TwinTurbo.NET: Nissan 300ZX forum - Throttle body vacuum ports are confusing.
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Subject Throttle body vacuum ports are confusing.
Posted by 300NASeattle on July 04, 2018 at 1:29 PM
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Message Can anyone explain the purpose of the vacuum ports on the underside of the throttle bodies for me. I assumed that they allowed manifold vacuum at all throttle positions where vacuum ports in front of the throttle bodies (along the intake pipes) only provide vacuum when the throttle is open.

I found this to not be the case when I was doing some engine cylinder cleaning with water and some Seafoam and using the throttle body vacuum ports to suck in the liquids. They do only provide vacuum when the throttle is cracked. This is confusing since the EGR solenoid has one connection to the throttle body port and another to the intake pipe.

I did notice that the vacuum port on the passenger throttle body was a much weaker (or non-existent) vacuum at the same RPMs versus the driver's side throttle body vacuum port. There was strong vacuum on the drivers side from 1500 - 2000 revs but I had to go up to 3000 revs to get vacuum on the passenger side. I ended up using the balance tube vacuum port closest to the battery to suck in the water and Seafoam. I could easily blow into the vinyl hose I attached to the passenger side throttle body vacuum port - there were no blockages.

Is there supposed to be a stronger vacuum at the throttle body ports versus the intake pipe ports, due to proximity to the the throttle plate or possibly a venturi affect?

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