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Discussion Starter · #1 ·
I am doing the finishing touches on my 5.3L LS swap and getting ready to take my '56 LS out for the first time. The thing starts great and idles smooth. One thing that concerns me is the vacuum pressure. It seems like my vacuum pressure is WAY too high. I tried to remove the oil filler cap and it was almsot stuck on there. I had to pull very hard to remove it. Even the dipstick is the same way. I need to buy or borrow an ODB2 scanner to see if I am putting up any codes, but does anyone have any ideas why an LS might have that much vacuum pressure? Or could this be normal? What is the best method to test vacuum pressure and what is "normal" pressure? (MAP sensor reading?) :confused0024:
FYI- Engine is an LM7 truck motor with an LS1 intake, headers, 2 1/2 dual X pipes and 4L60E trans.
Thanks for your ideas!!
 

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Discussion Starter · #3 · (Edited)
I believe the PCV is routed correctly Bo. I actually saw a diagram you posted on another thread (below.) I did not route the passenger side through a catch can, just directly into the intake manifold behind the throttle body. The driver's side is routed to this general area as well.
 

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Ok, reread you have an LS car intake.

The pass side goes to the goes to the TB itself. Should be a fitting on the TB for it. The drivers side goes the the fitting on the intake or valley cover port if LS6 intake. Verify routing or post a picture.

Normal MAP at idle. 35-40 kPa or 10-11 inHg

The crank case is sealed to provide PCV of oil fumes. So it will have some vacuum on it at idle. As to how much never really thought about it, should be same as MAP though.
 

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Discussion Starter · #5 ·
I am using the stock TB from the truck motor (2005 Tahoe) which does not have a port on the TB. I see that the Camaro (where the LS1 Intake came from) has a port on the TB for that purpose. I connected the drivers side to the port just towards the inside of the TB on the intake neck. The car is at a friend's house so I'll have to get over there to take pics.
 

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I am using the stock TB from the truck motor (2005 Tahoe) which does not have a port on the TB. I see that the Camaro (where the LS1 Intake came from) has a port on the TB for that purpose. I connected the drivers side to the port just towards the inside of the TB on the intake neck. The car is at a friend's house so I'll have to get over there to take pics.
That's the problem I believe its not getting any fresh air so the vacuum is spiking inside the case.

The pass side can be ported directly into the intake tube as well just needs to be aft of the MAF. And it will be the inlet. Since its aft of the MAF it will idle the same.
 

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Discussion Starter · #7 ·
That could be it. So if I tap into my cold air intake tube, aft of the MAF but before the TB, it should solve the prolem. I guess I didn't understand the flow of the PCV system, but it makes sense. If both ends of the PCV system are connected to the intake then there is no flow and both sides are under vacuum. I'll test that solution out. Thanks!
 
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