Do I need this? (cycle valve)
 

Do I need to retain the cycle valve? (circled below)

http://forums.pelicanparts.com/uploa...1233053556.jpg

It is in a fuel line that runs between two ports of the fuel distributor and the valve itself has an electrical connection.
I am about to replace my FD with one that has port A plugged, so obviously the valve isn't required for all engines.
PET shows that it is used on 68/930 engines only (which mine is).
I have already gone to a Leask WUR and deleted a few other various valves.

Can I just delete the valve and hose?
What is its purpose in life?

Come on, don't be shy.
Surely someone out here knows what this thing does?

Frequency valve . Used for closed loop operation. Connects to ECI under seat . If you run open loop that device will not be doing anything since it has no voltage source to operate and influence control pressure

Just a little thread hijack here: I am running open loop (i.e, unplugged the O2 sensor, but left the frequency valve connected electrically). I suspect that the valve has defaulted to some set duty cycle as a result. Correct? I wonder if I shouldn't finish the open loop setup by disconnecing the freq. valve as well.

And, I wonder if the valve may be causing the periodic very slight leaning that I see on my AFR when at steady non-boost throttle position. This just recently showed up (the slight leaning). Could it be that the valve is starting to show some problems (as in the cycle reducing or the valve plugging up) - leading to a momentary lean condition? Doesn't this valve re-direct fuel pressure from the distributor back to the tank, thus changing the mixture under normal closed-loop operation?

I want to say I still have mine, but I have removed my O2 sensor and all electronics under the seat. If I'm not mistaken, I had to reroute the fuel line when I installed the IA modified fuel head.

Who knows what it's doing now.

my understanding is that it effects the control pressure and thus the main piston valve movement of the fuel distributor.. the secondary effect of the control pressure change is the gas return as you said...If the ECU is still connected to the harness then control voltage will be applied... with the O2 sensor disconnected the ecu settings will probably inject a pre-set default voltage or duty cycle . I am not sure if it will vary over load though...

I think it is nothing more than a Bosch electronic fuel injector...like a cold start valve...

Thanks guys.
From what I can deduce, it is only fitted to US cars, so all others get by without it.
If it works in conjunction with the narrow band O2 sensor, I think it's about to rekindle that relationship up in the big box in the attick. :)

At least in the NA cars the frequency valve will default to a 50% duty cycle (i.e. neither rich nor lean), so in theory should have no effect if in open loop mode.

You're absolutely right on the default at something like 50% duty, which to me says that in open loop it's always at a constant cycle and therefore a consistent affect on the control pressure. But...and here's the but.....if it should begin to fail (say, not letting any fuel at all go through it), then the control pressure would go up accordingly and your mixture would move toward the lean side. Or vice versa, should the valve stick open and the pressure drops, then suddenly you would be over rich.

That's why I asked the question early on in my thread hijack. My valve is still back there just happily duty-cycling away in open loop, but someday it may fail, or is currently beginning to fail (intermittently operating or plugging) and causing periodic lean conditions.

Just a theory....it could be something else like a fuel injector plugging just enough to show a little lean on my AFR. Or or or or....who the hell knows, just another mystery to figure out.

Hey Jim. So did you just run a fuel line to the upper and lower chambers in the dist and leave the F-valve out?

To be honest, I'd have to look again at what I did. When I got the modded fuel head back, the port configuration was a little different and I had to re-rout a line and remove one. I'll see what pics I have of it before and after.

the bosch book i have says the FV controls the pressure in the lower chamber. is this the same for the 930?

when you go on boost, does the FV lower the pressure to richen the mixture, or is that done by the WUR with a vacuum circuit?

if you remove the FV, would you block it off or put in a straight thru line? what ever is done, i would think the WUR CP would need to be changed.

I have the Imagine Auto fuel head on mine, and the Lambda fuel ports on the head are not used. Mine came with a threaded plug fitted in location "A" of your picture. Thus I'm no longer running it and removed it. Even before going to the modified fuel head, the O2 sensor was disconnected, so I doubt it served much of a purpose.

The FV is in a loop on the fuel dist from location "A" to location "B" which is not defined in the picture. If you plugged location "A", shouldn't you also have to plug location "B".

At "B" there are two hoses connected to the FD with banjo fittings - one from FV and one to WUR.
If the FV is deleted along with its hoses, the port at "A" is plugged and the short banjo bolt used at "A" can be used to connect the single hose to WUR at "B".

I have also found more info on this valve in the Bentley manual Bosch Fuel Injection & Engine Management. This basically explains what it does and how it does it.
I have copied the relevant paragraphs below for those looking for more info.

http://forums.pelicanparts.com/uploa...1233200708.jpg

]http://forums.pelicanparts.com/uploa...1233201100.jpg

[img]http://forums.pelicanparts.com/uploads14/lambda+0061233201008.jpg[/img

(Ignore the graphics)

This is all you need:

http://forums.pelicanparts.com/uploa...1233209238.jpg

That's a euro dist, correct? I thought they do not have a FV?

I've pretty much ditched it all except for the WUR, fuel head, and cold start valve. The AAR, AAV ,and Lambda frequency valve are long gone.

And that brings me to my next question - APOLOGIES FOR GOING OFF TOPIC - can you eliminate the cold start valve? Mine is still working, but I think it's an expensive replacement. Just wondering. One day, I'm sure it will fail. Just curious if you can live without it.

If you live in a warm climate you can eleminate the CSV. There are a couple folks here on the board that have done so.