Two Quick Questions for you Emissions "Smart Guys" (1 Viewer)

[Rocky_LC]

I have an '85 2F transplanted into my FJ-40. Much of the emissions stuff has been retained IAW guidance from this Forum.

I had two quick questions:

1. What is the purpose of the lower port on the HAC Valve (Not the big one, which I understand should be open to the air...). Should it be connected to anything?

(Note: I am pretty certain my HAC Valve works, because as I get my truck above 6000', I have more power than I do down below. I think it is advancing the timing. I am just curious about this one).


2. What is the difference between an Aisin 90925-05035 (brown body) and an 90925-05046 (pink body) vacuum device (it screws into the thermostat housing). What happens if you interchange the two? The barbs broke off the brown one (-05035) and all I have as a spare is a pink one.

(My guess on this is it operates at a different temperature?)


Thanks -

Rocky

 

[OSS]

The bottom port of the HAC valve is a fresh air source. Any time the engine is running, a small volume of air is getting sucked up through that port. Even at sea level, there's a small vacuum leak built into the HAC system.
There's an air filter at the bottom of the valve that should be cleaned or replaced every decade or so. Bottom of the valve snaps off. Filter easy to get at.

Yes, those two sensors screwed into the thermostat housing are affectionately referred to as BVSVs. They're thermo-switches that open when the coolant reaches a certain temperature. One is used in the EGR system to prevent it from functioning when the engine is cold, the other is for the Choke Opener system to prevent it from working when the engine is warm.

The emissions manual (attached) explains what is what.

 

[Rocky_LC]

Thanks for the manual.

I hadn’t considered the BVSVs might be “opposite polarity”.... normally open vs. normally closed.

I’ll have to do some reading here soon.

Thanks again -

Rocky

 

[OSS]

They both open when the coolant warms up. Different temperatures for each. It's their associated system they're plumbed into that dictates what happens when the air passage opens.

 

[Don Pedro]

The bottom port of the HAC valve is a fresh air source. Any time the engine is running, a small volume of air is getting sucked up through that port. Even at sea level, there's a small vacuum leak built into the HAC system.
There's an air filter at the bottom of the valve that should be cleaned or replaced every decade or so. Bottom of the valve snaps off. Filter easy to get at.

Yes, those two sensors screwed into the thermostat housing are affectionately referred to as BVSVs. They're thermo-switches that open when the coolant reaches a certain temperature. One is used in the EGR system to prevent it from functioning when the engine is cold, the other is for the Choke Opener system to prevent it from working when the engine is warm.

The emissions manual (attached) explains what is what.

Manual is mostly Greek to me but will print it out so it's handy for mechanic. Good stuff.

 

[Gretsch]

1. What is the purpose of the lower port on the HAC Valve (Not the big one, which I understand should be open to the air...). Should it be connected to anything?

(Note: I am pretty certain my HAC Valve works, because as I get my truck above 6000', I have more power than I do down below. I think it is advancing the timing. I am just curious about this one).

I believe the lower HAC port (not the large on on the bottom of the HAC but the smaller lower port in the diamond formation) is the HAC advancer port. Should go to the HAC port on the distributor advancer pot via a T fitting to the gas filter. There is also a little check valve that should be there as well:

You say the HAC is working and advancing properly so maybe your setup is actuating the HAC advancer on the distributor another way? Not sure there. HTH.

 

[Rocky_LC]

Thanks, Gretsch - I need to look at that.

I agree with you - it sure looks like if that port isn't hooked up, I won't get HAC advance.

Thanks -

Rocky

 

[2mbb]

If you feel like you have more power above 6000ft than below, I wouldn't say your HAC is necessarily working, but maybe the engine is just tuned for high altitude (idle mixture, timing is advanced, carburetor set up). I would expect with a properly working HAC you would have less power at 6000ft, because there is less oxygen to burn the fuel. What the HAC does is advance timing and lean out the carburetor so the fuel mixture is appropriate for less oxygen. But overall, less oxygen equals less power, not more.

 

[Rocky_LC]

Found the vacuum line and check valve off the intake manifold. It goes to the outside diaphragm of my distributor. Easy hook-up.

Thanks, all for the support!

Rocky