Charcoal / vapor / evap canister, how it should be set up and other information

[SquareRoot]

The new stuff is also 3 port. I just had to replace the one in my 2011 Suburban because it was clicking off the pump every time I tried to fill the tank. The new vehicles have an entirely sealed system with the canister mounted above the fuel tank right next to it in the back of the vehicle. One line goes straight to a vent port on top of the tank. Second line runs to a computer controlled "purge" solenoid mounted on the intake manifold, and the third port runs to a computer controlled "vent" solenoid bolted to the crossmember right above the rear axle. The vent solenoid then has a hose that runs all the way up to a filter that mounts to the top of the fuel tank fill point plastic. The caps are non-vented and the purge and vent solenoids are activated by the computer based on driving state and fuel tank pressure sensor readings.

Sounds overly complicated. Meanwhile the EPA is spending millions on how to deal with cows farts that's contributing to global warming. The world has gone mad!

 

[SirRobyn0]

Thanks @SquareRoot As for the canister being ruined by fuel getting into them yup I can confirm that is true, but also kind of depends on how bad and when. For example if you fill up both your tanks it's cool out and take it for a drive on a hot ass day, it's likely as you'll get a little raw gas into the canister, but because the engine is running and the canister is purging it's fine. Same thing if you top the crap out of your tanks one time and get a little raw gas in while it's running it'll be ok most times. What kills canisters is guys that top off the crap out of their tank every time they fill it or somehow fuel fuel gets in there with the engine off. So most commonly it's not one occurrence of over filling the tank it's doing it repeatedly.

@Bextreme04 I know the system you are talking about. It gets even better with some of the newer rigs that have leak detection pumps. The PCM will command the purge valve shut, and kick the LD pump on to basically perform a fuel vapor system integrity test. The tiniest leak will set a code and can be hours of fun to track down!

 

[Rusty Nail]

That is fascinating... you'd have to really like fuel vapor...haahaa. Glad you topped this thread

pesky vapor always causin trouble

 

[DoubleDingo]

That is fascinating... you'd have to really like fuel vapor...haahaa. Glad you topped this thread

pesky vapor always causin trouble

As bad as vacuum leaks

 

[73fleetsideABQ]

Thank you for posting this information, it's extremely helpful. I have a dual tank setup and tank are not vented or have vapor lines. Vented gas caps are installed but they simply allow air into the tank when pulling fuel to avoid creating a vacuum in the tank. The tanks build up a ton of pressure, especially on hot days. Question: Is it possible for high gas tank pressure to push too much fuel through the mechanical fuel pump at idle? If so, then we might see carb flooded at low rpm/idle, which would be dependent on outside temp. Hard to set idle circuit with variable fuel supply. Do you think this is a realistic symptom of not controlling tank pressure? Might be a good reason to install vapor/vent system.

 

[SirRobyn0]

Thank you for posting this information, it's extremely helpful. I have a dual tank setup and tank are not vented or have vapor lines. Vented gas caps are installed but they simply allow air into the tank when pulling fuel to avoid creating a vacuum in the tank. The tanks build up a ton of pressure, especially on hot days. Question: Is it possible for high gas tank pressure to push too much fuel through the mechanical fuel pump at idle? If so, then we might see carb flooded at low rpm/idle, which would be dependent on outside temp. Hard to set idle circuit with variable fuel supply. Do you think this is a realistic symptom of not controlling tank pressure? Might be a good reason to install vapor/vent system.

Yes it's possible for fuel tank pressure to push fuel into the carb. Theoretically it could push past the needle and seat if the pressure is high enough. If that's the case it would probably flood out like crazy, and be very hard to start hot. Likely you'd get a fuel smell too. Of course percolation and vapor lock can cause problems as well. if it's a single line truck then those could be a concern.

Your vented caps should both let air in and vapor out. You still shouldn't build pressure with those caps.

If you were so inclined to add a vapor recovery system to the truck the biggest challenge would be that you'd need to replace the sending units with one that have a vapor line port.

 

[73fleetsideABQ]

Thanks for your thoughts. Yeah, probably only something we would see at idle/low rpm when fuel demand is low. Yeah, when I took apart truck to paint and bed was off, I put on new tanks and single line fuel sending units since PO removed lines and vapor recovery system. Kicking myself a bit for not doing right, back to original when the bed was off. Oh well.

That's in interesting point about gas caps. My understanding is that Stant gas caps for 73 chevy are unidirectional and unseats to allows air into tank only to avoid creating a vacuum. Only 2 options for 73 chevy cap, with our without EES. Here is photo of cap with EES:

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The cap even tells you to be careful due to pressure. This is probably the reason folks drill holes in caps, to vent them. There seems to be a lot of confusion regarding gas caps and vented or non-venting and direction. In any case, that topic is for a different post (probably hundreds of posts about caps).

