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I am starting on trying to clean up my engine bay.  I noticed a vacuum line running from the cabin and just  hanging down unconnected behind the fuel vapor canister.   Looking at the service manual I see two vacuum lines running from the cabin, one to the control valve on one of the heater lines (that works by the way as I have tested it).  The other to the vacuum tank.  I do have a line going from the vacuum tank into the cabin but that one runs thru a opening near the break booster.  On the diagram in the shop manual I see no other vacuum line running from the cabin thru the firewall only those two so I have not idea what this third vacuum line should be doing, if anything.  The line that runs from inside the cabin (from the climate panel) to the vacuum tank) is a larger diameter hose then the one I am questioning. 

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Edited by jscott
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Should have all black vacuum line from cabin to canister.  Should have another line from canister to a vacuum source on manifold.  Other one from cabin should be black with purple stripe to valve module in heater hose.   Does the third line coming out have any kind of color stripe on it?

Kilgon

 

 

"The only dumb question is the one not asked"

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54 minutes ago, jscott said:

all are plain black, there is the line from the canister to the vacuum source on the manifold.

Look hard at the line going to the valve for the purple stripe.  Maybe lines were replaced and the loose line is abandoned.  The 71 with a 429 had a electonic distributor  modulator under the dash but this had 2 lines going  to it.   Not for sure if any of the the 72's had it.. They went through the firewall by the brake booster.  Can you try to see where it goes in the cabin.   Have someone push- pull it while you look under the dash.  Don't know of any others that run through the firewall. Was there a PO.  Perhaps they had  a vacuum gauge or something hooked up inside that needed it  .

Edited by Kilgon

Kilgon

 

 

"The only dumb question is the one not asked"

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Vacuum gauge is a good guess. Another not so good guess is back when these cars were new water and alcohol injection systems were popular, as people tried to do things to overcome the effects of the low octane non-leaded fuel. I've even seen people run a rubber hose from inside to the intake manifold and connect the nozzle from starter fluid to it, for cold weather starts, probably not needed in Georgia, though 🙂

Edited by Don C
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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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thanks for the quick responses.  Just looked again, the one hoe from the cabin to the valve on the water heater hose has a red (aged) stripe.  The loose one that I am questioning does not, I want to think it had one but cannot define any color.  It is a small diameter hose that would fit perfectly on the canister.  The hose on the canister now that runs thru the firewall near the brake booster is a larger diameter hose, no colors.  I did track that one down to the climate control panel back, about 8" before it gets there is is jointed to a connector to a slightly smaller hose that goes into the back of the panel.  I wonder if, at one time they lost the connection with the hose that is loose and ran a new one near the brake booster in it's place.  Wonder if I make a T connection to give the non connecting one some vacuum or could that cause a problem somewhere?

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The faded red is really purple.   Your original black one off the cannister should have been connected to a brown one that goes to the climate control.   Based on the info I'm going to say they replaced the original with the one running through by the brake booster.  More than likely the original had a leak.  You could try and swap them at the connector but if it is all working okay I would leave it alone.

Kilgon

 

 

"The only dumb question is the one not asked"

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