924Board.org

rcoble · Joined: 12 Mar 2005 Posts: 71 Location: Ojai California

So I got a deceleration valve (mine had been removed by PO) and I am trying to figure out where the hoses are supposed to attach. I have been looking at pictures of cars for sale trying to see where they go. No clear picture yet and both the Haynes, and the workshop manual don’t get into it other than in the line drawn diagram. I understand the diagram, but where are the hoses actually supposed to attach in the car? See this picture (not my motor):
http://www.geocities.com/proanimation/Motor-78.jpg
The blue hose in the picture is obvious but I don’t have that “Y” piece (circled in yellow) it attaches to at the air intake, and is there a small vacuum line on this as well? That would be four lines total coming into this “Y” piece. I can’t quite make it out in the picture.
Next where does the red line go? I will probably need a picture of this attachment point, I can’t see anything on that side of the car that a hose would have been attached.
Next the small control vacuum line on the bottom of the deceleration valve (not shown) I think I got that one but I’ll take advice on this as well. Anyone know what level of vacuum the valve is supposed to be set at?
Thanks
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78-924 red , my first real car at age 44.
80-928 black, bought from turbo924.
83-928 black, My current effort.

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

It's set from factory - I say leave it alone.
The red hose goes to the hard plastic connection spot between the 2 rubber boots.(it has a big yellow sticker on it in the picture)
The small vacuum hose on the bottom comes off the small tee on your brake booster line.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

rcoble · Joined: 12 Mar 2005 Posts: 71 Location: Ojai California

Well my deceleration valve isn't "set" anymore. When I got it the nut was loose and the adjuster was all the way screwed out. I just was hoping someone might know what vacuum level to set it at. I guess I could hook up the vacuum control line to the deceleration valve, and hook a vacuum switch up to one side of the valve, connect the switch to a temporary light inside the cabin, and just watch when the light comes on and adjust the valve until I think it's opening at the right moments. But I don’t have a vacuum switch and can’t seem to find one, would probably have to make one, well, I guess that would be kind of a fun project in itself!
_________________
78-924 red , my first real car at age 44.
80-928 black, bought from turbo924.
83-928 black, My current effort.

Smoothie · Posted: Sun Jun 05, 2005 4:43 am Post subject:

The decel valve's (aka- vacuum limiter) purpose in life is to prevent a sudden shut-off of airflow through the intake and the resulting vacuum spike between shifts and other times when the throttle's shut quickly. With that in mind you might be better able to get it doing what it's supposed to do. I'd think it [the decel valve] should pop open on a vacuum spike, then close more-or-less gradually, but not open at all at more normal vacuum levels like the approx 20"hg or less you'd see at idle. One clue that it's staying opened too much (or opening when it shouldn't) would be a higher idle speed. A clue that it's not opening enough or when it should would be vacuum spikes and a quick drop in rpms between shifts. When it's right, you'll see neither of the above, but will have a gradual drop in rpms between shifts.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Mon Jun 06, 2005 2:22 am Post subject:

I stumbled on something else involving the decel valve yesterday and it suggested that the adjustment is a bleed-off, affecting how long the valve stays open once it's opened. -So that screw might not have any affect on what vacuum level the valve opens at - only how long it stays opened.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

rcoble · Joined: 12 Mar 2005 Posts: 71 Location: Ojai California

Well when I mess with it out of the car, the adjuster seems to affect WHEN it opens. I am putting together a remote vacuum gauge to test it during actual driving conditions. It may take a while to find a used sensor/guage combo, but I'll post the results here.
_________________
78-924 red , my first real car at age 44.
80-928 black, bought from turbo924.
83-928 black, My current effort.

Smoothie · Posted: Tue Jun 07, 2005 4:22 am Post subject:

I wouldn't think that special testing is necessary. You should be able to tell if and how well it's working just by observing how the revs drop off when you release the throttle - and if it has any affect on the idle speed. It shouldn't affect the idle speed and revs should drop more gradually, giving a smoother transition down to idle as compared to when the decel valve wasn't installed.
Why are you installing it...emissions test requirement? -Or getting backfires or something without it?
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

There is a test for it in Haynes.
It might be easier to adjust it just so it works as the test requires.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

rcoble · Joined: 12 Mar 2005 Posts: 71 Location: Ojai California

The test in Haynes is pretty vague,.. mostly just a test to see if it is working, but not for the adjustment. I know the deceleration valve is not necessary for the car to run, although I think it should help create smoother shifting and less of a jolt when leaving it in gear and letting off the gas suddenly. I also was lucky When I went through CA smog this time, and next time I want to have everything in the car that’s supposed to be there (PO removed most of the smog equipment). In CA we must pass a visual inspection, where all original emission equipment must be installed and working to pass, even if the car meets the numbers without it.
But really that’s just an excuse for me to futz with and tinker with something else on the car, as I’ve got the rest of it done and dialed in.
My 928 is the car I'm going to use for performance, and the 924 is my legal eagle.
_________________
78-924 red , my first real car at age 44.
80-928 black, bought from turbo924.
83-928 black, My current effort.