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

Posts 1, 2, 3, 4 & 6 are my general information posts, they are all geared towards carbureted rigs, the principles are the same for fuel injected rigs, but the controls will be different.

So yesterday I installed a new Charcoal Canister and did a post in another thread and went on a bit. After I got though with the post I realized I should make a new thread. A couple purposes to that. One would be just to get information out there. It seems like when you look up things like how to set up a charcoal canister on a vehicle that does not have to stock carb it just seems like there is hardly any information out there, but it's really quite simple. Also it can be thread where we just ask general evap questions and hopefully someone will know the answer. And like with the wiper and linkage rebuild threads it can be somewhere we can refer folks to in the future.

I'm going to start with the stock setup and this will be for the 5 or 6 port canisters first found on California emissions trucks, but somewhere in the early 80's they found their way into federal emissions trucks as well. If your truck has two canisters do fret I'll get to that in the end.

So the canister I'm talking about is in the below picture:


You'll notice 5 visible hoses connections. Lets go over what each one of those connections is for.
Starting with the port closest to the bottom of the picture, and on the bottom of the double stack of connections. That connects to a two port PCV valve and is 1/4" line, this is the purge line. So when the canister is commanded to purge, the vapor stored in the charcoal canister is drawn though that line and into the engine where it is burned off as part of the mixture.

Next the line on top of that is labeled control and is 3/16", when vacuum is applied to that connection the canister purges. I'll elaborate on how to set that up for an aftermarket carb, or on a rig that has had all the factory vacuum controls removed, but if you system is intact and functional you'll want to connect that where it came from. Most commonly it'll be a thermostatic vacuum switch on the intake manifold, or something that branches off of it. I'm sorry I can't be more specific on the factory set up for this line but there were a few different ways it was done.

One the middle set of connections on the canister, the one closest to the canister is a 3/8" connection and that is the bowl vent for the carburetor. If your running an aftermarket carburetor it may not have a bowl vent, in that case it is perfectly fine to plug that port and you can see I have done that on mine.

The 3/16" connection above that is manifold vacuum, it can be connected to any manifold vacuum source, either actually on the manifold or on the carburetor it just needs to have vacuum at idle and light throttle.

Next connection up is for the vapor line off the fuel tank. I don't think I need to say anymore but if someone needs me to elaborate let me know.

And then the black knob like looking thing at the top is simply a vent. If your air cleaner housing has a 3/8" connection on the driver side of the housing then you'll want to pop that black knob off. Under that is a 3/8" nipple and you just connect the two together with 3/8" hose.

A couple pictures of the canister installed with general vacuum hose routing.



So far most of that I posted in the other thread so for those of you that saw that your probably wondering what the point is here, well hang on I'm about to get into that in the next post.

Next. If your factory vacuum controls are gone, or you have an aftermarket carburetor or aftermarket carb and intake how do you set up a canister like this. Simple. If there is no bowl vent on the aftermarket carburetor as is the case with my Edelbrock that the PO installed, simply plug that port with a 3/8" vacuum cap on the canister.

Vapor connection remains the same. PCV connection remains the same. And the line to the air cleaner housing is equipped remains the same.

The manifold vacuum source which can literally come off of any vacuum source that has a manifold signal. It is not to sensitive so using a port on the carburetor that is BELOW the throttle plates is just fine.

And then there is the connection marked control. I described how it would have gone to a themostatic vacuum switch from the factory in the first post. If for some reason you need to enliminate the thermostatic switch, such as it's broken and you can't locate a replacement, or you don't want to see it on your intake manifold you can just connect that line to any ported vacuum source. The biggest difference is that the canister will purge anytime the engine is above idle at light throttle, so even when cold. I doubt anyone would have a run ability from connection the control directly to ported, but because the engine is not warmed up and the catalytic converter if equipped is not warmed up there will be a slight increase in emissions during that time.

Next post I will talk about 2 canister systems.

So some trucks have 2 canisters, and if I'm frank I'm not totally sure why some rigs got two other than single tank trucks never had two canisters and two tank trucks sometimes had two canisters. I know California emissions trucks got them first and two tank trucks got them, and some federal emission two tank trucks had them, but I'm not sure if all two tank federal emissions trucks had them when when we were hitting the end of the carburetor and square body days. Regardless there certainly were enough trucks made to make it worth while to talk about.

So they were set up so one canister handled each tank. The main tank had all vacuum hoses connected to it and the secondary tank was teed off of those lines.

Personally if I had a two canister truck, I'd probably keep it like that, but if I had a two canister truck and someone removed most of it and I wanted to reinstall I'd probably just go with a single canister. So for me with my truck, it came factory with only a single tank. Given that it's a 1984 it's a 305 and has all the other emissions equipment, it's probably likely that if it had come from the factory with two tanks, it probably would have had two canisters. When I added the second tank, I simply teed into the existing vapor line and connected the line from the new tank into it, so the single canister could handle both. I figured there were many early year factory dual tank trucks that ran just one canister, it would be fine and it has been.

