bad HIC valve

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dlb
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My tercel:: '87 sr5, '83 dlx parts car
Location: bc, canada

bad HIC valve

Post by dlb »

My HIC valve is bad. I've never paid much attention to these before but I noticed the HAI flap on this car is always open to the hot air intake, so I looked into it and realized the HIC valve (which controls the HAI) never gets out of its 'cold' setting. I took it apart and it's a similar design to the TVSV in that there is a pin in a chamber that is supposed to rise and fall depending on the temperature, and like most TVSV's I guess it wears out with use.

The effects of this are:

- the HAI flap always takes in hot air, which isn't a big deal in cold weather but wouldn't be great in hot weather,
- the HIC doesn't add the correct amount of filtered air to the intake manifold during idle and highway cruising. I don't know how big a deal this is but I'd like to do something about it if I can.

I don't really care about the HAI so I have just plugged the hose that goes to it from the HIC for now. But I think I might try adding a kind of spacer to the pin in the HIC so it's at least partially open all the time. If I did more long distance drives (my commute to work is 10 minutes) I would probably aim to have the HIC fully open all the time but I think partial will best suit the majority of my driving.

Anyone else have any experiences with this, any suggestions?
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NWMO
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Re: bad HIC valve

Post by NWMO »

David,

I think a few of us have completely disabled the HAI flapper without issue. I don’t notice much/any difference and had no problems to -10 F with starting or driving.

Chris
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dlb
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My tercel:: '87 sr5, '83 dlx parts car
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Re: bad HIC valve

Post by dlb »

Yeah, I'm fine with leaving the HAI disabled. It's modifying the HIC valve so it leans out the mixture like it's supposed to, that I'm interested in.
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Mark
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My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re: bad HIC valve

Post by Mark »

I don't think that system has any effect on the fuel-air mix or does anything to lean out the mix. According to the FSM diagram, it just acts as a switching valve to direct vacuum (or shut it off) to the flap diaphragm. When the HIC valve is open, the vacuum to the flap valve diaphragm should be dead headed and there shouldn't be a flow of air acting like a vacuum leak if that makes any sense.
HIC.jpg
"EDIT" Oops, I for got to read about the other function on the HIC:
HIC2.jpg
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Mark
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My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re: bad HIC valve

Post by Mark »

Looking at those temperatures, I wonder how often the air temperature in the air filter housing would ever get that high in our climate. 29 degrees C, I can see, but over 50 degrees? That's almost too hot to touch. I'd be curious to put a thermometer in the filter housing and see how hot it gets.
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Mark
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My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re: bad HIC valve

Post by Mark »

At that highest temperature (above 89), when you factor in the pressure drop across the filter, that's probably hot enough to boil off water. Maybe this condition would apply if you were sitting at idle for an hour with a clogged air filter (so reduced air flow), in the sun, in Death Valley. Or maybe I'm wrong and these temperatures are common in the air intake system, but I can't see it.
By the way, I don't suppose your Tercel has the feedback carb with the oxygen sensor? Or maybe that was just in automatics like mine?
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dlb
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My tercel:: '87 sr5, '83 dlx parts car
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Re: bad HIC valve

Post by dlb »

I wondered the same thing about the temps -- how could it get that hot in there with air constantly rushing past? I dunno. I put my HIC in near boiling water though and the vacuum port was still fully closed so I figure I'll basically just prop it open a bit with a spacer and try that.

Nope, my car doesn't have the feedback system. It's one of the reasons I like the Canadian manual trans cars, they have less complex emissions systems than most of the others.
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Nordical25
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Re: bad HIC valve

Post by Nordical25 »

I like also less complex emissions systems especially when car gets old. Less parts mean less worries when it comes to 40 years old emissions systems.

Could it be possible to put some kind of lever to switch manually from hot air intake to cold air intake? My third hobby car, an Opel Kadett C from 70's has that kind of system. You can swap between hot air and cold air manually based on temperature. Opel calls positions as "summer mode" and "winter mode". Basically you choose cold intake air during summertime and rest of year hot intake air.

I attached pictures of both air filter housing positions, which I found online. I drive mine during summertime and that's why I use only summer position.
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