Re: VE stability

["nacelp" <nacelp@bright.net>]

> I've been collecting tuning data through the ALDL now for 3 1/2
> months and correcting my VE table with BLM and O2 data ('730 5L sbc,
> sc, cam, headers, axxc bin).
> using data only during close loop mode and testing to ensure a
> more-or-less steady state with rpm and map corresponding to the
> correct blm cell (aldl frame are not a snapshot of a given instant of
> time), I do a long term average (i.e., more than 10-20 hours of engine
> run time) to correct the VE table (letting transient errors average
> out over time). There's a little more in terms of weighting and
> smoothing, but that's the jest of it. As a result, IMHO the car runs
> better (drive-ability) and BLM cell counts are always less then +/-6
overall
> and under +/-3 for some conditions. Now the real question....
> I looks to me as if something is varying with operating conditions to
> prevent me from narrowing this last 4% of error (it's not that much,
> but it has my curiosity). The two conditions I see this best are 1-2 hours
of
> around-town driving versus 4 hour of highway mixed with 1-2 hours
> of around-town. It looks to me like something in the system is changing
> characteristics after a couple of hours of drive time.
> Has anyone else seen this?

Yes, with most every ecm I've tinkered with.
I just have for the time being written it off as Baro inaccuracies.  I'm
curious how the Haltech is going to be with a full time baro in this
respect.

> A few of my thought of what may be going on.... appreciate comment and
> suggestions....
> -- baro measurement screwed up because of sc
> I'm collecting data on this now. The condition does seem more
> pronounce at partial throttle conditions.
> -- EGR
> EGR partial pressure correction needs updated for exhaust system
> -- inlet air temperature reading inaccuracy
> MAT sensor may be influenced by block/manifold temp

Definetly, I think Scott is onto something with his comments about that.  I
also, think his comments about the IAT corrections are very true.

> -- engine/cylinder conditions
> carbon in the cylinders changing the burn after highway driving

Shouldn't be that much of an issue.

> -- sensor temperature sensitivity
> MAP sensor may be somewhat temperature sensitive (1-2%)
> -- limitation of the tuning procedure
> maybe, but it does look like it in the data.
> -- O2 sensor
> temperature/accuracy sensitivity of the O2 sensor.

That I'll buy in a heart beat.  I think that's way the seperate the hi and
low so much when the ecm looks at it, since it is so inaccurate.

I'm at some time going to try using two maps, one just exposed to Intake
air, and the output of that one to the input of a second one that is refered
to vac..
Grumpy



----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo@lists.diy-efi.org