Removing the evap canister (Page 2/4)
trotterlg AUG 11, 05:03 PM
I have looked at all the diagrams, they show the small two hoses going to the TBI. I am thinking that one is the vent line and the other some how controls the venting? Any one know which is which? Wlould pulling vacuum on one open the vent on the canister for the other line? Larry
Blacktree AUG 11, 05:58 PM
One line goes to ported vacuum, and the other goes to manifold vacuum. The ported vacuum line opens the valve in the canister, allowing manifold vacuum to pull the fumes into the intake. If I remember correctly, the very top one (which should be the smaller of the two) is the ported vacuum line. You can verify this by tracing the line back to the ported vacuum nipple on the bottom of the throttle body.
trotterlg AUG 11, 07:11 PM
I see 4 choices, now to tell what is "ported"
theogre AUG 11, 08:52 PM
Port will pull a vacuum when throttle is open. Just use a vac gauge. Likely 2 on top but you need a gauge to test because internal plumbing...

In some text...
top/control to port vac
bottom/vent to manifold vac

For reasons only GM knows... they run "backward" on many cars, including Fiero. Maybe vent port flows too much air when connected to manifold vac.
Proof? In some/all Fiero, Top port on Evap also used by Cruise Control. CC needs Manifold vac to work.

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trotterlg AUG 11, 10:05 PM
OK, so the top smaller fitting goes to constant vacuum and the larger bottom goes to the "ported" fitting? Larry
Dennis LaGrua AUG 11, 10:17 PM
No charcoal filter here. I just plumbed the gas tank vent tube to the air filter box. Haven't experienced any ill effects in three years

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
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DimeMachine AUG 12, 10:10 AM
I would keep the evap. If you vent it, it will allow fumes out in the day as it warms, and it will draw in air at night as it cools. Ethanol attracts moisture and so having it vented will increase corrosion in your fuel system by the additional water that will get in there. Plus there is not HP to be gained by deleting it.

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84 NB, 3800SC, E-85, VS Cam, 3.0 Pulley, 4T65E-HD, HP Tuners, AEM Wideband, Regal GS Gauges, S-10 Brake Booster. 1/4 mile -12.05 at 111.7mph

fierosound AUG 12, 11:36 AM

quote
Originally posted by trotterlg:

Don't need it for emissions, What did old cars do before they had them?



Usually stunk up the garage with evaporating gas fumes.



quote
Originally posted by trotterlg:

I see 4 choices, now to tell what is "ported"



Do you have your carb installation sheet/manual??
It will point them out - better than us guessing for you.

[This message has been edited by fierosound (edited 08-12-2013).]

Blacktree AUG 12, 08:28 PM

quote
Originally posted by trotterlg:

OK, so the top smaller fitting goes to constant vacuum and the larger bottom goes to the "ported" fitting? Larry


If you're talking about the fittings on the charcoal canister, then you have it backward.
trotterlg AUG 12, 08:39 PM
Guess I am really confused now.
quote
For reasons only GM knows... they run "backward" on many cars, including Fiero. Maybe vent port flows too much air when connected to manifold vac.
Proof? In some/all Fiero, Top port on Evap also used by Cruise Control. CC needs Manifold vac to work.



So which hose goes to which vacuum? Larry