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

CruiserTrash

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I'm trying to figure out, in all his wisdom, what Mr. T was thinking. I've been studying the Hot Air Intake and Hot Idle Compensation systems after I noticed my HAI diaphragm was always up - always feeding the engine hot air - no matter if the engine was hot or cold.

Before I go on: I'm in Denver and have to keep all my smog gear. My 60 runs great but I'm a meticulous guy and want to get to the bottom of this. I've also tested my HIC per the FSM and it absolutely works.

At cold conditions the middle nipple on the HIC is supposed to route vacuum from the PCV hose to the HAI and pull the diaphragm up. Great, some hot air off the manifold to help warm things up faster, a little feedback loop of heat. At hot conditions, however, the HIC is supposed to open up and allow the PCV vacuum to draw fresh air from the air cleaner in through the PCV hose to the base of the carb (bypassing the carb) to lean the mixture out a bit. Great, I guess, for emissions at idle when the heat of the motor is just sitting there. Photos of Emissions FSM below.

Here's where I'm stuck though. At all three levels of "hot" shown in the FSM, the diagram shows air coming OUT of the middle nipple TOWARDS the HAI diaphragm. This ought to keep it closed and let fresh/cold air into the air cleaner. This doesn't make sense to me though. Once the HIC is open, the PCV hose is providing the strongest vacuum (from where it originates at the base of the carb/manifold) - at the top of the HIC is a weak vacuum/atmosphere, and at the middle nipple you have a dead end at the diaphragm of the HAI. Of course the diaphragm is going to be sucked closed. See my hand-drawn diagrams.

So am I reading these two circuits wrong? Did Mr. T draw the diagrams in the FSM incorrectly or - gasp - design the circuit the wrong way? Is the engine supposed to just be drawing hot air all the time? i's love to hear some thoughts.
 

CruiserTrash

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CruiserTrash

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And here's the abbreviated version of my question. This is how Mr. T shows it in The Book.
 

Spike Strip

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The problem is the HIC valve is bad. It never opens to atmosphere to break the vacuum and let the HAI flap, drop.

HIC valve is long NLA from Toyota and I've got a jar of five of them and they are all bad. In fact, I've never seen one that works. I've tried to find a substitute from other Toyota vehicles and all are NLA...

Stick a 'BB' in the line so the HAI flap at least stays down and you're getting cool air intake. That's what I did.

Maybe you can fid a substitute or work-around for the faulty HIC, but I gave up, mostly 'cuz I'm not too worried about cold-start warmups in Los Angeles.
 

CruiserTrash

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@Spike Strip
It tested good per the FSM, although the test was pretty basic.

If you look at the diagram in the FSM, though, it looks like it's two valves - and both appear to open up with heat. It seems like with cold the valve between PCV (vac source) and HAI should be open and PCV to atmosphere should be closed. With hot temps PCV-HAI should close and PCV-Atmosphere should open. The diagram shows that when hot all three ports - PCV, HAI, and atmosphere are open to each other at the same time.

This is where I'm thinking "I know I shouldn't say it, but did Mr. T draw the FSM diagrams wrong?". I mean who am I to question the engineers??
 

Spike Strip

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It's possible the diagram is wrong. It looks right to me, but honestly, I never studied it too much. I just boiled the valves I could get my hands on and some did move and I got varying degrees of change through the ports, but none of them would work while in the air cleaner. The idea, I gather, is to only allow filtered air into the engine when the valve is in the open (atmosphere bleed) state.

Maybe you'll be more tenacious than I and have better luck.

Let us know what you discover.
 
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I had the same problem man, HIC tested ok outside the air cleaner but not while mounted in the air cleaner housing. I just installed a plug to the hose going to the HAC. I once called Specter and they had a few but never tested I just gave up all that matter is what comes out of the tailpipe.
 

OSS

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As Spike mentioned, the HIC valve may be malfunctioning.
I noticed when playing with and testing mine that the HIC valve has a very long slow delay actuating the HAI flapper on the air cleaner neck.

The HAI flapper very slowly moves a little bit one way or another when the engine is running and different temperatures are applied to the HIC valve.
Maybe my HIC was defective too, but it did seem to do something.
I know when driving on cold mornings that it did shut off the fresh air intake because I could feel it when checking the air cleaner neck opening with my hand.
 

