VCV Valve Operation

[mwebfj60]

Is it correct to say that the vacuum applied to the VCV valve just allows the other ports to flow air and no vacuum actually travels through the valve? For instance, if I was checking my passenger side VCV valve, I can put a mighty vac onto the vacuum port and it should just hold pressure?

Since this valve just vents the dizzy can it be removed and the dizzy simply hooked to the air cleaner? I do believe mine is busted and $40 for a used replacement is a bit steep.

 

[Kynot62]

If its anything like a 62 I do believe there is air flow going through the cap. It pulls air from inside the cab and helps dry out the inside of the dizzy. If you look there is a hose going to the fire wall below the glove box. This is the intake for the dry air and then it goes to the air cleaner. This is what creates the flow. Why it is controlled by a VCV I don't know but someone somewhere had a reason for it.

Tony

 

[mwebfj60]

Thanks Tony. Yes, it's the same, one hose from the firewall to cap, the other from the cap to the VCV, from VCV to air cleaner and another from VCV to manifold vacuum. The only thing I can think of is possibly not wanting moist air getting into the cap when the motor isn't running? Who knows? I was hoping someone here had a definitive answer on the reasoning.

 

[Vandyfan]

My fj62, 3FE, just started running like crap and has all the signs of being vacuum related. While poking around at vacuum hoses, I noticed what I think is the VCV (directly above the "canister") had a small nipple with no hose connected. The only hoses I found dangling loose come from the firewall around the glove box area and one that Ts off the transmission dip stick tube. Looking at my vacuum hose diagram it appears this nipple should be connected to the air cleaner since the 2 going to the throttle body are connected. You refer to the firewall hose going to the "cap" (I assume distributor cap). I'm having a hard time because I could see a hose developing a leak or coming loose, but now it seems they weren't routed correctly beforehand.

 

[Vandyfan]

In an attempt to better explain what I currently have vacuum hose wise: I have 2 hoses going from the air cleaner to the distributor cap and 1 going from the air cleaner to the throttle body, I have 2 hoses going from the vcv to the throttle body, 1 hose from vcv to the canister, and 1 unconnected nipple on the vcv, I also have the hose from the firewall dangling free

 

[mattressking]

From my understanding of the valve, the vacuum opens the diaphragm so air (atmospheric) can pass through the valve into the air cleaner. Once the engine is shut off it, vacuum disappears and the valve shuts.

In my mind this keeps the distributor sealed when not running and only opens the distributor cap to vent when running.

To me the only difference between having the valve and not having it is the possibility of humidity trickling in through the intake down the hose into the cap...A long shot but if stored outside more likely to have corrosion/rust/dirt.

 

[mwebfj60]

This thread breaks it down pretty good.

The VCV

 

[Vandyfan]

That is a very thorough breakdown of how it works. Thank you for the time and effort. It seems the vcv is an almost insignificant piece of the vacuum puzzle though. Also, with my 3FE plumbed correctly it is still running like crap all of the sudden.

 

[LAMBCRUSHER]

VCVs can go bad and leak internally. they are the devil to suss out. test it for serviceability. other things that can make the fj62 idle like poo, are any type of intake leak...oil fill cap, dipstick, PCV tract, VC gasket, and most importantly, the main intake duct and ISC valve intake duct. any cracks in that, and you're gunna need some gorilla tape.