The other question is about a 3-port canister connected to ported vacuum. I just don't understand how the vacuum control valve helps the situation. The original post discussed connecting 3-port canister to ported vacuum but that this was not the best way to connect and an outside control unit was recommended. A vacuum control valve will be connected to PCV (full manifold) and ported vacuum but not sure how that benefits the purge. Any thoughts?? I probably just need to look up how a vacuum control valve operates. Is it just better to send vapor to manifold instead of ported vacuum?

 

[SirRobyn0]

@Reed Selwyn About your canister question. Think of it like this. A 3 line with an external controller basically makes it operate like the 5 / 6 port canisters.

So with the three port the line connected to the ported vacuum source also doubles as the purge line. So when you step on the gas enough the ported vacuum connection gets vacuum and it sucks vapor though that line. In the 5 / 6 port canisters there is a purge line that connects to a double ported PCV valve, so the control line is connected to a ported source and when it gets vacuum it opens a valve in the canister and the canister purges though the purge hose connected to the PCV. In that way it dumped into the manifold though the PCV line rather than the ported line.

You'd be best to either do the simple version of the 3 line without an external controller, or just use the 5 / 6 port canister, and plug off any connections you don't want to use. An external controller has that valve built into it, rather than the valve so it effectively works like the 5 / 6 line. Chrysler was big on external controllers at one time.

You are probably right about the caps, I always assumed they breathed in both directions.

 

[73fleetsideABQ]

Ah, thx for the explanation. Seems like a simple solution with a 3-port canister and external vacuum control valve. Time to drop the tanks and do it right!! Anyone know where I can find an original type canister bracket?

 

[SirRobyn0]

Ah, thx for the explanation. Seems like a simple solution with a 3-port canister and external vacuum control valve. Time to drop the tanks and do it right!! Anyone know where I can find an original type canister bracket?

Now there's a question I can't answer, but I'd check LMC and classic industries. If you just want the canister to stay in place and don't care if it's the correct bracket, you could make a base from a flat piece of metal, and a narrow piece going up and down and a large screw clamp. Would be really quick and easy to make with a drill press and welder. Heck, you could probably skip all that and just screw clamp it to the inner fender or core support. All depends on what you want I suppose.

 

[75gmck25]

I assume your ‘73 may have used a purge system like my ‘75 with 3 port sending units. The vacuum canister does not have an separate purge valve, but my original Quadrajet has a dedicated port for a canister purge line. I don’t know what throttle position or condition opens that port on the carburetor.

 

[SirRobyn0]

I assume your ‘73 may have used a purge system like my ‘75 with 3 port sending units. The vacuum canister does not have an separate purge valve, but my original Quadrajet has a dedicated port for a canister purge line. I don’t know what throttle position or condition opens that port on the carburetor.

It is technically a ported source, but I think they call it timed vacuum because it's "timed" for whenever they wanted it to purge.

 

[73fleetsideABQ]

Yes agree, timed is just ported vacuum above the throttle blades. It makes sense to open the valve based on timed vacuum so that you don't send vapor to carb at idle, which would make setting idle air/fuel mixture a bit challenging. Makes sense to purge vapor to full manifold vacuum as soon as timed vacuum is enough to open valve, which is why it might be good to add external vacuum control valve (or 5 or 6 port canister). Thanks for the idea on just making a bracket, seems straightforward.

Thinking a bit more about gas caps, there are 2 caps available for 73 chevy, either with EES or without EES. I asked LMC if they knew the difference between the two caps. Here are the photos they sent me for Fleetside:
1) With EES (pn:32-4128)

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2) without EES (pn: 32-4122)

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I realized that I have both caps at home and I decided to do a quick breathalyzer test (after a nice dram of whiskey of course). Cap with EES (top photo) would not move air in while sucking or allow air out while blowing. Cap without EES (bottom photo) would allow air in but not out. I guess it might be important to some of us adding evap system to truck.

 

[SirRobyn0]

@Reed Selwyn The only thing I have to add on ported and timed vacuum thing. Is think about this. Depending on how close or further up from the throttle plate the port is will change how soon or late the port sees vacuum. For example ported vacuum on a Holley might not occur at the same time it does on an Edelbrock. I think but to not know that on the Q-jet it is called "timed" vacuum because it was designed to receive vacuum at a certain time. I don't think this matters in the least for a evap system to function, it's just something interesting to think about IMO. As long as the control vacuum hose on the 5 / 6 port canister or purge on the 3 port sees vacuum above idle speed it'll work fine.

 

[73fleetsideABQ]

Howdy. Just for clarification, for the external vacuum purge valve shown below (Amazon ACDelco Professional 214-2294 Vapor Canister Purge Valve), the small outlet is to ported vacuum (carb), the large outlet underneath the small outlet is to PCV/manifold vacuum, and the single outlet on the opposite side is to purge of canister??

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