"Dynamic Cylinder Air" Question

[LSXtreme]

I was wondering that if the throttle % is constant if the "DCA" is normal to jump around by .15-.20??? because i noticed that when it jumps around, the timing jumps around by 10* causing acceleration to be jumpy while under boost. i tried making all the timing the same 18* where it did vary a few degrees in the area it was having the problem varies and seemed to help a little but not much..

[jimmyblue]

Jumping in CylAir is abnormal. In fact it should be as
constant as your MAP pretty much, until you get to
the regime where airflow is fading. And there you still
have a pretty regular behaving air pump (when things
go right).

What can you see as far as the nature of the jumping?
Random? Repetitive, on some kind of cycle?

So the question is, what else is jumping? See any similar
percentage-basis bumping-around in MAP reading? Any
flakiness in the MAF output? Any misfire action (a blown
out or erratic spark perhaps)? Spark quality is one thing
that can be very manifold- (cylinder-) pressure variable.
Too much gap and too much pressure means not enough
spark voltage available, perhaps.

With the rear mount turbos it seems to me there could
be some chance of boost control pneumatics (or
whatever) being laggy and that lag maybe letting the
pressure self-oscillate. You ought to see that in the
MAP voltage directly if so.

CylAir is the tail end of a pretty messy chain of calculation
and there has to be a more "real" precursor that should
lead to a fix.

[dc_justin]

Without looking at your tune or log, I'll wager that the problem is that this is occuring right at the limit of your VE tuning, correct? Take a look at your boost VE table and look for a shelf of some sort just beyond your peak MAP value. If it exists, smooth that down to a sane level and this timing drop should go away, as it is likely being caused by burst knock retard kicking in from the rapid increase in dyncylair.

[Russ K]

Use this config file, as it logs maf hz (needed for the maf histograms to work). Do you have any scans with a wideband? Not sure why the timing jumps around.

Russ Kemp

[LSXtreme]

Actually i put my truck back in SD mode just to tweek my VE a little more and the DCA stayed consistant and the timing was a nice flat line under boost. i'm getting real close to just getting rid of the maf all together cause its been giving me nothing but problems but i'm kinda curious whats causing the problem before i go around it.

i do think my VE has a little to do with the problem because when its cold its a little worse but that only last a few mins till it warms up and the fuel trims all level out it its not bad but noticeable.

[dimented24x7]

Odds are its an issue from the fact that there are two competing systems dictating the fueling. the VE may be maxing out due to the boost but the MAF still reporting airflow as its independant of the MAP.

Deleting the MAF is certainly an option so long as you have some way of fueling in SD under boost (IOW, the PCM can see MAP over 100 kPA). They both give the same end result, the mass of air in the cylinder.

[LSXtreme]

Russ K! THANKS A LOT!!! Now that i can log HZ i think that will solve this whole problem.. in my tune i just multiplied my maf table by 10% and it helped bring my trims down but but i didnt need that much in some areas and now that i can see exactly where the maf needs fuel i wont need to keep screwing with the ve table. so thanks again let me log a good hour of drive time and i'll get back with you guys.