Carbon Emissions Canister ('75 Eldorado)

[benji808]

Hi all - trying to get some context on the carbon emissions canister. Interested in everyone's thoughts and experiences.

Shop manual says carbon canister filter should be replaced every 30,000 miles...most likely that didn't happen. Does it add any value if functioning or cause any issues if not? Can I just purchase a new filter, or after all this time better to replace the whole unit?

Also, on the replacements I'm finding, like this one: https://www.autozone.com/engine-management/vapor-canister/p/acdelco-vapor-canister-215-153/616178_0_0, the plug arrangement is a little different (two stacked vs three separate on my OEM). Does that matter?

[benji808]

Update here: I bought a new canister from Oreilly's. It was about $90, and seems to work great - hose connections were a slightly different layout than OEM, but all 3 were there, and were the correct sizes. Easy enough!

[TJ Hopland]

Did you get the one you linked to above or a different model?

A little later they started adding 'active' controls to the system.  Initially you could see that one of the ports had a little vacuum operated valve on it.  By the 80's they were solenoids that the computer controlled.

My guess was the 3 ports were:

-1 vent line to gas tank for 70's GM usually 5/16"
-2 vent line to the front top of the carb 3/8, thinking this came slightly later than 75, was for sure a thing by 78
-3 purge line which went back to the carb and was what sucked the 'fumes' into the engine to be properly burned.

The 2 line version was around in the early 70's and maybe sooner.   

[benji808]

Yes - got one similar if not identical to the one linked. My original had 3 ports, going the places you mentioned. The new one has the same; the layout difference I referenced appears to just be the physical location of the plugs.

[RyanaHunter]

If the canister isn't functioning properly, it can impact the performance of the engine and the overall emissions system. It's best to have it checked out by a professional to determine if it needs to be replaced or if just the filter will do. 
Regarding the replacement options you're seeing, the plug arrangement being different is something to consider. It might be best to stick with the OEM setup, especially if you're not sure if the new one will work with your '75 Eldorado. Also, check out Carbon Click. They're a pretty cool website that provides information and resources on all things related to carbon emissions and sustainability.

[Chopper1942]

Those old canisters usually didn't cause a lot of problems.  Replacing the filter is usually all they needed.  What caused most of the damage was overfilling the gas tank, tank vent plugged, or bad cap.  Fuel would be pulled into the canister and saturate it.  This could cause the carbon granuals to brake down and be drawn into the engine.  If the canister has 2 ports, the large one should go to the fuel tank and the smaller one to the carb.  Make sure it is connected to ported vacuum.  If connected to manifold vacuum it will purge the canister all the time and cause the engine to be rich at idle. With 3 ports, 1 goes to the tank, another to manifold vacuum at the carb or manifold, and the third to a control device which may be either a vacuum diaphram or electo-mechanical valve.  Some also used a large line that went to the air cleaner so only clean air is drawn into the canister. The canister bottom is sealed and it does not have a replacable filter.

[TJ Hopland]

The 'fix' when you had a damaged canister that was letting crap get sucked into the carb was to install an inline fuel filter in the line to catch the bits. 

I said 'fix' in quotes because obviously the only thing that fixed was stopping the crud, it didn't really fix the actual issues. The reason you would 'fix' it was if you had a visual emissions inspection you could not just disconnect the system.   

[fishnjim]

Part of the lost decade + of EPA mandated emissions controls without much knowledge of how to do that and next model year coming fast.  They kinda felt there way up the food chain, to meet higher and higher stds.  SMOG was a real issue in the day.
One reason I by-pass this era.   Things kind settled down by the '90s and FI & ECMs were perfected.