spark advance question

I've been looking at the timing tables versus a number of logged timing results. For years there's been the question of why logged timing doesn't always match what's been programmed. EFI now gives us the ability to see where timing is being controlled. In every case where I've looked at my cars logs, there is some point under load that the timing reverts from the high octane table to the optimal timing table. I have not been able to see a definite point except that it seems to happen with increased throttle and above 2000 rpm's. I don't have enough logged information to be sure of what the trigger is.
Two questions:
Anyone know what a definite switch point might be?
Should optimal timing be set the same as the high octane timing, at least in the higher rpm/gpcyl areas?
I suspect that in some cases this situation could be a reason why knock doesn't get solved by reducing timing in high octane.

I can't believe how intuitive you are.

I don't have a clue on this one.

Here are a couple odd Timing facts I've learned with my car (2001 Z06)

I do know that, on my car, between 2000 and 3000 RPM if the Dynair exceeds the MAF values then it drops off the MAF (onto the VE table) and the timing drops to the lowest available value. Lowest value was usually the "Base Spark Park" value. I could prop it by boosting the Base Spark value. A Tip of the Hat to Ross on this!

Also if Commanded AFR exceeds 13.8 - 14.0 in lower RPM ranges, steady throttle, the PCM will pull timing and surging results. This can be circumvented by adjusting " Fuel Mixture Spark Correction" at the apprpriate EQ Ratios. Negative numbers work to drop timing values. Tip my Hat to Ross, again!! :D

All of this is open loop info though.

Have a great weekend!!

Cheers,
joel

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Originally Posted by bink

I can't believe how intuitive you are.

I don't have a clue on this one.

Here are a couple odd Timing facts I've learned with my car (2001 Z06)

I do know that, on my car, between 2000 and 3000 RPM if the Dynair exceeds the MAF values then it drops off the MAF (onto the VE table) and the timing drops to the lowest available value. Lowest value was usually the "Base Spark Park" value. I could prop it by boosting the Base Spark value. A Tip of the Hat to Ross on this!

Also if Commanded AFR exceeds 13.8 - 14.0 in lower RPM ranges, steady throttle, the PCM will pull timing and surging results. This can be circumvented by adjusting " Fuel Mixture Spark Correction" at the apprpriate EQ Ratios. Negative numbers work to drop timing values. Tip my Hat to Ross, again!! :D

All of this is open loop info though.

Have a great weekend!!

Cheers,
joel

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Interesting info. I can't wait to get my car back. This is an area that I haven't done much with.
I did get a definition over at Tech, regarding the Optimal table.

"Max Torque Timing vs. RPM vs. Cyl Air: Theoretical spark advance that delivers maximum torque. PCM torque calculation routines reference this table when estimating current engine torque output relative to theoretical maximum. We do not recommend modifying this table."

It looks like I just jumped into a coincidence. I started looking at more tables and found that the " Fuel Mixture Spark Correction" table adds 3* timing at 12.8 AFR. That's also consistant with what I logged. Likely it's the cause. I need to do more logging.

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Originally Posted by jfpilla

Interesting info. I can't wait to get my car back .

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The forged Beast :mrgreen:

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Originally Posted by jfpilla

"Max Torque Timing vs. RPM vs. Cyl Air: Theoretical spark advance that delivers maximum torque. PCM torque calculation routines reference this table when estimating current engine torque output relative to theoretical maximum. We do not recommend modifying this table."

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I guess this is referenced with large TPS deltas??

Quote:

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Originally Posted by jfpilla

It looks like I just jumped into a coincidence. I started looking at more tables and found that the " Fuel Mixture Spark Correction" table adds 3* timing at 12.8 AFR. That's also consistant with what I logged. Likely it's the cause. I need to do more logging.

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I don't think GM enabled/used this table until 2002 with Y/F bods. Mine was all zeros. I need to look at it more closely...someday.

"I don't think GM enabled/used this table until 2002 with Y/F bods. Mine was all zeros. I need to look at it more closely...someday."
That's true for the 2002 Z06 file I looked at.

I wonder what is used to determine what the AFR is at the time spark is added?
I wouldn't think it would be the 02's, more likely the calculated PE/RPM values. If so, then it would be important for the MAF, IFR and VE tables to be right in order to have a correct PE table. Not likely. Sounds like 0'ing the "Fuel Mixture Spark Correction" table might be a good idea.

Did you ever get your timin the same?

I have a similar issue on my 05 V, i tell it to give me 60 degrees but i am only gettin 46 degrees...

I have a massive cam and need the extra timing down low to give me that little bit of smoothness