HAI, HIC, and drawing hot air all the time ... just the way it is? (2 Viewers)

[CruiserTrash]

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

 

[CruiserTrash]

Just stopped at OReilly for testing supplies.

 

[Lead Head]

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.

 

[CruiserTrash]

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.

 

[Lead Head]

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]

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.

 

[g-man]

I'm curious about this. I just made a heat riser tube to go between the air cleaner and the exhaust manifold shield just below the HAI door. My valve is working like things are cold. I mean the vacuum from PCV hose is pulling vacuum on the HAI port and pulling the door up to the "give me hot air" position.

I drive around and get things warm but still door is pulled up by vacuum. I unscrewed the top of the HIC valve and the metal pin slides easily inside its housing in the top half of the valve. Next time I check this I will remove the top 1/2 and the metal pin and use a small pick to see if I can easily move the bottom half, the actual valving that closes vacuum. I suppose it is plastic with a spring so I could see it getting old/brittle and not wanting to move.

I also have not taken long drive since my repair. My HIC wasn't really that warm and ambient engine temps are going to get it hot. So, maybe a long drive and check again.

 

[Spike Strip]

That valve that Toyota calls an HIC is called by the rest of the world an 'Air Charge Temp Sensor'. I've been noodling about this lately because when the truck is warm and idling I can see on my Air/Fuel meter the mix goes rich, which the Emissions FSM says is usually from fuel 'Percolation' which can lead to vapor lock, which I've never experienced.

Anyway, the LC HIC valve is long NLA, but I've ordered what I hope are very similar valves from similar vintage Toyotas, from Japan- We'll see what shows and if they will work.

As I stated earlier (a year ago) in this thread, I too found my HAI air cleaner flap always up, so I blocked it off with a BB. Not really much of a concern here in Los Angeles, but it would be nice to have everything working as a Toyota Engineer intended.

There are non-Toyota 'Air Charge Temp Sensors' from 70's and 80s vintage that serve the same function of bleeding filtered air into the intake PCV system to compensate for idle enrichment, but do not function as a valve for the Air Cleaner Thermoflap. I might try one of those if the Toyota valves do not work out.

Will post results.

 

[2mbb]

That HIC valve does two things: it controls the vacuum to the HAC flapper valve and it bleeds air into the intake manifold to lean out the A/F mixture once the engine is hot. When the engine is hot the HIC air bleed should be fully open and there should be no vacuum at the HAC. Next time you work on it, take the HIC off the air cleaner and make sure the air bleed hold is not blocked or clogged. The emissions manual has other tests you can perform. Be sure to read both sections, HIC and HAC, to get the most benefit.

At the mid-point temperature, when the HIC air bleed is only partially open, I supposed some vacuum may be going to the HAC. You should also consider that you are doing your inspection at idle, when the manifold vacuum is at its highest. When you are racing around the neighborhood (haha) manifold vacuum may be lower and the HAC may actually be closed.

 

[CruiserTrash]

I realize I never ended up coming back to this! Looking forward to what y'all dig up.

 

[micruz60]

It is clear. . . as Mud!

 

[g-man]

I checked my HAI door today and it closed so cold air coming in the air cleaner. It just took some driving around to get the HIC hot. I drove about 20 minutes each way to the local Lowes and back. Mostly at 55mph. Think about how hot your motor is after you drive a long time. Ambient temps inside the air cleaner are going to be much higher than a cold start in the drive way ...even if you idle for 10 or 15 minutes and the temp gauge shows normal op temps.

 

[CruiserTrash]

I checked my HAI door today and it closed so cold air coming in the air cleaner. It just took some driving around to get the HIC hot. I drove about 20 minutes each way to the local Lowes and back. Mostly at 55mph. Think about how hot your motor is after you drive a long time. Ambient temps inside the air cleaner are going to be much higher than a cold start in the drive way ...even if you idle for 10 or 15 minutes and the temp gauge shows normal op temps.

So you’re saying the HIC doesn’t drop the hot air flap until it gets REALLY hot. Not just “up to full temperature” from idling in the driveway for 15 minutes … but blazing hot, high rpm cruising?

In other words, for some reason Toyota thought sucking in hot air would be a good idea for the motor to breath hot air in under idle and “around-town” conditions, but allow fresh cool air only when the motor is running super hot, say on the highway?

 

[Spike Strip]

So you’re saying the HIC doesn’t drop the hot air flap until it gets REALLY hot. Not just “up to full temperature” from idling in the driveway for 15 minutes … but blazing hot, high rpm cruising?

In other words, for some reason Toyota thought sucking in hot air would be a good idea for the motor to breath hot air in under idle and “around-town” conditions, but allow fresh cool air only when the motor is running super hot, say on the highway?

Yeah, according to FSM, above 91* F Flap should be open (down). 91* under the hood happens very quickly, but let us not forget, this is using intake, filtered air. In any case, if the flap is closed when engine warm that's no bueno.

 

[CruiserTrash]

Yeah, according to FSM, above 91* F Flap should be open (down). 91* under the hood happens very quickly, but let us not forget, this is using intake, filtered air. In any case, if the flap is closed when engine warm that's no bueno.

And that loops back around to my first couple of posts. The flap stays up, letting the engine draw hot air even after it is fully idled up to operation temp, AND after city driving. I’ve never pulled off the highway to check.

Going back to those first few posts though, that seems to be the way Toyota draws the HIC operation in the FSM. And that’s why I was scratching my head.

 

[g-man]

Yeah, according to FSM, above 91* F Flap should be open (down). 91* under the hood happens very quickly, but let us not forget, this is using intake, filtered air. In any case, if the flap is closed when engine warm that's no bueno.

No, the filtered intake air is only feeding into the bottom of the HIC to pull vacuum. Although that air also is moving around inside the valve and contributes the temps. The air around the top 1/2 of the HIC in the air cleaner is what is heating the Valve up to actuate it. There is a top knob and the brass metal under it is threaded. This is the part that gets hot and pushes the pin down. I put a rag on the top knob and twisted it loose with pliers. The top comes out and you can see the pin and the metal housing it sits in just under the knob. I oiled mine lightly. It moves in and out easily. The HIC gets hot, expands pushing the pin downward to open the valve at the bottom. While at idle I was able to take the top off my air cleaner and put my hand on the top part. It was barely warm to the touch. I could also put my hand on top of the power steering pump, the alternator etc. NOW, imagine pulling off the interstate and the engine compartment is really hot. You can't put your bare hand on top of any of those things, or at least not for very long. So it's not the engine temp at the temp sender on the head that determines when the valve opens, it's the ambient temp inside the air cleaner at the top of the HIC valve.

 

[Spike Strip]

Just an update:

Replaced the inoperative HAI / HIC valve with this one from a early 90s Isuzu and it works perfectly.

Had to clearance the washer that came with it because I didn't want to modify the Air Cleaner, just in case.

That valve is available under a few different parts # and brands. Don't have at the moment.

 

[CruiserTrash]

@Spike Strip I completely forgot about this! Maybe I’ll have time to dig back in on the OE side of things, and beyond that test the Isuzu unit per the Toyota FSM and see if it operates to similar parameters.

 

[Spike Strip]

There's a bunch of these types of Temperature valves on ebay, usually for GM or Ford, and any of them should work, as they all have essentially the same function.

I noticed a FJ60 air cleaner that BTB products had 'Remanufactured' used one of the GM type. You can see it on their website