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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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 Posted: Fri Aug 18, 2017 8:57 am Post subject: Vacuum leak issue |
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Since I swap the S2 intake to the GTS intake along with the FMIC, my vacuum gauge reads between 12-14 inch and run rough at idle.
I just ran a smoke test and only the charcoal canister line showed leaks, so I bypassed them and it didn't changed anything.
I ran different test to try to isolate the problem source to find out that the if I pinch the line mark in red bellow, the vacuum goes back to regular reading (about 18 inch).
Why is a vacuum line (post throttle body) is connected directly to a pre-throttle body.
This thing is driving me crazy
Thanks
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Sat Aug 19, 2017 6:53 am Post subject: |
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Anybody have any idea of the purpose of this line (in red above)?
Any foresee/possible problem if I delete it?
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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morghen
Joined: 21 Jan 2005
Posts: 9095
Location: Romania
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| Posted: Sat Aug 19, 2017 7:52 am Post subject: |
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Dont delete it, thats not the root cause of your problem.
I'm no expert in engine vacuum systems but i think that line network feeds vacuum to the break booster and the line you marked limits the vacuum to the booster by limiting the post TB vacuum.
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Supercharger and EFI kits
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Sat Aug 19, 2017 8:32 am Post subject: |
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| morghen wrote: | Dont delete it, thats not the root cause of your problem.
I'm no expert in engine vacuum systems but i think that line network feeds vacuum to the break booster and the line you marked limits the vacuum to the booster by limiting the post TB vacuum. |
morghen, thank you for the info.
Before the intake swap, I was pulling 17-18 inch. I check my vacuum routing 3 or 4 time to make sure everything is plugged at the right place.
The one thing I changed is I'm not using the black air tube that connect to the AAV, decel valve, brake booster and intake manifold. I just used "T" brass fitting and robber hose following the same same routing.
I marked in the diagram below where was and still is connect my vacuum/boost gauge. Wrong or right location?
Thoughts?
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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924-76
Joined: 05 Jun 2006
Posts: 1489
Location: Ontario, Canada
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| Posted: Sun Aug 20, 2017 5:01 am Post subject: |
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Got it! 
Problems:
1- The Auxiliary Air Valve (AAV) was stock 1/3 open; once fixed it was not that largely open at ambient temperature.
2- One of the wire in the AAV connector had backed out and was not making connection.
I just came back from a 45 min drive back country road and highway and everything worked as expected.
Thanks
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP |
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