Factory ESC / knock retard parameters-- help with values.

[GN SBS]

For folks familiar with the stock ECM's programming: What values for max/attack/decay does the factory ECM use for electronic spark control / knock retard? I need to plug the following parameters into my XFI setup.

1. Max ESC retard (in degrees)
2. ESC attack rate
3. ESC decay rate

Respective values of 15 (max), 3 (attack), 0.5 (decay) seem to be common and that's what I've been using, but wanted a few extra cents. The attack rate of 3 degrees per 0.1 second of knock seems high to me given the values that I used to see in directscan with the factory ECM (KR would move in tenths at times...). Thoughts?

Thanks,
Scott

1. Max. ESC Retard (*)This is the maximum amount of timing retard allowed if the knock sensor is activated. Even if knock is still detected once this limit is reached, no more timing will be pulled out.

2. ESC Attack Rate (*) This parameter defines the number of degrees to retard the timing every .1 second when the knock sensor is activated. In other words, this parameter is used to set how fast the timing will be pulled out when knock is detected. In the above form, with the attack rate set at 5, the timing would be lowered 5 degrees every .1 second until the knock sensor deactivated, or until the maximum ESC retard limit was reached.

3. ESC Decay Rate (*) This parameter defines the number of degrees to remove the timing retard every .1 second after the knock sensor becomes inactive. In other words, after timing is pulled out due to knock detection, this parameter is used to set how fast the timing will be added back in. If the decay rate is set to 0.50 as above, the timing will come back in at .5 degree per .1 second (or 5 degrees per second) until the ESC retard has reached zero.​

 

[dennisL]

Respective values of 15 (max), 3 (attack), 0.5 (decay) seem to be common

Since you're using 0.1 sec, you'll have to convert the attack & decay values as I'll list them in their native form.

The stock values for 87 turbo are:
1- Max Retard degrees - there are two limits. When not in PE = 15 deg; in PE = 30 deg.
2- ESC Attack Rate - this 5-value table determines the retard to add for each (one) millisecond of knock vs. rpm.
RPM Rate
0400 0.18 deg
1200 0.18 deg
2000 0.20 deg
3200 0.31 deg
4800 0.31 deg
3- ESC Decay (Recovery) Rate - this 5-value table determines the percent of retard to remove per second.
RPM Rate
0400 498%
1200 47%
2000 31%
3200 31%
4800 39%

 

[GN SBS]

Since you're using 0.1 sec, you'll have to convert the attack & decay values as I'll list them in their native form.

The stock values for 87 turbo are:
1- Max Retard degrees - there are two limits. When not in PE = 15 deg; in PE = 30 deg.
2- ESC Attack Rate - this 5-value table determines the retard to add for each (one) millisecond of knock vs. rpm.
RPM Rate
0400 0.18 deg
1200 0.18 deg
2000 0.20 deg
3200 0.31 deg
4800 0.31 deg
3- ESC Decay (Recovery) Rate - this 5-value table determines the percent of retard to remove per second.
RPM Rate
0400 49%
1200 47%
2000 31%
3200 31%
4800 39%

FANTASTIC data, though ultimately it looks like it won't just be a simple conversion. If GM was pulling 0.31* per milisecond (its time interval) that would be 31* per tenth of a second using XFI's time interval, which won't exactly produce a good result as it's greater than total timing at WOT. eek:

Looks like I'm back to using the general rules of thumb for XFI. Maybe this slow time interval is why so many XFI users don't turn on the ESC feature. Still a must as a valuable source of data and insurance for me, but I am surprised about the difference in time intervals.

 

[dennisL]

Yea you're right. The 15 degrees max matches up, and most custom GN chips change the Max in PE to 15 deg as well.

Are you using the stock knock sensor or did it change with the ECM? If its different that would explain the difference in attack rate.

As for Decay Rate, the stock ECM uses percent and it looks like XFI uses degrees, right? Again, I'm not sure how to convert these.