Ok now I should talk about 3 connection canisters I suppose. The three connection canister can be setup as a three connection or two connection.

Here is a kind of poor picture of a three line canister, sorry I don't have one handy to snap a pic of.



Basic function is the same collects vapor off the fuel tank(s) and burns it off. Setup for a three line is simple and it doesn't matter if the truck has the factory carb and intake or aftermarket equipment.

Starting from the tall port closest to the top of the picture that connection is labeled purge, and it is simply connected to any ported vacuum source, in that setup it simply purges though the ported vacuum. It's not really the best way to setup a canister, but it is the simplest. or it can be connected to an outside control unit.

An outside control unit would consist of a line that runs to the PCV and another to a ported source, with the last line on the controller connecting to the purge connection on the canister. Basically a vacuum control unit and a three line canister function the same as the 5 or 6 line canister it just has external controls rather than internal controls. A guy can put a three connection vacuum canister in a 5 o 6 line truck and using a vacuum control unit have the identical function.

Next port the short one in the middle is where the vapor line from the fuel tank(s) connect.

And the last port in the picture it is plugged off that connects to the bowl vent in the carburetor.

Next and last post in the initial informational will be part numbers.

I think the later 2 cannister trucks were mostly 86, at least in states other than Cal.
They were also equipped with dual air pump systems and stainless exhaust manifolds. Not the friendliest engine compartment to perform repairs.

Part numbers.

So I want to preface this by saying your old canister will have numbers printed on the top of it near where the vacuum connections are. Try to get a canister using those numbers first. If you can't read the numbers, your canister is gone or your canister is out of production use the closest one in the below list.

PN#s are for carbureted engines, but there is no reason they can't be used on an injected rig if they have the correct connections / ports.

3 port canister (can be setup as 2) ACDelco PN#215-153 Standard Motor Products PN#CP1022

5 port canister (can be setup as 6) GM PN#17064627DS NAPA PN#CRB 229805

The ports are getting hard to find but using the GM PN you maybe able to find new old stock which is what I did.

I will see if I can locate the PN for the vacuum control unit I mention in post #4 and will add that in later.

fast 99 said:

I think the later 2 cannister trucks were mostly 86, at least in states other than Cal.
They were also equipped with dual air pump systems and stainless exhaust manifolds. Not the friendliest engine compartment to perform repairs.

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You maybe completely right about that. I just remember them being around but not the specifics as it's been sometime since I've seen one.

oldretiredafguy said:

I ordered one of the canisters, but is not the same PN, nor the correct number of ports that most of my trucks use. Is yours (or mine before I send it back) strictly for carb equipped vehicles 1986 and earlier? Most of my trucks are 1988 and on, all with TBI.

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A lot more general info in this thread, but it's all written with the carbed trucks in mind and the PN#s in post 6 are for carbed rigs. but could be used on an injected rig as well. I'll edit the initial post to mention that.

If you send me the PN# for the part you have I can look it up at work tomorrow and tell you what it is suppose to fit. If you post the year of the truck your trying to replace and the number of ports you need I get you a PN# that will work. A LOT of the canisters have been discontinued over the years, but there are units that will work, but may not be identical.

Thanks for this infos.

Rusty Nail said:

Thanks for this infos.

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Thanks for the feedback. I've done a couple write ups like this and often afterwards it's crickets, so I have no idea if people are making use of them. Appreciate you saying something!

Figures..

Dude I just bought this charcoal canister out of an 85 G10 VAN with intention of replacing the blank spot and plugged hoses in my 88 Blazer.

I figure the entire front clip is 91 suburban but no canister was present at purchase. Air cleaner / diagram is also 91 suburban.
Sometimes the truck "chugs" a bit after letting off the throttle and I figure that's why and im pretty sure the tstat is open when it does. Not all the time, but the chugging is fairly predictable.
ESPECIALLY after a hard run or exiting the highway... Sounds like it wants to die but it doesn't...powers through...dumps the gas out the pipes...gotta be bogged down with unburnt fuel that cant escape I reckon. Sounds like wasted money to me!

I completely expect addition of this $25 scrap yard part to improve the fuel mileage.
The truck idles a ton and I know im wasting money because some monkey took it off. Three years later? Undoing P.O. bs continues. Still trying to restore these systems to their original function, "like the General built it".
I would replace the smogpump in a heartbeat.
You shouldn't take these out... I add them.
You shouldn't take these out!

It aint there for no reason and they are kind of hard to find.




Thanks again - will advise.

I just saw your post and also want to thank you for taking the time to put together an excellent article.

Rest assured, your write ups are appreciated by a majority whether you got feedback or not. This write up is particularly interesting for me, since I'm sure the canisters on my rig are shot.

Thanks for taking the time to write these things up.

@texasmike @Radiohead Thank you guys I really appreciate the comments! Seemed like there was a real lack of info on the canister setup and I'm glad folks are finding this write up useful!

I need to read through it when I get a few minutes. Been considering changing mine since it's 41 years old