Vacuum Canister Question

Kim Dawson

CJ-8 Member
CJ-8.com Member
City
Molalla
State
Or
#1
From left to right, one, two, three, four. One is plugged off on two of my CJs. Two goes to the roll-over valve. Three to vacuum at the carb. And four to some vacuum switch near the carb. Where is one supposed to go? And four goes in as far as the raised ring and stops. Is there something inside that mores to open it up or is something not right with this canister?
 

Attachments

Hoover

CJ-8 Member
LIFETIME
City
Livingston
State
AL
#3
It appears the signal/purge nipple is broken on the canister in your image (number 4, far right) - the ported vacuum opens a valve in the canister to allow the accumulated fuel vapors (from the tank, carb bowl) to be evacuated through the manifold vacuum and combusted. Here's an image I swiped off JF some time back when I was trying to make sense of that system.

1599049755951.png
 

Kim Dawson

CJ-8 Member
CJ-8.com Member
City
Molalla
State
Or
#4
Thanks guys. Looks like for the system to work, it needs that ported vacuum so I'll repair that broken nipple. This will be used with TBI set-up so I'll plug that carb vent nipple. Very helpful picture.
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Biloxi
State
MS
#5
If you have a TBI system, I would NOT use the factory canister :twocents:

Purchase a new TBI canister that has two ports:

1) Port 1 goes to the fuel tank vent line
2) Port 2 goes to the fitting on the TB for "Vapor Purge". This is a low vacuum port made specifically for the canister purge.

Simple, clean set up, compared to the OEM/carb canister :twocents:

Post #538, what I used/installed on my now sold Tan Scrambler that had a TBI 350 (have used the same on 258's with TBI):

https://www.cj-8.com/threads/spankrjs-1984-long-term-project.32726/page-27
 

ag4ever

Average Nut
LIFETIME
CJ-8.com Member
City
Richmond
State
TX
#8
I don’t recommend the DeLorean version. I bought one, and it leaked vacuum on day 1. My original canister was in better shape.
 

Kim Dawson

CJ-8 Member
CJ-8.com Member
City
Molalla
State
Or
#9
Went to Napa today. They would have to order the canister and it would be $150 to get it. I like the simplicity of it. Considering using the Jeep canister. Repaired the nipple today. This is going on a Scrambler with a 304 with TBI and no PCV stuff. Can I use the two center ports like Spanks did with the GM canister and cap the other two? Or do I need to use the number four port?
 

Hoover

CJ-8 Member
LIFETIME
City
Livingston
State
AL
#11
The number four port is what operates the valve to enable all the collected fumes in the canister to be evacuated through the manifold vacuum port (#3). Without it, none of the ‘fumes’ would be combusted. Given that it (#4) originally was signaled by vac from a ported source, that meant that the canister fumes were only combusted once the engine goes above idle.

In short, the 4-post canister wouldn’t function without three and four hooked up correctly.

At least as I understand it’s function.

Hoov
 

Hoover

CJ-8 Member
LIFETIME
City
Livingston
State
AL
#13
In a carbureted situation, #3 to the manifold vac source, and #4 to the ported vac source. In a TBI system, I have no idea. I’m hoping to learn a few things here along with everyone else!
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#14
In a carbureted situation, #3 to the manifold vac source, and #4 to the ported vac source.
Same. You still have a manifold source and ported source with a tbi. Manifold is below the throttle plate, ported comes from the CTO valve or similar. It's been a while since I've ran the tbi, but I used an OEM canister with it and I think that's how it works.
Spanks idea sounds easier, and I did have a yj canister on the shelf for that purpose IIRC.
 

Hoover

CJ-8 Member
LIFETIME
City
Livingston
State
AL
#15
So, everything would stay the same on the canister with the exception of the fuel bowl inlet (alleviated with the TBI and capped)? And theoretically the canister would do its job?

Thanks for the lesson, WH- :)

Hoov
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#16
Yep, all but the fuel bowl vent. I don't think it's exactly required with a tbi, but why not try to hook things up like they should be if you've got all the pieces available, especially if you can scavenge a bit of fuel vapor and keep the fumes down in the garage.
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Biloxi
State
MS
#17
Went to Napa today. They would have to order the canister and it would be $150 to get it. I like the simplicity of it. Considering using the Jeep canister. Repaired the nipple today. This is going on a Scrambler with a 304 with TBI and no PCV stuff. Can I use the two center ports like Spanks did with the GM canister and cap the other two? Or do I need to use the number four port?
Ouch, I think I paid $70 for a new canister, BUT that was like 6 years ago :eek:

You can NOT use the stock canister like the TBI canister.

The TBI canister is made in a way that it works with a constant low pressure vacuum on it from the Throttle Body whenever the engine is running. It is a very LOW vacuum source, NOT high like manifold/ported vacuum.

The OEM canister has manifold vacuum applied to it all the time, BUT a ported "purge vacuum signal" is required to open the valve to allow the manifold to suck out the fumes.

The beauty of the canister I used is it's simplicity. Other TBI application are more complicated with the vapor canister. Some will have "purge solenoids" controlled by the ECM to only allow purge when the computer determines. I have yet to see an aftermarket TBI system/harness/ECM that will support the later model ECM controlled purge.

The OEM system I mimicked worked perfect, I never had any driveability issues related to the canister purge, even when the engine was cold.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#18
You can NOT use the stock canister like the TBI canister.

The TBI canister is made in a way that it works with a constant low pressure vacuum on it from the Throttle Body whenever the engine is running. It is a very LOW vacuum source, NOT high like manifold/ported vacuum.

The OEM canister has manifold vacuum applied to it all the time, BUT a ported "purge vacuum signal" is required to open the valve to allow the manifold to suck out the fumes.
I'm confused - the OEM canister can handle a high ported pressure vacuum, so why wouldn't you be able to continue using a high ported pressure vacuum with it, from the temperature switch or whatever that multi-ported doohickey is called that's plugged into the intake manifold? Moe as my witness, I had it hooked up just that way with my TBI and it worked just fine.

Are you saying that a canister from a TBI vehicle would not work like the OEM canister for a TBI/4.2 application and I'm just misreading?
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Biloxi
State
MS
#19
You could continue to use the same ported vacuum signal from the intake to the OEM canister to open the purge valve on the OEM canster on a TBI system.

What I am not sure about/can not remember, does the TB have a large fitting to tie the PCV/canister line into? I think so, would have to?


Personally, I try to match systems, i.e. TBI canister hooked to TBI throttle body like OEM. Cleaner and simpler, should not be any "unknowns".

You could probably use the OEM canister with the TBI with correct routing of lines. I just do not trust 30+ year old canisters to maintain vacuum and not cause a "mystery" vacuum leak which can lead to problems, either carburetor or injected. I am using an old canister on my 1985 CJ7 where I am keeping it 100% original emissions/carb/ECM. But, I did check it out to make sure that the purge valve holds vacuum and that the carb is not sucking charcoal out of it :twocents:

On a Jeep I am more concerned about reliability, a new canister/simpler system is the best way forward :shrug:
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#20
What I am not sure about/can not remember, does the TB have a large fitting to tie the PCV/canister line into? I think so, would have to?
For the canister, what I did is ran a T from the PCV to the big port on the canister for manifold, and a line from the temperature switch to the little (signal) port for ported - I think that's more or less like OEM. The TB has all sorts of connections above and below the plate for various uses, and I've forgotten what most of them were for :)

I agree, though, it's a challenge testing the OEM CJ canisters for leaks - especially that purge signal diaphragm, so if there's a way to use new equipment that would be preferable.
 
Top