AB Valve Question

[Richie G]

Working my way through the engine bay and starting to take apart and get ready for some work replacing the mess of hoses left by PO.  I took the AB valve and corresponding hose off and a bunch of what i would say looks like petrified carbon fell out.  Some of it is typical dust and small particles but a few are large and pretty "square" so I'm wondering if this is some sort of broken diaphragm, or gasket or something in there?  Or is it just carbon that formed this way?  Last i had the car running about 6 months ago I don't recall any backfire, how would I know if this valve is still good?  Or is there a way to disassemble and clean it?

BTW search seems to be down so i couldn't get anywhere.

[Zed Head]

Probably just me, but what the heck is an AB valve?  Anti-backifire?  Not seen one on an L6.  Are you working on a different engine?

[Richie G]

anti backfire yes 71 240z stock engine 

[w3wilkes]

Just plug this into your Google search bar and add what you want to search for after a space at the end;

site classiczcars.com

I find I get better results with this search than the forum search box.

[w3wilkes]

And which one of these 3 almost duplicate threads are you going to stick to??

[Richie G]

This one. Whatever was going on that night with search also kept giving me a response that my post was missing required information so I might have hit submit a few times I tried to go back and edit and delete post but I guess only administrators can do that.

[dutchzcarguy]

8 hours ago, Richie G said:

I tried to go back and edit and delete post

But you CAN make them invisable, there is a button somwhere to make them invisable. 

[dutchzcarguy]

BTW,, never seen/had a AB Valve.. they are typical a USA delivered 240z part..  It's not on my euro engined 240z.

[Richie G]

Wondering if someone can answer / confirm this for me.  I just received a valve from a pick and pull that looked like it was in really good shape.  It needs some cleaning up but no rattle inside.  What's interesting is that the difference I see is that air freely flows through the valve when i blow through it where as the one i took off the car you can't at all.  So it got me thinking, this valve as described in what material i could find operates by allowing secondary air in to lean the mixture out when you suddenly release the throttle

"When the throttle is released intake manifold pressure falls, and through a small hose connection to the gulp valve, this vacuum causes the gulp valve to open. This allows air from the air pump to enter the intake manifold and lean out the fuel/air mixture, preventing backfiring"

And in looking at this diagram i found, seems to confirm that

So with that said, would it make sense that the valve should stay "open" for air to pass through when no vacuum is applied at all, meaning i have it out of the car.  I would think so right?  if a drop in pressure allows the secondary air in then I would think the "at rest state" of the valve is fully open if no pressure when fully disconnected is present.  That would mean the one I just received probably is good right?  I'm a few weeks away from even installing and firing up for the first time to really tell.

 

Edited July 11 by Richie G
Correct picture

[Patcon]

Yes, that sounds right. Do you have a way to apply vacuum to the little port?

[Richie G]

I might Maybe one of the attachments from a brake bleeder kit I have might fit and I think I can hand pump some vacuum there I'll try in a little bit and report back good idea.

[Richie G]

@Patcon good news bad news i think.  So first i tested the old one that had the pieces fall out and has some rattle.  wont hold vacuum at all so i think that convinces me that one is trash.  the "new" one I was able to find a fitting and pump to 25mmhg and it holds for quite a bit.  that's the good news.  the bad news is the valve doesnt seem to change, still easily blows through it.  So either the valve is stuck open or maybe i need more pressure i can't generate?  does 25mmhg match what one would expect under normal driving conditions? assuming this is enough pressure, any idea what would be a safe way to try and get the valve moving again?