Help on how to interpret spark retard.

[dich_rixon]

2007 Trailblazer SS
E67 LS2 4l70e AWD
Long Tube Headers with High flow cats
Full exhaust
Ram air intake
unknown Camshaft
93 octane

Hello all. I have been picking away at my tune as time allows and it is really very good from what I can tell.

My question pertains to spark knock and knock retard.

Can some one take a look at my log and tune file I have included?

The log file has a few WOT pulls. one from 1st gear and the rest from 2nd or 3rd.

I am trying to figure out what timing it wants. To keep the knock down in the log, it seems like it only wants about 17 degrees of total advance at peak torque. This seems low to me. It is noticeably quicker with 20 or so, and I don't hear any audible knock from what I can tell. Is 17 degrees about what you all are seeing?


I tried looking for some sort of pattern to explain why i will have different knock retard readings on the same log, but i cant find any consistency.

One thing I am curious about is if its possible to have different spark advance tables for each gear change? The 1-2 shift is quite a big rpm spread and puts a lot of load on engine with the stock converter being so tight.

Thanks guys.

Rich
50 AMBIENT HIGHWAY CITY WOT.hpl Log
2 BAR OS BASE MAP, LARGE DATA INPUT, ADD, SMOOTHED ENTIRE REDUCED SPARK FOR KNOCK.hpt Tune file used to log
2 BAR OS FRESH PULL.hpt tune file with changes after log

[5FDP]

I don't think it helps that both timing curves are the same, you aren't allowing it to take away timing and run knock free. Because as soon as it knocks it pulls timing, then shoves that timing right back in when it's gone, then it knocks again. Having the low octane timing at 3-4 degrees less would allow it to use the knock learn factor to help pick the timing between you low and high tables.

You're way out of fuel injector too, 5,500rpm is pushing 90%, then you go way past 100% duty cycle over 6,000rpm.

I'd also zero out your GAS spark correction table that is adding in more spark than your high/low tables. Just let the high/low tables determine what spark advance it will be running, so you aren't having something else change it on you. Experiment with different commanded AFR values too. Some may like 12.0 instead of 12.5. But make sure you get your injector stuff under control.

Low to mid 20's is avg timing to me too, like 20-23 degrees.

[dich_rixon]

Thanks 5FDP. I wasnt even logging duty cycle, i got to start logging it. Thanks. I made the changes you suggested. We will see how it goes. I will post another log this week.

[5FDP]

It was in that log, unless we are seeing different things. You only need to have your injector pulse width logged and the duty cycle will appear on it's own if you have it selected in the charts.