Spark & Air Flow Question.
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TECH Resident
Joined: Aug 2003
Posts: 970
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From: England UK
Spark & Air Flow Question. I'm trying to learn more about the spark advance. When we go WOT we want to try to get as much air into the engine as possible and matching it with the right amount of fuel. So to get more air in we advance the timing until it knocks then back of a couple of degrees, we then know got the best we can get. In my case WOT is at 28 degrees around 3600 RPM+.
So in the case of WOT we advance the timing to increase air flow.
Now on Idle, I wanted to make the car use less fuel on Idle. The idea was if I create less air flow I can then put in less fuel. Of course there is a limit to how little air you can flow until it stalls.
My Idle spark was 21 degrees. My air flow was 0.80lb/min, I would assume you decrease the timing to create less air flow as it would e the oppersite to WOT, degreese all the way to 0 degrees eventually, the tone of the engine changed, didn't note the Air flow reading but noticed my injector duty cycle increased. So this was the wrong direction to go. I then went from 21 degrees up to 40 degrees spark advance, noticed my Air flow went from 0.80lm/min right down to 0.52lb/min. My IAC was down to 0. So this was too far to go. Have settled on 38 degrees for now, idles great, better than 8% fuel saving on idle.
So my question is, at WOT we increase timing to suck in more air. On idle we increase timing to suck in less air.
Why?
So in the case of WOT we advance the timing to increase air flow.
Now on Idle, I wanted to make the car use less fuel on Idle. The idea was if I create less air flow I can then put in less fuel. Of course there is a limit to how little air you can flow until it stalls.
My Idle spark was 21 degrees. My air flow was 0.80lb/min, I would assume you decrease the timing to create less air flow as it would e the oppersite to WOT, degreese all the way to 0 degrees eventually, the tone of the engine changed, didn't note the Air flow reading but noticed my injector duty cycle increased. So this was the wrong direction to go. I then went from 21 degrees up to 40 degrees spark advance, noticed my Air flow went from 0.80lm/min right down to 0.52lb/min. My IAC was down to 0. So this was too far to go. Have settled on 38 degrees for now, idles great, better than 8% fuel saving on idle.
So my question is, at WOT we increase timing to suck in more air. On idle we increase timing to suck in less air.
Why? 
