Show full size 924Board.org
Discussion Forum of 924.org
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 Technical FAQ924 FAQ (Technical)   Technical924 Technical Section   Jump to 924.org924.org   Jump to PCA 924 Registry924 Registry

popping on decel - decel valve ?

 
Post new topic   Reply to topic    924Board.org Forum Index -> General Discussions
View previous topic :: View next topic  
Author Message
foxtg557  



Joined: 05 Aug 2007
Posts: 99
Location: Hamilton On
PostPosted: Thu Aug 14, 2008 10:57 am    Post subject: popping on decel - decel valve ? Reply with quote
My car is driving / idling very very well. A little while ago I was describing some popping back I was getting, Smoothie suggested the Decel valve. I noted that my car didn't have a decel valve at all. I just got one and installed it.

Ran from the top of the decel valve to the " Y " piece that connects the AAV valve, the Decel valve both to the throttle body. From the side of the decel valve I connected that to a pipe sticking out of the side of the intake boot. Off the bottom of the decel valve I connected that to the break booster vac line.

I got this set up, excited to see if I was still sounding like a machine gun while decel'ing. Unfortunately I still sound like a machine gun (popping back) while deceling from high rpm's (First gear 5000 rpms, let off the accelerator, and i get pop pop pop pop really fast...)

Any thoughts?
Thanks
Dave.
_________________
77 924, It Drives !
Back to top
View user's profile Send private message Send e-mail MSN Messenger
Min  



Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
PostPosted: Thu Aug 14, 2008 12:33 pm    Post subject: Reply with quote
The popping noise your hearing is fuel and air mixing in your exhaust and then igniting. I honestly don't know how to fix that issue on a CIS car though. It can be caused by a variety of things though, chances are your running a bit rich just before the popping occurs. Check for vacuum leaks and then check your fuel system out.

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.
Back to top
View user's profile Send private message Send e-mail AIM Address Yahoo Messenger MSN Messenger
Smoothie  



Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
PostPosted: Thu Aug 14, 2008 2:55 pm    Post subject: Re: popping on decel - decel valve ? Reply with quote
foxtg557 wrote:
sound like a machine gun (popping back) while deceling from high rpm's (First gear 5000 rpms, let off the accelerator, and i get pop pop pop pop really fast...)

The problem, as Min alluded to is a too rich mixture that's burning in the exhaust. It happens on decelleration because the throttle shuts quickly, cutting off the air supply, but fuel delivery is not cut so fast (therefor the temporarily overly rich A:F mix). The decel valve deals with the problem by opening an air path that bypasses the closed throttle valve. The small control line to the decel valve is attached to a manifold vacuum source (meaning somewhere downstream of the throttle valve). When vacuum spikes as the throttle shuts, the decel valve is pulled open by vacuum through that small control line. The two larger decel valve lines provide the air path. One of them needs to be connected to provide an unobstructed air path from upstream of the throttle valve, and the other large line needs to lead to an unobstructed port on the intake manifold (downstream of the throttle valve).
I'd double check the line routing (it probably matters which port of the decel valve goes upstream and which goes downstrem, so if it's correct otherwise, try swapping the large line connections).
If your connections are correct, next thing to suspect is the decel valve itself.
_________________
"..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
Back to top
View user's profile Send private message Visit poster's website
foxtg557  



Joined: 05 Aug 2007
Posts: 99
Location: Hamilton On
PostPosted: Fri Aug 15, 2008 10:47 am    Post subject: Reply with quote
Thank you Smoothie, i'll continue tinkering with the valve line routing and post results.
_________________
77 924, It Drives !
Back to top
View user's profile Send private message Send e-mail MSN Messenger
foxtg557  



Joined: 05 Aug 2007
Posts: 99
Location: Hamilton On
PostPosted: Sun Aug 17, 2008 5:32 am    Post subject: Reply with quote
So I believe I have my vacuum limiter working properly, but I am still popping on deceleration.

I left the vacuum line routing the way I had initially described, this seems to make the most sense. With the car idling and me feeling when and where I get vacuum off the limiter by pulling lines, sure enough when I rev the engine, with a thumb on one of the large ports on the limiter, when I let the engine rev down I can feel the limiter open up and begin sucking air towards the intake manifold... seems to be functioning properly, thus i'm slightly confused.
_________________
77 924, It Drives !
Back to top
View user's profile Send private message Send e-mail MSN Messenger
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> General Discussions All times are GMT + 10 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group