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@OSS That's exactly how it's supposed to work. If you look at the Emissions FSM there are three "hot" conditions : 85*-122*, 122*-185*, and 185*+. At each "hot" condition the flap height will vary. That info is at the table at the bottom of the HIC page (3-38), NOT on the HAI page. What this thing is doing, however, is just varying the vacuum pull it's introducing to both systems which will have a varying effect on both.

Both of mine seemed to test good, but they seemed like they were closed and then full open within a very small temp range and that may be the issue. perhaps the valve itself has been wallowed out with use & time so those middle temperatures are no longer opening in the partial way they should. The vacuum applied to the HAI that I'm seeing is STRONG. Haven't put a gauge on it, but it sure lofts that damn flap right up in a hurry.

@vipergrhd I get kind of OCD about this stuff in an engineering sense, I'm fascinated by how it all works and like a challenge. No, it's probably not a super critical system - not for how the engine runs or the tailpipe emissions. In theory it should have a some effect though. That valve is controlling fresh air that bypasses the carb and goes straight into the intake manifold, so it's definitely changing the mixture. I might kill the whole system by plugging the vacuum source (the tee on the PCV hose) and see what my air/fuel gauge tells me.
 

Spike Strip

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FWIW, I flirted with the idea of just sticking a VSV (on/off) into the line going to the HAI diaphragm and splicing off to direct manifold vacuum, then wiring a switch into the cab so when it was cold day and I wanted a faster warmup, I'd flip the switch to close the HAI flap up, then close the flap after warmup.

Never did install it, cuz as I said, it's just not really an issue in S. Cal. For you, warmups may be a different story.

You can get cheap Japanese-made VSV on rockauto or even cheaper Dorman (Taiwan) on ebay.
 

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@Spike Strip I was thinking about that sort of thing this morning, but in a mechanical-only sense. Get some kind of VSV with a bimetal controlled valve that's set to a fixed temp. It'll raise the flap on cold start ups (to draw hot air) and then lower it when the temp is, let's say 80* (and begin sucking cold air). The engine bay on very cold days would probably take 3-5 minutes to get to an ambient temp of 80* and the flap would help during that time.

The HIC (fresh air that bypasses the carb) is a whole other thing. The whole thing seems like an afterthought .... "Oh this PCV over here has vacuum on it and is nearby to where this hot air intake VSV is already - what if we plumbed them together and could get a mixture-altering affect." it's possible that it was slapped on there out of convenience just because it was close by and they already had an existing tee part they could use for the vacuum plumbing.
 

Spike Strip

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Yes, the whole setup is ridiculously complex. A simple Bi-metal spring on the flap, like 99% of other vehicles of this vintage, as well as other Toyotas, would have been more than enough... But Toyo engineers were probably dealing with stringent smog standards of the day on an engine that's dirtier than a DC Politician.

A BVSV would work fine, like the two in the lower thermostat housing, but unless you're desmog'd and can re-purpose those valves, there's no place else to mount them (since they need coolant contact), that's simpler than an Open/Closed VSV. I suppose one could splice into a coolant/heater line with an in-line adapter, but for me an electrical switch would be an hour install... I dunno, but there may be ambient temperature valves available; I've never looked.
 

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@Spike Strip I actually thought about a BVSV too. The topmost one in my 60 (purple, less than a year old) is disconnected (for reasons I'm still sorting out). I really could use that one right away as an experiment. I could also use tees when I get that circuit working again and piggyback the hot air intake flap off that.

Back to the HIC functionality, I could use the BVSV as a control signal to trigger a VSV (one of the black and white ones - there's two of that type already in the engine bay and I have spares). The VSV could act as the "fresh air injection" into the manifold. It would be on/off unlike Toyota's original HIC design that was supposed to allow fresh air into the manifold along a continuum, but at least it would WORK.

I need to run some tests with the HIC disabled, with the HAI run off the purple BVSV, and with my spare VSV as the HIC controller and air intake. Like I said I have an air/fuel gauge I can watch along with my butt dyno statistical analysis. A lot of work for systems that don't make a huge difference but oh well.
 

