Chasing a vacuum leak

[OSS]

So are you saying that on a new valve, air can flow from Z and out X when there's no vacuum on S?
If that's the case, I'm the moron and I'll delete my previous post. Because if X flows to Z when there's no vacuum, then gasoline fumes can flow down Y to X to Z and down into the distributor if the hoses are routed according to the FSM. !

 

[mwebfj60]

So are you saying that on a new valve, air can flow from Z and out X when there's no vacuum on S?
If that's the case, I'm the moron and I'll delete my previous post. Because if X flows to Z when there's no vacuum, then gasoline fumes can flow down Y to X to Z and down into the distributor if the hoses are routed according to the FSM. !

That was what brought me to tear down the VCV, and I can't say with complete confidence either way. It doesn't seem to me that it could seal but if it was designed to leak X to Z then why do you even need X? Your diaghragm pressure would just relieve through Z.
If they are separate from each other new,than you are completely right with what you posted.
Either way, putting a T from X to whichever line you have coming from the distributor or the air cleaner is going to expose the X chamber (back of the diaghragm) to Ozone or Gas vapor.
I think we have over thought this by just a little. It doesn't help that there are conflicting things in black and white though. I like the detective work and logical conclusion you came to about the failing VCV. Good stuff. Cheers

 

[NeverGiveUpYota]

Ok so which is it guys @OSS and @mwebfj60? Who's gonna toss $80 (I did get mine for $66 but that was when adifferent guy was working at my dealership) in the garbage for dissect?

 

[OSS]

I have a new blue VCV I just tested. And @mwebfj60 you're right!
There is a slow leak between Z and X along the internal valve rod as I guess there needs to be since the rod/plunger needs to slide up & down.

SO THAT BEING THE CASE>

My previous post was wrong and I'll edit it. It is MUCH more important to completely seal off the distributor from the air cleaner housing than attempt to keep ozone away from the diaphragm.

So, although the FSM schematic is wrong, Toyota did connect the hoses correctly. X & Z should be teed together and only Y should lead up to the air cleaner housing.

As far as the distributor vent VCV is concerned, it should be considered a wear item and should be checked occasionally to make sure it's working properly. Wow!

 

[chichiflys]

MWEB - but if there is no vacuum on the VCV it is because the engine isn't running, right? And thus if the engine isn't running then there wouldn't be any ozone being produced in the dizzy and so wouldn't be damaging the VCV? Or am I too many beers into this?

 

[mwebfj60]

....

Does anyone use teflon when installing the gas filter? My assumption is that if Toyota wanted additional sealant, it would be pre-applied or noted somewhere in the fsm.

Back to our regular scheduled program....

I recently did some Natural Gas plumbing at my house and the plumber said no thread sealant on tapered threads, just sealant on non tapered threads. Makes sense.
After my gas filter was screwed in, I put some loctite around the threads where it meets the intake. I also put a small bead of loctite around the gas filter ring where the metal meets the plastic. I had a couple at the time that had a real slight leak around that seam.

 

[mwebfj60]

MWEB - but if there is no vacuum on the VCV it is because the engine isn't running, right? And thus if the engine isn't running then there wouldn't be any ozone being produced in the dizzy and so wouldn't be damaging the VCV? Or am I too many beers into this?

Right. You would still have some residual vapor trapped and I think that's what OSS was concluding that over time, that Ozone is eating the diaghragm in the VCV causing it to fail faster than the evap VCV.

 

[mattressking]

Awesome diagram. Can you share the link to that parts manual — PLEASE? I’d love to have that in higher res to print it out.

Thanks so much.

Back to our regular scheduled program....

I recently did some Natural Gas plumbing at my house and the plumber said no thread sealant on tapered threads, just sealant on non tapered threads. Makes sense.
After my gas filter was screwed in, I put some loctite around the threads where it meets the intake. I also put a small bead of loctite around the gas filter ring where the metal meets the plastic. I had a couple at the time that had a real slight leak around that seam.

Good to hear, I didn't think anything was needed for tapered fittings and high temps to me would make teflon superfluous. Always nice to get some extra reinforcement from others.

I went with a new gas filter, so no extra work needed

 

[Spike Strip]

This stuff gives me a headache.

This one is perhaps easier to decipher.

But my questions to you all is couldn't one just run a hose with a check-valve from Air Cleaner straight to the distributor and eliminate all the other plumbing ? Yes, I'm sure there's temp controlled vacuum on the VCV, but how could eliminating that hurt emissions (when fully warm engine)?

 

[OSS]

Brand new machined shiny metal tapered fittings may not need thread sealant when mated to brand new machined threads, but nothing on our truck is brand new shiny metal. Everything has been corroded a bit. Take the rear heater riser pipe off the back of the head for example. That's a tapered thread, but it will absolutely leak unless a high quality high temp liquid thread sealer is used on it.

Also anything screwing into aluminum should have some sort of thread dressing, otherwise the steel will corrode & gall inside the threads - causing the fitting to possibly seize & break off when removal is attempted years down the line.

 

[mwebfj60]

I normally use this for threads

 

[mwebfj60]

This stuff gives me a headache.

This one is perhaps easier to decipher.

But my questions to you all is couldn't one just run a hose with a check-valve from Air Cleaner straight to the distributor and eliminate all the other plumbing ? Yes, I'm sure there's temp controlled vacuum on the VCV, but how could eliminating that hurt emissions (when fully warm engine)?


View attachment 1561805

Nice diagram.
Interesting thought about deleting the VCV and running a one way valve.

 

[Spike Strip]

That anti-seize is great for sensors that need to maintain a good ground.

For plugs and water jacket, etc. this stuff is the awesome sauce:

 

[4Cruisers]

Looks like I'll be switching my hoses around so "Y" goes directly to the air cleaner.

 

[Dclowd9901]

Got my shovel and I’m gonna resurrect this thread from the rotted grave in which it was... rotting.

Quick question: is there supposed to be any vacuum off of the air cleaner housing? There’s like 5 vacuum lines off of it, so I’d _think_ so, but ... you know what they say about assuming.