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Registered
Join Date: Mar 2008
Posts: 20
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charcoal cannister
Where does the vacuum hose from the charcoal cannister-purge valve connect to the throttle body? Or is it spliced into a line for a different component? I don't see it's installation on any of my vacuum schematics.
BTW, I have only one vac outlet off my distributor. I don't know if this would make a difference. '79 928 |
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09-07-2008, 03:25 AM
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Network Native
Join Date: Jan 2007
Location: SoCal
Posts: 10,349
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Vacuum comes from the intake manifold and the throttle body. I'll try and link to a longer explanation later.
Canister vent goes to a on/off vacuum controlled valve (looks kind of like the one for the heater) to a Y, which I think has one end on the U tube breather below the throttle body and the other goes to the AC aux air valve and up to the intake body. ******************** Link to long thread with more detail on vacuum lines etc. OB vacuum lines Last edited by Danglerb; 09-08-2008 at 10:13 AM.. |
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09-07-2008, 02:18 PM
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Old 928 Guy
Join Date: Oct 2005
Location: Maryland
Posts: 408
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based on my research for my '81, i think there were different schemes used in the earlier cars..(I've even seen diagram where the carbon canister has 3 ports instead of 2)
not sure about your '79, but i do have this diagram for '80 and '81 (which are different). Basically on these the "Y" fitting larger hoses go to the canister and the check valve (ultimately to the "U" part of the intake manifold underneath the throttle (but you probably have K-jet and not L-jet) THe smaller hose goes to the fuel tank vent. Not sure if this is any help at all, but i can't find anything similar for '79..will keep looking  
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1990 C2 Cabriolet Guards Red  '81 928 Zinnmetallic Project Car (sold)  )'87 944na Maraschino Red Metallic (sold) )
Last edited by surfdog4; 09-08-2008 at 08:19 AM.. |
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09-08-2008, 08:08 AM
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Old 928 Guy
Join Date: Oct 2005
Location: Maryland
Posts: 408
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..forgot the key
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1990 C2 Cabriolet Guards Red '81 928 Zinnmetallic Project Car (sold) )'87 944na Maraschino Red Metallic (sold) )
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09-08-2008, 08:35 AM
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Registered
Join Date: Mar 2008
Posts: 20
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Thanks guys...
It's the small vacuum line that actuates the purge valve, I'm trying to find. From what I understand, it opens when operating temperature is reached. Thus it's plumbed into a temp switch such as the one used for the EGR. I wasn't sure if it spliced into the same circuit or not. ...And my charcoal cannister is a 3 port, BTW. Last edited by koldcustoms; 09-08-2008 at 09:59 AM.. |
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09-08-2008, 09:56 AM
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Network Native
Join Date: Jan 2007
Location: SoCal
Posts: 10,349
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Does 21 the thermal switch open or close when the motor warms up?
I think it opens, which means you get vacuum after the motor is warm, if the purge valve opens with vacuum, then I would say go for it. Getting all the vacuum lines connected correctly without leaks makes the motor run so much better. |
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09-08-2008, 10:08 AM
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Old 928 Guy
Join Date: Oct 2005
Location: Maryland
Posts: 408
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based on my '81 tech bulletin, the temp switch was added in the '81 model year..before that, it says the purge valve vacuum was connected to the throttle, sharing the port with the vacuum advance on the distributor..so it looks like the difference is the newer system blocks venting the canister until the engine is warmed up. I suppose that makes some sense because they go to some trouble on the L-jet to provide a "rich" mixture on warm up..another air source would hinder that somewhat.
For sure you must have the older scheme if you have a 3-port canister (where does the 3rd port go i wonder?) Sounds like if you wanted to hook up the purge valve to another, temp dependant vacuum source it wouldn't be a problem.
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1990 C2 Cabriolet Guards Red '81 928 Zinnmetallic Project Car (sold) )'87 944na Maraschino Red Metallic (sold) )
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09-08-2008, 11:05 AM
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