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Yes, I have an A/F meter, too. I have the whole HAI system hooked up with exception of the HAI Diaphragm, which is disabled. However, when the engine and ambient air is very hot, and under-hood temps climb because of idling, I get some weird readings first going rich, then lean... I've been trying to figure that out for 10 years ...

Now, re-reading the posts of the FSM pix, I'm thinking it might be this stinking valve! Never put 2 'n 2 together! (middle of picture)

I'm gonna have to block off the port to the PCV 'T' and see what happens.

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CruiserTrash

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How fast is the A/F gauge fluctuating between rich and lean? And what's the range you're in?

As far as the HIC circuit goes, both of the valves I have seem to go full open (fresh air coming into PCV intake on manifold) at like 90*. Doesn't take much for temps in the engine bay to get to 90. Again, my testing wasn't scientific - I held the metal portion of the valve in the water and covered the HAI nipple while my son pushed on a vacuum pump that was plumbed to the PCV nipple. There didn't seem to be much middle ground or a soft opening. Just open or closed. So all that air is coming in leaning out the mixture.

Really good info to have for tuning the carb. Since I'm smogged I need to be accounting for that extra fresh air. The frustrating part is that it probably doesn't affect the amount of gas used or mpgs, since the carb is doing it's thing as if this extra fresh air didn't exist.
 
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The diagram is saying that once the top portion of the valve is open (the atmospheric portion), the entire body of the valve will be at atmospheric pressure. The assumption is that the atmospheric portion of the valve will flow more than enough air to keep the flap valve open regardless of what the HIC portion is doing.

Don't forget, the HAI sensing element is up in the air-stream. It's sensing the air temperature inside the air cleaner - not the air cleaner temperature. You'd need a thermocouple in the same area as the valve to determine whether or not it was actually working correctly.
 

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@Lead Head I'm not sure I'm clear on what you're saying. Are you suggesting that because the body of the valve is at atmospheric pressure that it will "push" the HAI flap closed and allow cold air to enter the air cleaner?
 
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The HAI valve is spring return. It naturally wants to block off the hot air riser tube. When the HIC is closed to atmosphere, the HAI port is exposed to manifold vacuum. When the HIC valve first opens, it exposes the the HAI port to atmospheric pressure. Once the vacuum in the middle port goes away, the HAI flapper will return closed under spring pressure.
 

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The HAI valve is spring return. It naturally wants to block off the hot air riser tube. When the HIC is closed to atmosphere, the HAI port is exposed to manifold vacuum. When the HIC valve first opens, it exposes the the HAI port to atmospheric pressure. Once the vacuum in the middle port goes away, the HAI flapper will return closed under spring pressure.
Well, that would make a lot of sense and both systems would operate in a logical way if that was the case, but that is where the FSM isn't super clear. The diagram appears to show that under a hot condition that all three ports on the valve (atmosphere in the air cleaner, HAI nipple, PCV vacuum nipple) are connected - sharing the same air if you will. In the presence of a vacuum, anything at atmospheric pressure will try to reach equalibrium by getting "sucked" towards the vacuum.

Instead of all three sharing the same air when the HIC is open, you would think the Atmosphere<->HAI nipple, atmosphere<->PCV nipple, & HAI nipple<->PCV nipple would be three independent passageways. When cold only the HAI nipple<->PCV nipple passage is open and the other two closed. When hot the HAI nipple<->PCV nipple passage closes and the atmosphere<->PCV nipple & atmosphere<->HAI nipple both open. I think the error that is happening is that when hot the HAI<->PCV nipple is open under hot conditions - so all three interfaces are open to each other and the HAI nipple is getting vacuum at both hot and cold - hence the flap is up all the time. But that seems to be exactly what the FSM diagram is showing. So is the HIC broken (HAI nipple<->PCV nipple not closing when hot) or did Toyota good and design the HIC that eay (hence why the diagram is drawn how it is)?

See diagrams from the Emissions FSM below. Yes, I am ignoring the "partial" opening of the valve at temps between 81* and 185* for simplicity's sake. The same thoughts apply to the partial opening conditions too.
 

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