if mine is open, I probably just tuned it out like an offset. But my idle is lower than yours. I'm running 600-700. Maybe I could hear a difference if I pinched off the purge line.

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    I will drop the rpm and test again later. maybe get it real low like 500 just to see if I can tell a difference (open purge vs closed purge while idling).

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    Quick empirical test... I pinched off my purge line on both a first started cold engine, and a fully warmed up engine and I had no discernible change in my idle quality or speed.

    Doesn't mean much, but I got that. Could mean my valve is closed. Could mean my valve is hanging open, but doesn't make much of a difference either way. Could mean my pinch off was not a complete seal.

    If I get energetic, I'll pull the control line and apply mouth vacuum to it at idle (to force the valve open) and see if I get any discernible change. But I'm running out of Z days now before the weather turns and they salt the roads!

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    think its a non issue, I did more test as well, down to 500 rpm, NO effect and I know the new canister valve is working. So it would seem the minor leakage of a purging system is really not going to be an issue. Not sure why it was deemed it need to open and close the purge valve, seem like it could work just fine perm open.

    I think a dirty EGR is a more likely thing to cause issues with vacuum leaks regarding the emission control system, much larger possible leak and in a dirty environment as well. Just something to keep in mind if so equipped. My take on the canister is its not a issue, at least as long as it has some restriction from the purge line.

    Edited by Dave WM

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    Agreed. I'm assuming that when everything was brand spanking new, tight fitting hoses and gaskets, little blow-by, and all that... Maybe it made enough of a difference that they felt they needed to disable it at idle (and WOT), but these days on worn engines with probable small leaks elsewhere, it's just a tiny unaccounted for offset that doesn't make much difference.

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    Dave, what made you dig into this issue.? Were you experiencing and rough idle post warm up?

    I know a guy that frequents JYs I’m sure he can acquire a few of them for the team.

     I’m headed to one this weekend to pick up a ZX distributor for $30. I’ll be on the look out for a 90’s Pathfinder.

     

    Sent from my iPhone using Tapatalk

     

     

     

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    it was just something that I considered as a possible problem. My idle is less than perfect so always looking for some cause. In this case I think its a red herring, the canister presents enough of a restriction that even at idle the minor leak seem to have no effect. Perhaps as CO mentioned if everything else was perfect it could be noticeable, but in my case its not. Might be something others can look at just for comparison. IF there was a major flaw in the canister I can see how a stuck purge valve could be an issue. Just one more thing to add to the notebook of things to check.

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