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Sherman Tank vent to charcoal canister

bsquared

Contributor
Sr. Member
Joined
Dec 4, 2010
Messages
960
Is anyone running the 23 gal Sherman tank w/o venting to a charcoal canister and just using the vent to the filler neck for the tank to breathe? I've got the charcoal canister mounted well above my tank in the engine bay. Also have a catch tank just before the canister and filled it up in no time after filling the gas tank to about 3/4 full.

Took a few turns and next thing I know the engine is bogging from the excess gas being stuffed directly into the upper manifold. My vent out of the canister runs to a vacuum port on the upper manifold. Can't drive it like this, for sure!

I'm running a '96 EFI that has a return, so I don't have another port on the tank to drain the catch tank back to it.

Thanks in advance for your advice. Cheers, B2
 

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Hinmaton

Full Member
Joined
Oct 17, 2017
Messages
590
I’m running a BCB 23 gallon tank (same-ish tank) without a canister. FiTech EFI with return line.
I also have moments of over flow out the vent tube (which I have plumbed beside the full tube).
I put a vent cap doo-dad on top, but it only flows inward. The cap doesn’t really vent, so it was causing all sorts of issues as the pressure was trying to escape. I’m back to just venting to the atmosphere and living with a bit of spill here and there.

Not great, but not too bad either.

Hinmaton



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DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
...My vent out of the canister runs to a vacuum port on the upper manifold.

Didn't look at the pics in detail yet, but are you running a fully controlled purge solenoid on a legit CAN-P (canister purge) circuit from the ECM?
If not, then you can't run any vacuum at all to the evap system. Or it will just do what you are describing.
There is not supposed to be any extended vacuum in the system. Only momentarily to purge the fumes during a very few limited circumstances.

If you're not running a CAN-P system, then you need to disconnect the vent line from full vacuum and plumb it instead into the air filter, or intake tube ahead of the MAF sensor.
It can actually go in the tubing between the MAF and TB I think, and that should run just right too. It just can't be anywhere behind the throttle body where it will see full vacuum.

Paul
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,796
I am pretty sure the vapor canister needs to be vented to the outside of the air cleaner part of your induction. Do not plug it into manifold vacuum.
 

904Bronco

Contributor
Bronco Guru
Joined
Sep 28, 2004
Messages
5,749
Loc.
San Martin, CA
You cannot run full manifold vacuum to the CC. Having that constant source is pulling fuel when the engine is running and the tank is full.

As Paul said Tank purging occurs during cruise speeds - 2000 rpm'ish. (With CAN-P)

There are a number of threads where others have done just as Paul has suggested, using the vacuum of the air being drawn into the engine to purge the CC / Tank, by placing a port on their air inlet tubing before the TB.
 
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