HACV Operation (1 Viewer)

[CurtB]

I'm assuming I have a broken HACV. At sea level, I'm getting just a bit of advance from the HAC advance port. That shouldn't happen, right?

I have everything plumbed up according to the de-smog guide, with a JimC carb and distributor.

 

[OSS]

The 2nd small diagram on the distributor should be get zero vacuum from the hose connected to it at sea level.
Once the HAC valve flips over at around 4000 ft elevation, vacuum gets applied to that diagram and it should advance the timing another 6 degrees. Nothing in between. All or nothing.

 

[CurtB]

The 2nd small diagram on the distributor should be get zero vacuum from the hose connected to it at sea level.
Once the HAC valve flips over at around 4000 ft elevation, vacuum gets applied to that diagram and it should advance the timing another 6 degrees. Nothing in between. All or nothing.

Got it. So, if I have everything connected properly, and I've checked it many times, this points to an inop HACV.

If I understand it's operation, port D, the smaller centered black port, should be "open" at sea level, so that no vacuum reaches the small diaphram.

 

[OSS]

I have a spare HAC I found in a box if you end up wanting to get another one. I purchased it used and I have no idea if it works or not. Seller said it did.

 

[OSS]

The emissions manual describes how everything works. See attached.

 

[CurtB]

I have a spare HAC I found in a box if you end up wanting to get another one. I purchased it used and I have no idea if it works or not. Seller said it did.

Thank you, sir. Now I'm not convinced it is the HAC, though.

The line to the secondary advance diaphragm goes from the intake manifold port ("filter" in the FSM), to a check valve, and to a tee. From the tee, one branch goes to the HAC port B, the other to the diaphragm. HAC port B is open at sea level (I just confirmed that there is almost no resistance when I suck on it), meaning all the vacuum should be relieved there but there is enough left to move the diaphragm. It doesn't make sense. I'm thinking maybe the tee needs to be a smaller diameter on the branch towards the distributor?

 

[OSS]

At sea level, when engine is on, the HAC valve is always sucking in some air from its bottom pipe that normally had a length of hose dangling down along the inner wheel well. It’s a small vacuum leak. (That’s been accounted for). This “bleed off” gets sucked into the gas filter fitting on the intake manifold.

At altitude, the HAC closes its internal valve and that bleed off is blocked, so the full vacuum is applied to the smaller vacuum diagram on the distributor.

The bottom of the HAC valve snaps off and there’s a polyester batting air filter stuffing inside. If that filter got totally plugged, the valve wouldn’t bleed off vacuum - so vacuum would be applied to the distributor even at sea level.

Remove the bottom of the HAC cap (it just snaps off & on) and remove the filter inside & clean it.
Then put it back together when it’s dry and try it out / see if that helped anything.

 

[CurtB]

Understood, but the strange thing happening is that, even though the port on the hac is open, enough vacuum is getting to the diaphragm to advance it a bit. If I plug the line to the hac as described in the emissions manual, I get more advance.

And, I'm getting advance vacuum even when the HAC is unplugged from the tee. I think I need to futz around with something to restrict the line between the tee and the distributor.

 

[OSS]

Well for a hack, the 2nd vacuum hose going to the 2nd vacuum diaphragm on the distributor could just be removed and plugged while you’re at sea level- then replaced once you go up into the mountains.

Doing that would be annoying (and something to forget) if you’re always driving up to the mountains, but if you’re at sea level 99% of the time, it might be worthwhile

 

[CurtB]

Well for a hack, the 2nd vacuum hose going to the 2nd vacuum diaphragm on the distributor could just be removed and plugged while you’re at sea level- then replaced once you go up into the mountains.

Doing that would be annoying (and something to forget) if you’re always driving up to the mountains, but if you’re at sea level 99% of the time, it might be worthwhile

Yep. This isn't a critical issue. I'm going to play around with restrictors to see if I can get the static advance to zero but still have the high altitude advance kick in

 

[OSS]

If the lower hose on the HAC valve is pulled off as shown in this drawing, it should completely bleed all vacuum in the HAC line through that pulled hose while engine is running and there shouldn’t be any significant vacuum pulling on the distributor diaphragm.

If that’s the case for this test, then the HAC valve inner workings are a bit clogged and aren’t letting air flow through it easily at sea level.
Check the HAC filter.

 

[2mbb]

Understood, but the strange thing happening is that, even though the port on the hac is open, enough vacuum is getting to the diaphragm to advance it a bit. If I plug the line to the hac as described in the emissions manual, I get more advance.

And, I'm getting advance vacuum even when the HAC is unplugged from the tee. I think I need to futz around with something to restrict the line between the tee and the distributor.

The "tee" you see in the emissions FSM is really a branch connection in the vacuum piping manifold for the OEM set up. This was not meant to provide a restriction. There is one flow restriction that is associated with the choke opener circuit. It is shown on the schematic as below and in real life looks like a through connector. I don't see the same symbols in the simlar diagram for the HAC. I would check to make sure your everything else in the circuit is OK and connected properly. It could be that tubing to the HAC port is clogged or collasping (tubing wall is too thin) or the filter on the bottom of the HAC is clogged

 

[CurtB]

When I pull the lower hose off of hac I'm still getting enough vacuum to advance. That is why I'm considering restricting the line to the distributor.

The line runs from the filter to the tee then to the hac and the distributor. When I pull it off the hac I still get advance.

 

[4runner2FJ60]

I deleted my HAC when desmog. I am at sea level and everything runs great. I think if you get up to altitude you can swap ports on the advancer....one being always plugged.

 

[OSS]

When I had my metal spaghetti piping off, I blew out every pipe end with compressed air. I could’ve sworn I saw debris shoot out of a few of the pipe ends.
It’s certainly not impossible for the spaghetti piping to get partially plugged in spots.