Tough LS1 PCM question, let's see who can get it?
02-26-2004, 04:40 PM
#21
On The Tree
Ok, this is how I got here,
A refresher for those that already know, any time the knock sensor hears detonation or ping the ‘knock count’ jumps. The PCM sees this increase in knock count and pulls timing (knock retard). The PCM will continue to pull timing to avoid knock again. Then the PCM will gradually add back the timing until it gets back to full spark advance. If the PCM hears knock again before it recovers from the last event it starts all over again. The key is to focus on the knock count, not the retard. Evaluate when the knock count jumps. That's where the tuning needs adjusting.
I did some playing around and I noticed something...
When I open the throttle to accelerate aggressively (not WOT), I see some knock retard, but the knock count doesn’t change . I would see knock retard come on 3-4 degrees, but not see knock count increase at all. So this is like the car isn’t hearing knock, but IS pulling timing. This looks like Burst Knock to me. Which makes sense as to why when the sensors are disabled, no knock count but knock retard. Wouldn’t ‘Burst Knock’ really be ‘Knock Retard’? I think so.
BTW, I’ve noticed a burnout almost always causes a jump in the knock count. If you’re at the track, then you get timing pulled for the whole run even though it may not have any knock during the run. You might want to turn the Knock Sensors off when you go to the track..
A refresher for those that already know, any time the knock sensor hears detonation or ping the ‘knock count’ jumps. The PCM sees this increase in knock count and pulls timing (knock retard). The PCM will continue to pull timing to avoid knock again. Then the PCM will gradually add back the timing until it gets back to full spark advance. If the PCM hears knock again before it recovers from the last event it starts all over again. The key is to focus on the knock count, not the retard. Evaluate when the knock count jumps. That's where the tuning needs adjusting.
I did some playing around and I noticed something...
When I open the throttle to accelerate aggressively (not WOT), I see some knock retard, but the knock count doesn’t change . I would see knock retard come on 3-4 degrees, but not see knock count increase at all. So this is like the car isn’t hearing knock, but IS pulling timing. This looks like Burst Knock to me. Which makes sense as to why when the sensors are disabled, no knock count but knock retard. Wouldn’t ‘Burst Knock’ really be ‘Knock Retard’? I think so.
BTW, I’ve noticed a burnout almost always causes a jump in the knock count. If you’re at the track, then you get timing pulled for the whole run even though it may not have any knock during the run. You might want to turn the Knock Sensors off when you go to the track..
Last edited by Catskynr; 02-26-2004 at 04:51 PM.
