Georgia Fiero Club Forum
All Things Fiero => Tech Tips, Tech Questions => Topic started by: Fierofool on July 02, 2019, 10:27:18 am
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In the July 2019 issue of the Georgia Fiero Newsletter, the fuel system is the feature of an article. While talking with the writer of the article and Editor of the newsletter, I learned that the vapor canister is actually purged by the EGR solenoid. Through all the years, this is something I never realized. For anyone that hasn't converted to the DIS system, take a look at the routing of the vacuum lines coming off the EGR solenoid, leading to the vapor canister.
Now with this revelation, a question comes to mind. When converting to the DIS system, the electro/pneumatic EGR solenoid is eliminated. What happens to those vacuum lines going to the vapor canister? How is the canister now purged?
I'll give this a little while here before asking the question on PFF.
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I never realized this. Never paid attention to it.
I was thinking there was an electrical connector on top of the canister. Maybe the EGR line was just a convenient vacuum source?
(With that said, I just have a hose from my canister to a fitting on the air intake duct. No other vacuum source. Seems to work okay, and haven't blown anything up, yet. :D )
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The purge valve on top of the canister is apparently a one-way valve. It would seem that if there was a constant vacuum on it, as in your case, it might cause a higher idle as if it were a vacuum leak. Maybe the Cadillac engine works differently regarding evap. I wonder if that might be the cause of some of the stock Fiero high idle problems.
I'll need to look at one of my spare evap canisters tonight to see how it works.
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My canister has constant vacuum. It would not be a leak, unless the gas cap is removed, or if there is a hold in the fuel system.
There was already vacuum, and mine is set up to T everything together.
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OK, I've pulled out an evap canister and I've looked at how it's installed on my 86 V6. The canister isn't hooked to any part of the EGR system. The large hose coming off the canister goes to a metal line leading to the fuel tank. That's where the vapors come from. Probably pushed there by pressure in the tank. The other two hoses attach to the metal lines that run across the trunk wall, transition to a double port coupling near the MAP sensor and disappear underneath the upper intake manifold. I have identified their termination as the larger of the two goes to a port on the throttle body. That's the one on the top of the canister valve. The smaller one connects to the nipple above the distributor on the upper intake manifold. These two ports are what control the purge valve.
When the throttle is opened, the vacuum increases at one of the ports and draws the fuel vapors that are stored in the tank, into the intake stream. Most likely, that would be at the throttle body. My theory is that the vacuum on the two hoses are equal at idle or cruise speeds and the purge valve only operates at any time there is acceleration.
So, going DIS/7730 and eliminating the electro/pneumatic EGR system wouldn't affect the evaporative control system.
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Interesting. On page 6C-6 of the '88 Service Manual, it states the following:
Canister Purge Valve and Solenoid
The Electronic Control Module (ECM) controls the vacuum to the canister purge valve. When the computer command control system is in "Open Loop", the solenoid valve is energized and blocks vacuum to the canister purge valve. When the system is in "Closed Loop", the solenoid valve is de-energized and vacuum is supplied to operate the purge valve. This releases the fuel vapors, collected in the canister, into the induction system. (See Section 6E Emission Control System).
If the Canister Purge Valve is faulty, the canister assembly must be replaced.
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There are no electronic connections anywhere on the 86 or 87 vapor canisters. Just 3 rubber hoses connected to it. All the hoses go to non-electric components. Could that be referring to the (87) 88 Duke?
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This is possible.
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There are no electronic connections anywhere on the 86 or 87 vapor canisters. Just 3 rubber hoses connected to it. All the hoses go to non-electric components. Could that be referring to the (87) 88 Duke?
Certainly sound as if this is for a Duke. That is how mine is set up, 3 vacuum hoses and that's it. Also, the EGR on the 88 Duke is not ECM controlled, hence no electronics or solenoid.
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I believe all the Dukes employ a different method for EGR control. I do know that the EGR valve is different from the V6. TopNotch once explained how it worked but I don't remember. The Duke doesn't have an electro/pneumatic EGR solenoid and works solely off the engine.
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There are no electronic connections anywhere on the 86 or 87 vapor canisters. Just 3 rubber hoses connected to it. All the hoses go to non-electric components.
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There's a good chance I was mistaken about my 88 too, then. I was working off of memory. Haven't actually looked at the car in a while.
I seem to remember the large hose to the tank, and then two other vacuum lines. IIRC, one line went to "constant" manifold vacuum, and the other to "ported" vacuum (which only is active "off idle".) My thought was that the vapors were sucked out through the "ported" line. That's the one that I plumbed to the intake duct, instead. I'm not sure of the thought process I was using, but it made sense at the time. :D
Edit - The Duke EGR system is based largely upon sorcery and witchcraft. Or maybe just vacuum and exhaust back-pressure, if you choose to believe the manual. But no solenoid, or other electrical bits.
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My 88 duke has three lines coming from the canister. Two go to the intake manifold, and the third goes down. I'll have to crawl under the car to see where it goes, but I suspect it joins the fuel system somewhere.
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Thanks for the help on this, Fierofool. I'll post the correction soon.
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Pat, the big hose coming off the canister is the one that goes to the tank. There's a one-way valve attached to the bottom of the sending unit flange. That's where the vapors come from.
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You guys are on the right track...
On the standard intake for the v6, the canister is activated via ported vac. The purge is dumped into the intake vac line. Its all vacuum actuated.
Yes, 7730 provides the option of using a solenoid switch to replace the action of the ported vac connection, but is totally unnecessary unless the intake is changed.
The 88 Duke may have the solenoid because it shares a lot with the 7730 platform. Idk.