HAI, HIC, and drawing hot air all the time ... just the way it is?

CruiserTrash

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I don't know why but the diagrams got stuck in the part that quotes your post. Hit "expand" to see them.
 

CruiserTrash

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95BBCD4C-4E68-41A1-8317-496DBCF72E93.jpeg
Just stopped at OReilly for testing supplies.
 
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There is no ambiguity with their diagrams.

The manifold vacuum port is always allowed some flow. When the main atmospheric vacuum port (the one on top) is closed, this causes vacuum to be applied to the HAI motor. When the temperature actuator starts to open the valve, the main atmospheric port opens first. This causes the entire body of the valve to be opened to atmosphere. The manifold vacuum port is still being severely restricted at this point, so very little to no vacuum should be going to the HAI motor since it will largely be at atmospheric pressure.

As air intake temperatures continue to climb, the valve will open more, allowing more atmospheric air to flow into the valve. Simultaneously the manifold vacuum orifice opens more, allowing more air into the manifold. The idea of this is, is it will lean out the idle and part-throttle cruising mixture. This is because hot air is less dense, and needs less fuel to burn. At mid-high throttle, the air intake temperatures will naturally drop because of the increased air flow. High intake temperatures are really only an issue at idle and low throttle when their airflow is slow enough that it has time to pick up a significant amount of heat from the engine bay. But the whole body of the valve will be at atmospheric pressure unless the inlet port is restricted.

It's simple enough to check the operation of the mechanical part of the valve: Unscrew the temperature actuator and poke something into the valve and observe what happens. It's probably just a little stuck and needs to be lubricated.
 
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CruiserTrash

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The manifold vacuum port is always allowed some flow. When the main atmospheric vacuum port (the one on top) is closed, this causes vacuum to be applied to the HAI motor.
100% agree

When the temperature actuator starts to open the valve, the main atmospheric port opens first. This causes the entire body of the valve to be opened to atmosphere.
I'll circle back to this...

As air intake temperatures continue to climb, the valve will open more, allowing more atmospheric air to flow into the valve. Simultaneously the manifold vacuum orifice opens more, allowing more air into the manifold. The idea of this is, is it will lean out the idle and part-throttle cruising mixture.
Also 100% agree

This is because hot air is less dense, and needs less fuel to burn. At mid-high throttle, the air intake temperatures will naturally drop because of the increased air flow. High intake temperatures are really only an issue at idle and low throttle when their airflow is slow enough that it has time to pick up a significant amount of heat from the engine bay. But the whole body of the valve will be at atmospheric pressure unless the inlet port is restricted.
This is the HIC circuit in a nutshell. Well thought out, well designed. I'm not an engine expert so I don't know how big of a difference it makes to idle and part-throttle driving. A little? A lot?

It's simple enough to check the operation of the mechanical part of the valve: Unscrew the temperature actuator and poke something into the valve and observe what happens. It's probably just a little stuck and needs to be lubricated.
I am going to open up my
spare valve today.


So, let's come back to your statement: the entire HIC body is open to atmosphere at hot conditions. That would include both the HAI nipple, the PCV nipple, and the atmosphere port on top in the air cleaner. The PCV port is experiencing a vacuum from the intake manifold. You have atmospheric pressure (low) adjacent to a vacuum (ever lower) inside of the HAC. These two will attempt to reach an equilibrium, but since the engine continuously creates a vacuum you wind up with "suction", a constant flow of air towards the PCV vacuum source. The air at atmospheric pressure can dump into the very low pressure PCV line and never reach equilibrium.

Now let's zoom in on the HAI nipple (and the dead-end hose running to the HAI diaphragm), which we've ignored so far. If the whole HIC valve is wide open at hot like you say, that HAI run is going through this same equilibrium process too. The HAI run is at atmospheric pressure and will end up with the same "suction" towards the PCV nipple as the outside air port does. Hence why it seems to me like the HAI flap would be up and allowing the engine to draw hot air all the time per the design of the HIC.

That is unless the diagram in the FSM is drawn incorrectly and when the HIC "opens" the air-clear-to-PVC-nipple passage is open, but internally the HAI-to-PCV passage is being closed. As it stands it shows both passages open at hot. See the little arrows.
 
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So, let's come back to your statement: the entire HIC body is open to atmosphere at hot conditions. That would include both the HAI nipple, the PCV nipple
The PCV nipple is never directly open to atmosphere. The bottom half of that valve is a variable orifice (restriction). That's why the diagram has that area shaded in black in all 4 operating modes - because it will always be in a deep vacuum.

Take a vacuum cleaner, and tape up the suction hose. Poke a tiny pin-sized hole through the tape. This will represent the engine vacuum (PCV) being metered through a restricted orifice (the bottom part of the valve). Now get a coffee can (this will represent the HIC body), cut a hole in the bottom of the fan to fit the vacuum hose and attached the two. Poke a pen-sized hole on the side of the coffee can (this will represent the HAI port). Now turn the vacuum on.

You will of course feel vacuum pulling through the HAI port. Now, take the lid off. You will now zero vacuum on the HAI port. This represents the atmospheric valve opening. Even if you poke the a bigger orifice through the tape on the vacuum hose (representing the valve opening more), you still will not feel any suction on the "HAI Port". This is because the atmospheric port (represented by the can lid) is much larger than the vacuum port

Basically the atmospheric port opening has a significantly large cross-sectional area than the vacuum port opening. If everything is operating correctly, the atmospheric port will simply flow far more air than the vacuum port can pull, meaning the entire HIC body will be at atmospheric pressure.

Another comparison is this: How come when you open the throttle, you don't have full manifold vacuum on your air filter box? The answer is because the air supply opening is capable of flowing far more air than the engine can pull through the throttle blade.
 

CruiserTrash

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Sorry y'all this has been on hold for the week. My patience for vacuum issues gets the better of me sometimes and I have to run off and do other things for a bit. I'm going to mess with it again this weekend.
 

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