I have been tuning my 6E motor for about 6 months now and am just starting to get close to trouble free operation. One question keeps poping into my head though...

I am running the zz4 cam with 1.6 rr in my little 305 (tpi) and it has certainly changed the behavior quite a bit from the peanut cam I had in there. Now getting a smooth idle is very difficult and I was thinking that with more overlap the O2 threshold rich/lean point should change. the question is which way.

I figure with more overlap at idle, more of the intake charge on average would go by the O2 sensor per pulse from each cylinder so this would lead me to belive I need to lower the O2 constants to get 14.7 in the chamber at ignition.

Sound right?

 

so no one wants to take a shot at this topic?

I thought for sure someone would have changed their O2 cross point to make the computer control to what the engine really needs...

 

If u did a you would have found at least one post concerning it in the stickies and there are several more around.

For an example, here is one from the "Tuning FAQ" at the top of the board.

https://www.thirdgen.org/techbb2/sho...ghlight=afs+74

later
Jeremy

 

Well Jeremy, I have done searches in the past and have read this thread many times including today where I found that you yourself do not seem to understand the answer to my question either.

Someone care to break down and explain the o2 constants to shed some lite on them?

Goofed with them a few times using the romulator b ut never quite figured them out or which would work most for my benefit

thanks
Jeremy

This issue in my head is far from resolved in the existing threads and I for one would like to start additional dialogue.

I have disabled AIR on my rig but I seem to still have trouble getting a smooth idle quality. I also get a good bit of eye watering stink with extended idling.

I of course will "goof with" the O2 threshold and min max values as you have done -- I was only asking if there were more learned opinions out there like trax, that could give more definitive (read quantitative) suggestions...

 

FWIW, idle problems may result from either mechanical or control issues.

A brief technical discussion of GM control parameters is found here, with some
additional reference material:
http://www.454ss.com/cgi-bin/2004for...num=1081825382

 

This is one of the papers written a while ago on the 747.
Very good reading and should ansew most if not all of your questions regarding the o2.
http://www.diy-efi.org/gmecm/papers/747fuel.txt
There are several others there worth reading as well.

 

cool thanks for the input.

 

its not exactly what you have asked about, but i have had some success fixing this condition by increasing spark advance at idle. try it and see if it helps.
ben.

 

Yes I have tried that. I have about 25 degrees now but have tried even more with no success curing a slight hunting condition and what feels like intermittent missing.

 

Try moving your O2 threshold up.
I have my "Closed loop rich/lean threshold Vs airflow" set to 747mv for 8 grams/sec MAF flow.
I was having a rough idle issue and what felt like an intermittent miss. My WBo2 was showing my AFR at ~15.5-1...
Now it's abt 14.0-1 and seems much happier.