Doubt about Vacuum System / Vacuum accumulator

I have read quite a bit about this issue here, but I still have one doubt. The vents for the air blower were not working, so I troubleshooted the system, and found out vacuum wasn't connected to the vacuum system, so I just plugged it to the line that goes to the Vacuum accumulator, and I also threw in a vacuum accumulator since the original one was gone. This helped me to get the vents working, but now, when I drive they often fail again, this is due to a low vacuum caused by driving situations, that's clear for me.

Now, to explain my doubt, I am sure it's not a problem of the line that comes from the engine to the accumulator, as when there's good Vacuum, I can obstruct this line and unplug it from the engine and the vents will work fine for a good while (I could say there are no losses from that line).

So, there are two other things, but I'm not familiar with the vacuum system, so that's why I need some help here.

1. The engine is loosing vacuum somewhere else which doesn't allow the accumulator to work properly, however, the engine runs fine, no vacuum relatet problems as far as I can diagnose.
2. If I turn off my engine, will I still have a good vacuum in the whole system? If that's the case, what's a possible vacuum loss cause that doesn't cause any visible malfunctions?

And, as a last question, if the engine looses vacuum when it's turned off (it will obviously not suck air anymore, but my question is if the system should still have some vacuum), shouldn't I have some kind of one-direction valve that keeps some pressure in the air vents system?

Hope my questions are not too confusing, I'm just not used to test this system.

Regards

There should also be a check valve in the line to the vacuum canister so it can't drop when the engine vacuum drops.

OK, this part is exactly what I was expecting there, hope I can find it here in Mexico, these parts are often rare here as people normall don't care about air vents, window washers and such equipment.

Now, if I understand well, this valve should be on the line of the vacuum canister. I have something like the following right now:

air vents other link that seems to go to the tranny
| |
canister----|----------------|--------engine

I should have it this way as far as I understand:

air vents other link that seems to go to the tranny
| |
canister----|------valve----------|--------engine

Am I right?

Sorry about the terrible diagram, but hope it's understandable.

Regards

canister----|------valve----------|--------engine
Yes Engine---->valve----->canister

The original XJ vacuum canister (accumulator, reservoir, "blimp," or whatever you choose to call it) had a check valve built in to the nipple, and that is probably why you found none in a system that had had it removed.

There should be a check valve between the canister and the engine, so that the canister itself holds vacuum. Without this it will just bleed back into the manifold when engine vacuum goes low. If no vacuum consumers leak, this should allow the canister to hold vacuum for a long time after you shut down, usually enough for a few cycles of the heater controls.

OK, that makes alot of sense. I installed a check valve yesterday, the only one I found, a metallic one, but it internally leaks a little bit, it helped the system somewhat, but it still has that problem. I'll be looking for a better check valve though, however I've not been able to find one which I would trust in.

Regards

Thank you very much for your help. I finally got myself a check valve I could adapt to the system, it now works much better. It still has some vacuum leaks, but at least it holds the vacuum for a few minutes, so I only really have trouble on highway driving, I think this will be solved as soon as I check some of the connections and maybe I'll have to change one more of the hoses.

Regards