#1  
Old 05-12-2022, 04:36 PM
Hokie1984 Hokie1984 is offline
Senior Member
 
Join Date: Sep 2017
Location: Blacksburg, VA
Posts: 124
Default Ported v. Manifold Vacuum for distributor

I know this has been discussed before, but I am struggling to get my timing set. I thought I slipped the outer ring on my harmonic balancer, but that looks fine (thank you Jeff). Anyways, I am setting up my new EFI using the ported vacuum for the distributer and it just doesn't respond correct. It tells you to set the timing at 5 degrees with the vacuum disconnected. I am questioning why you would need to disconnect the ported vacuum because at idle it is effectively 0 inHg meaning it really has no impact on the advance. I checked the ported vacuum and sure enough it you rev it up, it defiantly actuates.

I looked in the shop manual, and it is silent on which vacuum source to use on non-AIR L6 cars. Interestingly, on V8 cars it says "The vacuum advance is connected directly to manifold vacuum so there is full vacuum advance at idle." So I am questioning, should I also connect to full manifold vacuum. I don't remember how much vacuum existed on my Quadrajet but I do recall the timing shifting a bit when it was disconnected. Any ideas?

  #2  
Old 05-12-2022, 05:33 PM
sprintbird sprintbird is offline
Senior Chief
 
Join Date: Feb 2002
Location: Anna, OH
Posts: 368
Default

Your mistake is following the initial timing indicated in the Pontiac manual. Gasoline is completely different today than in 1966. You want to be 5 to 7 degrees on top the 5 before TDC. So 10 to 12 degrees before top dead center is a good starting point. Don’t switch vacuum sources just yet. See if your EFI likes that much better.

  #3  
Old 05-12-2022, 07:44 PM
Hokie1984 Hokie1984 is offline
Senior Member
 
Join Date: Sep 2017
Location: Blacksburg, VA
Posts: 124
Default

Ok that makes me feel much better. I am 12 to 15 degrees currently and it runs infinitely better. At that timing my vacuum is good and it runs much smoother. I am still letting the EFI learn at this level before I start tweaking the accelerator pump settings.

  #4  
Old 05-12-2022, 08:41 PM
sprintbird sprintbird is offline
Senior Chief
 
Join Date: Feb 2002
Location: Anna, OH
Posts: 368
Default

Great to hear! You are on your way then. Good luck!

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 12:07 AM.

 

About Us

The PY Online Forums is the largest online gathering of Pontiac enthusiasts anywhere in the world. Founded in 1991, it was also the first online forum for people to gather and talk about their Pontiacs. Since then, it has become the mecca of Pontiac technical data and knowledge that no other place can surpass.

 




Copyright © 2017