goodhands

has been scaled by 105%. My pcm was originally tuned by a professional but I was disatisfied with the results and started doing it my self. I have been chasing some kr. Anyway in my qwest to run the kr down I am looking at everything. I downloaded a copy of a stock 2003 corvette file for comparison. I noticed the MAF table was different but I have a stock MAF. So should I change this back to stock and will I have to retune the car after doing this? Could this be the cause of my kr? I will first have to verify the integrity of the downloaded file but the other areas such as the timing table seem accurate. So I am ssuming for now that the file is accurate. Any thoughts on this?

jimmyblue

iTrader: (11)

To judge the realism of the MAF table, look at the mid
throttle LTFTs. If they are way negative then that
scaling may be to blame. If right about -1 - -3 then
it can be left as-is. The minor scaling should be making
mixture richer and pulling spark slightly, not causing KR.

If the MAF table is good enough then look at spark;
the tuner may have been aggressive on the spark tables
and gotten you into KR. Most folks seem to be 29 - 30
degrees at WOT and few get by with more. Look at the
actual advance plus any KR, the sum is what the PCM
is trying to make. If the sum is higher than 30 then it
may just be too optimistic. If you are getting KR and
the spark sum is lower than this then look to WOT fuel
ratio, by O2 voltage. Note that part-throttle, low MAP
spark will be much higher, you might want to sift for
only MAP>14.2 PSI (sea level ambient being 14.7 but
depending on elevation; ditch any part-throttle data).

Presuming the MAF is realistic, any low AFR problem
(O2s less than, say, 890mV) should be assigned to PE
(power enrichment) or IFR (injector flow rate). The
IFR can be used to make up for fuel pressure fade at
higher flows. The PE can be used more to fix issues
at higher MAP, lower RPM (KR at the lower RPMs belongs
to PE because fuel system is not challenged here).

You may need & tolerate less mid-RPM spark than up top.
I know my car runs only low-mid 20s in the midband and
makes the full 29.x degrees only above 6KRPM. If you have
30 degrees in at 3KRPM and some KR, the curve may be
coming in too fast, more than needed / tolerated. Then
you might want to mellow out the slope of the "mechanical"
advance until the engine is only getting what it needs.
This subject to a proper fuel curve in place.

I would say to approach this by doing some
comprehensive logging (cell, LTFT, spark, KR, O2s, RPM,
MAP as a minimum) and figure out where the trouble
spots are, work out which of the "global" things (MAF,
timing) are wrong or right, and then get surgical (IFR,
PE vs RPM). Graphing (Excel scatter) WOT run-ups
like spark vs RPM, O2s vs RPM, KR vs RPM, KR vs MAP,
etc. might give you a more intuitive / visual idea of
whether there's anything out-of-family, or just some
falling-away-from-the-line that needs to be trued up.