LS6 Manifold Issue?

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Apr 22, 2006 | 07:34 PM

RocketVette

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6th Gear

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LS6 Manifold Issue?

My father and I just got finished installing a LS6 intake manifold on his 1999 Convertible. When we fired up the engine we heard a hissing sound which we think is coming from around the manifold. No warnings or errors came up on the dash and everything else seems to be running fine. We then fired up my 2004 Coupe which is basically stock. I definitely hear some hissing from my engine but it does not sound the same as his engine nor is it as loud. Is this just the way the engine is going to sound now or did we not hook up something? He also has a Blackwing air filter and a BBK (80mm) throttle body. Thanks for any help you can provide.

Apr 22, 2006 | 09:38 PM

FixedRoof

Melting Slicks

Joined: Mar 2003

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From: FL

Cruise-In VI Veteran

There is a small vacuum line on the rear of the intake.. it pops off VERY EASILY and is easily overlooked. It controls the opening and closing of the a/c ducts and stuff..

Apr 23, 2006 | 04:32 AM

LS9

Safety Car

Joined: Apr 2005

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Quote:

Originally Posted by FixedRoof

There is a small vacuum line on the rear of the intake.. it pops off VERY EASILY and is easily overlooked. It controls the opening and closing of the a/c ducts and stuff..

Apr 23, 2006 | 10:12 AM

RocketVette

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Thank you for the replies. At the back of the manifold I remember connecting two things. One was the electrical connector to the MAP sensor and the other was a vacuum hose that I believe runs over to the power brake booster (but I would not call this hose small). I do remember there being a smaller hose connection at the back of the manifold but the only thing that was connected to it was a small right angle piece of rubber tubing. Is something suppose to be attached to this right angle piece of rubber tubing? Thanks again.

Apr 23, 2006 | 11:44 AM

MrLeadFoot

Melting Slicks

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From: Folsom Lake CA

Quote:

Originally Posted by RocketVette

Yes, an airline that controls the a/c ducts, just as the poster said above.

Apr 23, 2006 | 01:06 PM

RocketVette

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Thank you. I will make sure that hose gets connected. Also, while I have been searching for the answer to this problem I found some threads which mentioned the need to modify the bottom of the LS6 manifold so it fits around some tubes which sit on top of the LS1 block. We never made any modifications to our LS6 manifold before we installed it to the 1999 LS1 engine. When we installed the manifold it seemed to fit flush with the block and there were no issues with screwing the manifold down. This leads me to believe we did not crush any tubes between the manifold and the block. Are these modifications to the manifold really needed? Thanks.

Apr 23, 2006 | 01:40 PM

Bill Curlee

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From: Anthony TX

CI 6,7,8,9,11 Vet

St. Jude Donor '08

Here is just the picture that you need!!!!!

The small fitting below the electrical connector is the one everyone forgets to connect or lets it fall off;

The plastic tube and rubber elbow is NOT very long and difficult to get connected properly:

If your HVAC system will NOT shift the air flow from upper to lower ducts and all of the air flow dumps out of the defrost all the time, thats a dead give away that you left that line disconnected!

Bill C