Negatives to high timing at idle?
08-22-2012, 10:02 AM
#1
Negatives to high timing at idle? So I really haven't been overly compelled to mess with this since the car seems to run fine but I am curious.
At idle, my car likes to run a lot of timing. Usually in the mid 20s and more if cold start (26-28*). It drives great and everything though. The last time I tried to pull some or play with the controls in EFI live it seemed to run worse with less. I recall setting several of the tables to lower values but the PCM was adding more from somewhere and I never did really nail down where.
Is there any negative to having more timing at idle? I know I used to run around 18* when carbed.
At idle, my car likes to run a lot of timing. Usually in the mid 20s and more if cold start (26-28*). It drives great and everything though. The last time I tried to pull some or play with the controls in EFI live it seemed to run worse with less. I recall setting several of the tables to lower values but the PCM was adding more from somewhere and I never did really nail down where.
Is there any negative to having more timing at idle? I know I used to run around 18* when carbed.
08-22-2012, 10:15 AM
#2
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If it's adding timing and you don't know from where most likely the pcm is using the underspeed table and adding timing to bring the idle up to it's set speed. Much faster for the pcm to alter idle speed by adding or pulling timing then with the idle air motor.
I personally like running alot of timing at idle, I don't know if it's correct but I do it.
I personally like running alot of timing at idle, I don't know if it's correct but I do it.
08-22-2012, 10:40 AM
#3
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If your timing is too high, then there will be a point where
the adaptive spark might get "upside down" (more timing
from that puts you past MBT) and you get less RPM rather
than more, leading to an unstable RPM-control-loop.
Your maximum net timing should be somewhere that still
has upside, and this is base plus adaptive range plus any
active adders; determine the best timing and then subtract
the "peripheral" stuff for the base.
the adaptive spark might get "upside down" (more timing
from that puts you past MBT) and you get less RPM rather
than more, leading to an unstable RPM-control-loop.
Your maximum net timing should be somewhere that still
has upside, and this is base plus adaptive range plus any
active adders; determine the best timing and then subtract
the "peripheral" stuff for the base.
08-22-2012, 11:41 AM
#4
In a roundabout way that's kind of how I ended up where I'm at with it. I used the EFI live bi-directionals to hunt for the timing which let the car idle properly without hunting and had it set that way in the tables. Later I went back and reduced those in that table but the car continued to see those for total timing.
As long as there is nothing wrong with it, I won't feel bad leaving it alone. I've just got the rest of my tune so that I'm fairly happy with it and would like to go back and clean up any rookie mistakes that might be present.
As long as there is nothing wrong with it, I won't feel bad leaving it alone. I've just got the rest of my tune so that I'm fairly happy with it and would like to go back and clean up any rookie mistakes that might be present.
