weird spark drop

[jfclubby]

Hi, Take a look at this short log i just took. I was just taking off from a standing start very steady when noticed a big drop in power for a couple of seconds, When i got home and had a look at the log, i noticed that the timing had droped to -1.5 betwen frame 576 and 596 for some reason but there was no KR on the log, PLX AFR and GM AFR were very close so could'nt be a very lean condition. Then wondered if B5911 could be the culprit but the figures in that table don't look low enough to drop the timing to -1.5.

The pcm was in open loop as i'm still doing the auto ve, And have also posted the latest copy of the tune which was in the car at the time of the log.

Any input would be good as i'm still learning and not sure what it could be.

Regards James.

[ls1vt209]

That is very strange. Your B5911 in that range where the spark drops still should not take it down that far (-6, -8) is a little lean in the same area as well according to your log. Wonder if it is a combination of the two?

Frame 543 shows -3.5 spark very strange indeed.

[Sid447]

You're transitioning,

from the Base Spark In Gear Table to the HOT and it's causing a "hiccup" because you have B5917 set at 40kph (it's better set like the Chev tunes @ 412kph so you can make better use of BSIG.
Though 23 degrees is a bit high and it doesn't need to go much past .28 g/cyl

[jfclubby]

Thanks sid447, So can you tell me why it drops to a negative when there are - figures in that table.