Opti vent harness check - Chevy Impala SS Forum
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post #1 of 15 (permalink) Old 04-16-2012, 08:23 PM Thread Starter
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Opti vent harness check

Im curious if there is a good way to check the opti vent harness more than just visually. My main concern being the one with the check valves. Check valve orientation is one way, allowing vaccum into the opti right or wrong?
Was going to replace put appear fine but figure id make sure everything flowing to right way. Gm replacement is pricy, but if i could make my own that would be cool. Just not fully understanding how the harness works.
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post #2 of 15 (permalink) Old 04-17-2012, 05:48 AM
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I know I saw a recent thread on this. Did you try a search on the Forum?

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post #3 of 15 (permalink) Old 04-17-2012, 10:12 AM
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the "blue" part of the valve goes towards the intake

\'96 BBB 383/T-56
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post #4 of 15 (permalink) Old 04-17-2012, 03:31 PM Thread Starter
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ok looks like i had the larger (check valve) backwards.
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post #5 of 15 (permalink) Old 04-17-2012, 05:42 PM
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on mine the blue part is on the opti side

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post #6 of 15 (permalink) Old 04-17-2012, 06:44 PM
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Opti vent harness check

The "blue" side of both valves faces the manifold (away from opti) I cannot overstate the importance of these valves pointing in the right direction. Verify proper ventilation. Either with a vacuum gauge (the best way) proper ventilation is indicated by the gauge slowly raising until manifold vacuum is reached,or with a piece of paper (common,but crude). Many cases of opti failure can be directly linked to ventilation,or lack thereof.
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post #7 of 15 (permalink) Old 04-18-2012, 10:58 AM
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Verify proper ventilation. Either with a vacuum gauge (the best way) proper ventilation is indicated by the gauge slowly raising until manifold vacuum is reached,or with a piece of paper (common,but crude). Many cases of opti failure can be directly linked to ventilation,or lack thereof.
are you saying Opti vacumn should read what the manifold vacumn is (18-19 in HG) at the blue nipple that goes into the rubber intake elbow?

Mine reads 4 at that point. It reads 18-19 on the hose that has the blue valves that plugs into bottom of Opti

\'96 BBB 383/T-56
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post #8 of 15 (permalink) Old 04-18-2012, 12:43 PM
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Opti vent harness check

Yes,or at least close to it. I've heard of cleaning the check valves with alcohol (not on the car) you may have a vacuum leak in the check valve,or more likely where the hose meets nipple. Check hose snugness at the opti itself. New lines aren't that expensive,get "fuel injection" line if possible. It holds up much better. At least cut 1/2" off each end of the existing lines,for more secure connections if you aren't prepared to swap out the lines.
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post #9 of 15 (permalink) Old 04-18-2012, 01:16 PM
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Originally Posted by 1slow96 View Post
Yes,or at least close to it. I've heard of cleaning the check valves with alcohol (not on the car) you may have a vacuum leak in the check valve,or more likely where the hose meets nipple. Check hose snugness at the opti itself. New lines aren't that expensive,get "fuel injection" line if possible. It holds up much better. At least cut 1/2" off each end of the existing lines,for more secure connections if you aren't prepared to swap out the lines.
The blue nipple on vent hose does not have check valves. It runs straight to Opti. That line reads 4 in vac. The line with the check valves reads 18

This is a brand new vent harness, GM

The line that goes to the blue nipple fits the metal nipple on Opti and the line that goes to manifold has 2 check valves and goes to the larger "plastic" nipple on the Opti.

also this is a comment from Rocko about opti vent vacumn

"The disc looking thing in the opti harness is a vacuum limiter. designed to limit the vacuum to around 4inches i believe. It does need to be able to hold a small piece of paper. "

\'96 BBB 383/T-56

Last edited by BALLSS; 04-18-2012 at 01:22 PM.
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post #10 of 15 (permalink) Old 04-18-2012, 02:02 PM
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Opti vent harness check

All this is in the FSM. I want to help,but I'm weary of the endless debating about every little thing that this forum has become. If the vacuum was limited,then how could you have 18in. at the opti ,but the line with nothing on somehow reads 4in. If you've checked that line for a leak,then the only thing that occurs to me is that the opti itself is no longer sealed.
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