Hi all! I've read a fair few posts around the VFAD system on here, and while I like to try and understand what's going on, I've not quite hit on anything that answers my issue hence the post. Pictures seem to explain stuff best, so I'll start with one to explain whats happened.

I noticed this when topping up my oil yesterday:-

I think I'm right in thinking this is the VFAD solenoid (green connector on it). There's a hose that's snapped off it (you can see the broken bit on the solenoid on the left, and the hose up towards the belts where it's moved away).

My question is, what is the impact of this being broken off? Will it change anything?

As far as I see it, I have three options (other than the probably expensive "replace the solenoid option" ). I either leave it as it is (and tie the hose out of the way) and see what happens, plug the hole and see what happens, or try and glue it back on (and see what happens). I'd rather have a clue about what it does before I start messing around with it. From the posts I've read, it looks like leaving it off will just mean that the VFAD is open all the time - but I may well have done 2 + 2 = 5 on that one!

Any words of wisdom greatly appreciated!

 

you can remove the whole vfad. or you can replace the solenoid. gluing it won't work.

i'm not sure, but i think you should be bogging down around 6500 rpm when the vfad is suposed to open.

i have a spare if you need it. but removing the whole vfad is probably your best bet. there's a diy about it.
i think 04rx8man had the same problem.

 

the VFAD is intake nose control only

 

Cheers chaps. From the wealth of info on here, I think I've managed to piece together what will happen with that bit snapped off.

The VFAD will stay open at low revs, and the car will be a little bit noisier.

I'm basing this from looking at the vid provided by Jon316G (Troubleshooting intake valves), as applying a vacuum to the VFAD will close the second air intake port. With no vacuum applied as my bit is open to atmosphere (i.e. snapped off), it'll just be open all the time. I guess that the solenoid being open must just close the second air intake port by letting the vacuum through. In doing that, and making the car suck air through the longer intake, I guess that is the bit that keeps it quieter at lower revs.

I'll just tie the tube out of the way for now and see what happens. If anyone in the know (I've just pieced this together in a wholeheartedly amateur way!) can correct me or tell me I've got it right, please do!

 

My logic tells me gluing it back on should be easy... It's under vacuum, so the tube should be sucked onto the solenoid.

Leaving it open will result in constant "sucking" of air through the solenoid and cause the vacuum pump to work harder.... Don't think that's a good thing?

just my 2c

 

Let me clarify a couple statements here:
With vacuum in the VFAD line, the VFAD valve stays CLOSED at lower RPMs.
At 5500rpm the solenoid opens and vacuum is released, opening the VFAD valve and creating a 2nd intake air path, not a 2nd intake port (that is what the SSV does).
Now in your case if the solenoid has a broken hose/fitting, the VFAD actuator isn't receiving vacuum and the valve will stay open at all times.
But that can cause a vacuum leak above 5500rpm when the solenoid is opened (not to mention unfiltered air into your intake).

If the solenoid was kept open (which can only be done by supplying constant voltage to the solenoid) the valve would stay open.
It would be easier to just cap the nipple behind the throttle body so the valve stays open at all times.

 

Right. I'm a bit slow, so let me see if I've got this straight. This is where I've got to, and as far as I can see from replies above this is about right:

• VFAD solenoid off (no power) = vacuum path to VFAD actuator is open = actuator is actuated = second intake path closed. (apologies for confusingly referring to it as "port")
  
• VFAD solenoid on (power) = vacuum path to VFAD actuator is closed = actuator is not actuated = second intake path open.

Might have this wrong in terms of power/no power as I don't know if the solenoid is normally closed or open in terms of the vacuum path.

This bit I don't understand:
As I understand it from looking in the service manual diagrams, the vacuum is pulled via a little vacuum tank, vacuum which is provided by a pump downstream, and is isolated from the intake system. So this won't pull unfiltered air into the intake. And as far as I can make out, it's unfiltered air that's let in anyway when the vacuum is released (via some sort of nipple on the LHS of the VFAD solenoid assembly). The other side of the hose just goes to the VFAD actuator, and again is isolated from the air intake - irrespective anyway as it's in front of the air filter.

In my case, why would it cause a vacuum leak above 5500 rpm? Surely there would only be a vacuum leak below 5500 rpm when it should be pulling a vacuum but isn't. Past 5500 rpm the vacuum is shut off and as the break is past the solenoid, there's no leak.

Ideally, I just wan't it back working as it was before. I'm just wanting to check that leaving it as it is won't cause any damage.

I tend to agree with you there. It'd be the equivalent work on the vacuum pump to driving at >5500 rpm all the time (which I'd like to do, but I think the local constabulary might frown on ). I guess the other option would be to simply tape over the hole, as that should give the same sort of resistance from the normal set up.

Thanks for your replys folks, I think I'm slowly starting to get it. That said, I'm prepared to be told I'm wrong as well!

Upshot seems to be, gluing it on might work, and won't cause any damage anyway if it doesn't. myriadshalaks, I might PM you about your spare if I can't get it working ok using the half-arsed method I'm attempting.

 

Wow... I don't even know where to begin with this....

The solenoid is normally closed.
Vacuum is kept in the line to the actuator and the valve is kept closed.
Same concept as dipping a straw into liquid, putting your finger over the top of the straw, and pulling the straw out.
The fluid stays in the straw. Your finger is like the solenoid. Very basic explanation, but you get the idea.

If ever given the opportunity, take off a solenoid's housing/cover (any solenoid, not just for the RX8) and apply voltage to it.
You'll see an internal valve moving.
It can sometimes be difficult to imagine... I'll see if I have a regular air solenoid laying around I can use to show you how one works.

There are no vacuum "pumps".
Vacuum is created by the intake, which is why the VFAD is routed behind the throttle body.

When the solenoid opens at 5500rpm, the path of air (now unfiltered) feeds directly into the intake behind the throttle body.

Because that is when the solenoid's valve opens.
Below 5500rpm the solenoid is closed and there is no other way to enter the intake.

Read comment above.

Maybe I'm looking at your pic incorrectly and that's why we aren't on the same page about the solenoid.
I was thinking the break was on the actuator side.
Is the break on the actuator side or the vacuum chamber side of the solenoid?
Maybe take another pic aiming down so I can see it better.

 

Thanks for bearing with me Jon316G, I'll get it in the end. You're correct, the break is on the actuator side of the solenoid.

I've just looked at the diagram again, and and I've no idea where I got that idea from. My mistake. And I see what you mean, whenever the line to the actuator is open, and nothing's covering that hole it's taking air directly into the intake and bypassing the filter. Which I understand would universally be regarded as a "bad idea".

So when the solenoid is open (i.e. vacuum doesn't get to the actuator and second intake path is open), does it open the line at the solenoid to atmosphere completely? Or does it close the vacuum line, and open the line that goes to the actuator to atmosphere?

So, if I tape over the broken bit that pulls the vacuum (until I can find my superglue), would that suffice as a temporary fix in that it'll stop unfiltered air being pulled into the intake, and prevent (well enough) a vacuum leak?

I don't mean to sound pedantic, I just like to understand stuff.

 

The vacuum in the line is "bled" into the intake when the valve is opened.
That is why there is a one-way valve between the vacuum chamber and the upper intake manifold.
So the flow is constantly being pulled towards the engine/intake.

Instead of trying to rig/tape anything that could potentially fail, just cap the nipple behind the throttle body.
This way, no vacuum reaches the VFAD actuator and no leaks will enter into the intake.
A variety of vacuum caps can be purchased at Autozone for a couple dollars.

 

Man, this thread sounds familar :-)

 

Ok, got it. Ta for the explanation.