Why is my timing way advanced sometimes?

[Scrufdog]

Watching logs, I'm trying to figure out why my spark advance bounces off of the 41.8 degree limit I set, or just is much higher than it should be, fairly frequently.

Examples...

1700rpm, 37mph, 48 kpa, 11% TPS - should have about 25 SA, reports 40.4 SA

1850rpm, 37mph, 42 kpa, 10% TPS - should have about 25.5 SA, reports 41.8 SA

1925rpm, 17mph, 48 kpa, 15% TPS - should have about 26 SA, reports 40.4 SA

1625rpm, 35mph, 44 kpa, 9% TPS - should have about 24.4 SA, reports 41.8 SA

1400rpm, 43mph, 41 kpa, 5.5% TPS - should have about 23 SA, reports 38.7 SA

This is also the spot where I get up to 8 degrees retard. I've checked every Spark table I can find and cant find anything that would cause this weird spike. Anything oddball I should be looking for?

As far as other spots while driving, the timing lines right up with the table.

[Scrufdog]

Ok, so I found something odd.

Under Derivative Spark/ Fuel RPM Control Parameters

Transient RPM Idle Spark Correction Bias = 0.0 degrees
Maximum Idle Spark Correction = 14.8 degrees (pretty close to how much my SA is over)
Maximum RPM for Derivative Term = 1650 rpm

I checked a bunch of other 5.7 bins and all them have

Transient RPM Idle Spark Correction Bias = 20.0 degrees
Maximum Idle Spark Correction = 3.9 degrees
Maximum RPM for Derivative Term = 1600 rpm

.....

I'm gonna look up what these are, and see if it may have something to do with whats going on.

[Scrufdog]

So, messing with that just made it idle bad, took away a lot of the advance when I change 0 degrees to 20 degrees, so still looking for the problem.

For the moment I set Max SA to 36 degrees, since I dont need 41.8 at any point anyway, that I can think of.

Going to keep hunting for the problem.

[delcowizzid]

spark bias settings normally are there to allow negative spark to be commanded as tables cant go under 0 but it depends who made the xdf and if they allowed for the bias or not changing the bias from 0-20 should remove 20 degrees of timing at the crank.normally no one touches the bias settings its just there for the ecu to see negative numbers if required.its allways good to check commanded timing to real timing at the crank before doing any tuning to make sure everythings inline.its also not uncommon to run upto nearly 50 degrees of timing in cruise situations depending on vehicle weight

[Scrufdog]

is there a way to limit cruise advance on a 7427 $31 ?

[Hog]

Delcowizzid stated that over 40° timing advance is common, and it is true. WHy do you want to limit it?

peace
Hog