Charcoal Canister

[Captain Obvious]

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?

[Dave WM]

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).

[Dave WM]

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 November 18, 2019 by Dave WM

[Captain Obvious]

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.

[Dave WM]

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...

[Dave WM]

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

[Captain Obvious]

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.

[Dave WM]

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).

[Captain Obvious]

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!

[Dave WM]

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 November 20, 2019 by Dave WM

[Captain Obvious]

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.

[Av8ferg]

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.

 

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