Conflicting/Missing info on FSM

[sdbrassfield]

Is the VTV that is in the vac line that runs to the main body of the distributor advance supposed to be Blue or Brown ? On Emmisions FSM pg 3-3 specs as blue, 3-10 specs it as brown?

Also, Where does the large hose (larger than the other 4) that leaves the HAC Valve bottom center connect ?

Help would be appreciated since the FSM does not help on this one either??

 

[2mbb]

Good question. The one on my truck is blue. The parts microfiche indicates it's part number 90925-01021 which corresponds with blue.

The large hose out the bottom of the HAC is an atmospheric vent and it does not connect to anything...

 

[Butt Ugly Chuck]

x2 That VTV is blue on mine, and hose on bottom of HAC vented to atmosphere

Butt

 

[sdbrassfield]

Thanks for the help folks. Mine is Blue also but the manual thru me for a loop. Thanks for help on the HAC...It was driving me nuts, could not find anything it would have connected to...This forum is great !

 

[hank14]

OK- here's a hijack question about the VTVs- I have 3 different ones- blue one mentioned above, green on the carb choke breaker, and another one off one of the BVSVs.

All of them allow air to pass one way but not the other.

The green one on the carb never lets the choke breaker open- does this mean it isn't working?
Aren't they supposed to slowly allow vacuum through the resistant side?

 

[2mbb]

The VTV's are not check valves. They allow flow to go both directions, but in one direction the flow is restricted to a specific flow rate (see the diagram in post 2 above--the different colors have different flow rates in the restricted direction).

(1) You need to make sure the VTV is installed in the correct orientation.
(2) if the VTV does not let any air pass in one direction then it may be bad (plugged)
(3) the choke breaker diaphragm may be broken or
(4) your vacuum port may be plugged or not pulling vacuum. Here's the test procedure for the choke breaker circuit. Go spend some quality time with your truck.

 

[sdbrassfield]

I think it should be green toward the breaker (page 3-3 in emissions fsm)...The one at the bvsv on mine looks like it is a different color, but it is a blue (021). It is apparently discolored from age/heat.

 

[hank14]

The VTV's are not check valves. They allow flow to go both directions, but in one direction the flow is restricted to a specific flow rate (see the diagram in post 2 above--the different colors have different flow rates in the restricted direction).

(1) You need to make sure the VTV is installed in the correct orientation.
(2) if the VTV does not let any air pass in one direction then it may be bad (plugged)
(3) the choke breaker diaphragm may be broken or
(4) your vacuum port may be plugged or not pulling vacuum. Here's the test procedure for the choke breaker circuit. Go spend some quality time with your truck.

I have already followed all the FSM procedures, and even switched out the VTV with a spare- it doesn't seem to move air one way nut will freely the other. The choke breaker will open and stay open if I turn it around- even after the engine is stopped. There is good vacuum from the carburetor.

I also have a brand new blue VTV from CDan for the pink BVSV. It only seems to flow one way, too. I suppose the air flow on these VTVs is restricted enough the other way that it is too slow to detect by blowing through the valve?

 

[FJ40Jim]

Scott,
The CB just needs to get vac and open as soon as the engine is running. The VTV can be left switched around to allow CB to open, then hold open after the engine is shutoff for a few minutes. In other markets and on 78-earlier USA trucks, the CB is just connected to manifold vac to operate immediately on startup.

 

[2mbb]

So the blue VTV is supposed to let through 200cc per minute. That is not very much air--it's about one cup of air in a minute. If you really want to see if air is flowing when you blow, you can connect a piece of vacuum tubing to the outlet, then submerse the other end in water. If any air flows you should see some bubbles.

Do you have a hand vacuum pump with a gauge? You could test your CB diaphragm. maybe it got a crack that allow enough air to flow such that the restricted flow from the VTV can't keep up, but unrestricted flow will pull it in. Just a though.

 

[hank14]

Thank you both for your suggestion. I'm really not too concerned about it, but in working through the emissions FSM, I am trying to understand what as well as why as much as possible- it's more interesting to me that way. Then, when I end up tearing all this smog stuff out, I will know what effect it will have.

I have not done the hand vacuum test, but will give it a try (or I may use a 60 cc syringe with a "T" to my regular vacuum gauge). I think the last time I switched the green choke breaker VTV around, the suction was still on the choke breaker and it was open when I check it the next morning. I suppose that explains that both of the green VTVs I have tried have been faulty. I may try it with the new OEM blue one just for kicks to see what happens.

 

[hank14]

Turns out both of the green VTVs were bad. I did the bubble test, and no bubbles. I bought a new one from CDan just for kicks. Now the choke breaker works as it should.

 

[Joe_E]

Interesting thread. Now I need to go do a bubble test on my original green vtv before I trust it to work on my brand new carb.
Another nice schematic there as well 2mbb.

 

[Landpimp]

I removed that VTV on my 40 and 60, Jim C(I think) said it helped preformace and I agree

Is the VTV that is in the vac line that runs to the main body of the distributor advance supposed to be Blue or Brown ? On Emmisions FSM pg 3-3 specs as blue, 3-10 specs it as brown?

Also, Where does the large hose (larger than the other 4) that leaves the HAC Valve bottom center connect ?

Help would be appreciated since the FSM does not help on this one either??

 

[Joe_E]

HA! Just performed the bubble test on the green vtv and almost popped my cheeks trying to get a bubble out. This thread definately averted a future problem there.
The blues I have were fine.