Disable Decel Valve

[jrwilson]

While I continue to try and diagnose my car's engine issues, it developed a fun stall when putting the clutch in coming to a stop, so I'd like to just remove the DV from the equation.

I understand capping the top vacuum line, but what do I do with the bottom one? Mine seems to have a weird T connector on it that vents to atmosphere and I'm wondering if I just leave it like that or am I capping something else off?

Yes, I know I need to check my pressures (tested high spec, rebuilt WUR coming soon) and whatnot. Just want to know what to do with the hoses going to the DV.

[jrwilson]

Here's a shot of the weird T to atmo. Plugging it makes the engine die when you rev.

[proporsche]

did you try to adjust it? ..if it is too close the car could die ..open it up by screwing the 6-7 mm tube
1st loose the 13mm wrench nut

Ivan

[jrwilson]

It was adjusted to open around 19Hg and it's maxed out in terms of screw threads. It was used when I got it and it may have finally fully failed. So, I want to try and remove it for now. Just need to know what to do with the lower hoses - cap or not?

[David Inc.]

Mine's an '82 so it's a different piece with the same function, but there should not be a vent to atmosphere there...

https://jimsbasementworkshop.com/CIS/pages/air_vaclines.html

It's #9 in this diagram, look at the connections.

Edit: For the pre-80 car it looks like there shouldn't be a T, and disconnecting vacuum from the top port would be all you need to do. Take vacuum off and it won't open the valve for the throttle bypass. Definitely shouldn't be an opening to atmosphere anywhere.

[proporsche]

do not know what is 19hg but from the look of it it is way too close..
ivan

[jrwilson]

I've gone over that diagram plenty, just not sure because of the line you see in my photo that comes out of the black aluminum T at the bottom of the DV.

[jrwilson]

Originally Posted by proporsche

do not know what is 19hg but from the look of it it is way too close..

I meant that it was opening when I applied 19Hg of vacuum to the top. Which is slightly below spec, and the adjustment was maxed out.

I'll re-test it but in the meantime to address the stall when letting off the throttle I'd like to take it out.

[David Inc.]

Originally Posted by jrwilson

I've gone over that diagram plenty, just not sure because of the line you see in my photo that comes out of the black aluminum T at the bottom of the DV.

I don't think that should be there... Where do the two lines go? And is there another port coming out of the DV perpendicular to the body on the backside?

Edit: I might be totally off-base, I don't know pre-lambda SC, but that doesn't look right for what I understand of it.

[proporsche]

this image should also help you.

[jrwilson]

Yes that photo is very helpful. Do I just connect the two bigger lines together?

I have no idea what the T part on mine is, it came that way.

[proporsche]

hard to see what you got there ,just get rid of the T and connected it as david diagram ...and the pic i have sent you

ivan

[David Inc.]

No that would be a permanent throttle bypass. If you want to remove the valve entirely then you should cap the big ports on the throttle body that it connects to (or should connect to). Otherwise yeah, as Ivan says return it to stock. Somebody did something weird with it so who knows. Can you get a photo of where those lines are going, and if the perpendicular port on the DV is connected to anything? Now I'm just curious.

[jrwilson]

Okay, caps it is. Thanks!

[SkiVT]

Might have been to cruise control at some point. Hard to tell what happened but as you say, doesn’t really matter if you remove the DV.

[jrwilson]

Okay, that is also super helpful, thanks!

For future reference, that vacuum line goes to the cruise control valve - there's two lines, a bigger one and behind it, a smaller one.

[boyt911sc]

Jeremy,

The decel valve you have now is better than the previous one you had before. Unfortunately it was opening at 19” Hg compared to the ZERO vacuum before. It might have failed too. As soon as I get back on my feet, I will finish the calibration of your WUR and include a decel valve. I was experiencing some dizziness but feeling much better today.

If you want to disable the decel valve, simply plug the 2 big braided hoses but do not connect them. And connect the small vacuum line for the thermo valve directly to the throttle body.

Tony

[jrwilson]

Great, thanks Tony. Feel better soon!

[jrwilson]

Okay, this is super weird - I disconnected the DV as suggested above, but I also plugged that line from the bottom of it into the cruise valve and once the car gets warm, it dies immediately and I can't restart it. Unplug that line, the car now runs better than it's ever run.

Shouldn't that line be an air leak?