Charcoal Canister Relocation

[wheee!]

I am thinking of relocating a smaller canister (from a Sentra maybe) up to the firewall. I will have a fuel return line after the FPR so that's not a problem...

 

[Captain Obvious]

About the charcoal can... They use a ported vacuum source to actuate the canister purge.

They don't want to pull air through the can at idle, or at WOT as it is essentially a controlled "vacuum leak" and could adversely affect stability at idle and performance at WOT. The only time they purge the can is at light cruise.

So... With all the changes you're making, are you planning to still have access to a suitable ported vacuum source peaking at light cruise?

[wheee!]

:crying:

[wheee!]

As long as it is plumbed the same as the stock can, I thought it would work the same. The can posted above seems to be actuated the same as the stock can...

Bottom line is I want it gone from the front of the engine bay so I can clean up the fuel lines. Venting the gas tank evap line to the filler neck will allow the tank to fill properly but not vent when capped. A relocated evap can down by the fuel pump seems to be another possible solution. Close off the engine side of the evap and vent the tank under the car. Yes, I will be losing some gas vapour that won't be going through the intake but I'm not going to lose sleep over that. Thoughts?

[Captain Obvious]

Sorry, but I'm not sure I'm understanding... You are correct that as long as it's plumbed the same as the stock can, then that Sentra can should work just fine. You need three connections to the carb can. A vapor IN connection, a vapor OUT connection, and a CONTROL signal connection.

The vapor IN connects to the overflow/separator tank thingie inside the right rear quarter panel.
The vapor OUT connects to any constant always present vacuum source like the intake manifold, or the balance tube (if you're running carbs).
The CONTROL signal connects to the ported vacuum signal that is also used to control distributor vacuum advance (high vacuum just above idle and no vacuum at other throttle positions).

If you've got those three connections to it, I don't think the physical location of the can matters.

I was just questioning if you were planning to have access to that ported vacuum signal. I wasn't sure if you were planning to run the original throttle body, or switch to carbs that did not have that signal available.

 

 

[wheee!]

Gotcha. It will have the original throttle body as I don't have plans to install the Megasquirt etc in the car and need to keep engine performance within factory spec.

If there was a way to lose the evap canister in the rear quarter along with moving the charcoal can to the undercarriage, that would be a great solution! Room for a speaker on the passenger side and no more can in the engine compartment. The reason this is important to me at this point of the build is, I want to remove the mounting point in the engine bay before paint and bodywork.....

[Captain Obvious]

Well moving the carbon canister to somewhere else ought to be no problem. I think getting rid of the tank behind that rear quarter panel would be a little more risk. You do not, under any circumstances, want to push liquid gasoline into your carbon canister. My read on that overflow tank behind the quarter panel is that it is the highest highest highest point that liquid could ever ever reach.

And then they pull a line off higher than that for the vapor recovery system.

[wheee!]

I agree. It would just be a "nice" thing to have changed. In the end it will probably remain in the quarter panel.

New cars don't have them though ... do they??? Not to keen on having a vacuum line run the length of the car though too....

[Captain Obvious]

I don't know about new new cars, but they used the same basic concept in the 2000's.

Couple differences though. The cans weren't always round, but were shaped to fit whatever tiny odd shaped space was available, and another difference is that the actuation was usually electrical through the use of a solenoid valve instead of the vacuum driven valve built into the cap on top of the can.

They used the control brain to purge the can under the desired conditions instead of a vacuum signal. And diagnostics were incorporated into the system as well.

[wheee!]

So if I understand correctly.... I can relocate the can under the chassis by the fuel pump IF the vapour tank is kept in place and the vacuum line is still connected to the throttle body. The can will "vent" under cruise and I can dump to atmosphere under the car. So I would need a vacuum line to the back of the car. Basically keep the hard line at the firewall to go back to the can....

[Captain Obvious]

Based on my understanding of the system, I believe you nailed it.

Needing that vacuum line at the back of the car kinda negates some of the advantages of moving the can though, doesn't it?

[wheee!]

Not really I suppose because there is already a hard line there that was going from the vapour can to the charcoal can. I will just route the hard line farther up the firewall to a place where I can run vacuum to the throttle body.