I'm helping a friend complete a 4.9L swap that has lingered on for years. I gassed up the car in cool weather and then we hit 90 'F. He had installed an after market lockable gas cap. When I removed the gas cap there was a serious amount of pressure on the tank. I thought I must have plumbed up the EVAP system wrong. But that all checked out. I removed the EVAP canister and tried to blow through it and that was a no go. Bought a used EVAP canister off Ebay (couldn't find an exact match new one) and with that one I can blow through it easily. Cut the old one apart and couldn't find any signs of why it was plugged. Weird!!!

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

there is a "filter" on bottom of the "can" that could be stuffed w/ crap.
The filter is just unwoven floss and easily replace normally but in this case likely plugged the whole bottom of the can.

Water or Liquid Fuel will cause problems too.
The charcoal can "suck" water from bottom w/ crap in/on floss filter and "shield" on the bracket.
Fuel can push up the EVAP Vent line when people "stuff the tank" getting gas.

E2A-->The bottom maybe snapped into the body... If can remove that w/o wrecking then can refill w/ new activated charcoal like from aquarium shops.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 05-04-2023).]

Why buy or bother with used 20+ year fuel Vapor canister when new ones are still available. Also like Orge mentioned above, you can pick up some Acid washed coconut shell granular activated carbon and repack your own. Coconut shell type is great for removing volatile organics. Acid washed is virtually dust free.

https://www.summitracing.com/parts/smp-cp1038

(Google) Alamo (A9231-AL-1) 12x30 Mesh Acid Washed

Spoon
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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

[This message has been edited by Spoon (edited 05-04-2023).]

Note: My post above is for OE Fiero and other "Dumb" units that lets air/fumes flow all the time for port for the tank.
Small ports don't flow to test w/o following "rules."
1 port never flows as it opens a valve for the other small port under vacuum.
Other small port has that valve that's closed w/ engine stopped.

Also... Another version of the Can has different port(s) because the small ports on Fiero can moves to "remote control" in another part. Either a "Dumb" or ECM/PCM remote controlled. Dumb units have same "dome" snap to the bottom like Fiero units. You need the dumb control and can to hopefully work in normal Fiero.

quote Originally posted by Spoon: Why buy or bother with used 20+ year fuel Vapor canister when new ones are still available.

Was available and fairly cheap but Not Fiero and many other old cars now.
Most stopped carrying that part years ago because whoever made it stopped and just run out of inventory. Might find NOS EVAP "cans" on E-bay or RA at different times.

⚠️ Warning: Many say the "can" but only have the Filter for the bottom and cost a lot at "GM Parts" online like ~ $20 to $30 just for the bottom filter.
Might find Fram bottom filter but I think Fram no longer make them.

The 4.9L carbon canister is a sealed unit. The vapors enter the top, go to the bottom through a tube and percolate up through the carbon and out a vent at the top. The only way to replace anything is to cut it apart and then glue it back together. The solenoid valve that controls the purge is integral to the carbon canister.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

[This message has been edited by sanderson231 (edited 05-04-2023).]

quote Originally posted by Spoon: Why buy or bother with used 20+ year fuel Vapor canister when new ones are still available. Also like Orge mentioned above, you can pick up some Acid washed coconut shell granular activated carbon and repack your own. Coconut shell type is great for removing volatile organics. Acid washed is virtually dust free. https://www.summitracing.com/parts/smp-cp1038 (Google) Alamo (A9231-AL-1) 12x30 Mesh Acid Washed Spoon

It's wild... you posted this just last week, and already it's sold out. I can't find them anywhere online. Looks like they're totally sold out everywhere. There are some other ones, but they don't have the vacuum operated valve.

quote by 82-T/A [At Work] It's wild... you posted this just last week, and already it's sold out. I can't find them anywhere online.

If you really need a new vapor canister with the vacuum valve:

GM 17075840 / AC Delco 215-35 (SMP CP1021) WITHOUT the bottom
$190 on eBay (OE Bulk Packed Vapor Canister 17075840)