I'm replacing the vapor cannister filter in my '72 LT-1. I also read something about adding charcoal on one of the other forums, but there were no further details. Is the charcoal something I need to add?
Thanks,
Tony
Thanks,
Tony
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Re: vapor cannister - adding charcoal?
The charcoal is never consumed and never "wears out". I'm not familiar with replacing charcoal in the can, and all GM cars used essentially the same can, so there are millions out there in junkyards, and I suppose new replacements are available, too, but it's not a part that would usually every have to be replaced due to functional failure.
Duke -
Re: vapor cannister - adding charcoal?
I believe there was a woven or foam filter of some sort in the bottom of the canister that was replaceable; as Duke said, the activated charcoal adsorbent material is "forever".Comment
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Re: vapor cannister - adding charcoal?
That woven fiber filter is "washable", but I bought a new Purolator brand for my Cosworth Vega at Pep Boys for about a buck and a half a few years ago. It looks just like original and is not visible unless you remove the cannister.
GM probably built about 25 million cars with that same cannister, and they all use the same filter.
The charcoal absorbs HC molecules and then gives them up when the cannister purge valve is opened by manifold vacuum. The port for the purge valve vacuum is above the throttle plate at idle, so purge doesn't occur unless the throttle is somewhat above idle.
Purge draws air through the filter on the bottom of the cannister, and this "ventilation" of the charcoal causes it to give up its absorbed hydrocarbens,which are then consumed by conbustion.
Beginning circa mid-seventies GM also began installing little charcoal cannisters in brake vacuum booster lines to protect the rubber booster parts fron HC attach. It absorbs hydrocarbons that can migrate through the line to the booster, and every time you depress the brakes air flows from the backside of the booster (where there should be a little foam filter) and through the charcoal on its way back to the manifold, so the charcoal gets "purged" everytime you depress the brake pedal.
It's about the size of a GF-90 fuel filter, and it, too, should essentially last "forever".
DukeComment
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Re: vapor cannister - adding charcoal?
So is the charcoal sealed inside the can? I've read somewhere that your supposed to add some charcoal granuals when you replace the filter.Comment
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Re: vapor cannister - adding charcoal?
As far as I know there is no way to non-destructively open the cannister to access the charcoal, and GM service literature does not call for charcoal replacement.
Don't believe everything you read, and always consider the source.
The only maintenance requirement is FILTER change, which should be listed in the mainteance schedule in the owner's packet, and service manuals have details on emission control system inspections and maintenance. For 1976 the recommended cannister filter replacement is every 30K miles.
Whever you run across one of these "someone said..." or "I thought I heard..." always verify it with GM documentation like service manuals.
The world is full of myths and misinformation - like confusing "charcoal replacement" with "charcoal cannister FILTER replacement.
DukeComment
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Re: vapor cannister - adding charcoal?
Old adage, lotsa truth. "Believe nothing you hear and only half what you see".Dick WhittingtonComment
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