WOT, 6,000rpm, 13.5psi and 39.5* spark!!!?!?!?!?

[tunedportcj5]

ok guys, what the heck would command 39.5* of timing during a WOT run? This has only happened to me once (that I know of) but I can't risk this! Any ideas please?

See attached for log and tune... Thanks!

12419
12420
12421

[GMPX]

You need to log what the airflow g/cyl is doing at that point.
It doesn't look like you are, but when the E38 is in SD mode there is a bug in it's calculations for the virtual VE. A bug as in GM bug, it's true! Very early on a few people noticed that every now and then the ECM would read very low g/cyl and the spark timing would jump to 40 deg or so (like coast down) for split second. Turns out the ECM did a wrong calculation and the result was a low g/cyl number. This 'glitch' is automatically fixed when we recalculate the virtual VE coeffs, however, as you aren't running in SD mode then it's probably not going to be the cause.

[GMPX]

Err, sorry, you did log g/cyl and it's doing exactly what I thought, g/cyl drops way down to .44 with the resulting timing being 40.
As for the cause given you are running a MAF, I am not sure, I didn't think this problem happened with a MAF, only in SD mode.

[swingtan]

looking at the log, the 0.44gm/Cyl point occurs during the KR event. So it's probable that the massive knock event caused the airflow calculations to drop significantly. If the tune matches the log, then the timing should only have gone to 20' at that point anyway.

were there any DTC's recorded? I see that you have B8034 set to 105kPA, which is probably not the best idea. I'd set it to at least 200kPA for your setup.

[tunedportcj5]

Thanks sir(s) - B8034 is a new one to me. The DTCs should have been recorded in the log. Mainly O2 sensor (because they are unplugged at the moment) and TPS circuit performance. I believe its common to see the TPS errors when running a truck 88mm TB. It has sent me into limp mode a few times. Any ideas on P1101?

[tunedportcj5]

BTW, I am running strictly off the MAF. I need to source a newer E38 so I can run a newer OS to support the higher MAF tables. I have hit the limit a few times.