Allowing ECM to manage spark timing, thoughts

after working on the spark timing tables and getting them where I thought it was close I added 5* to the high table and removed 5* from the low table then allowed the ECM to start tuning the timing and me watching the Knock Learn factor. When it started the learn factor was 0.00 but after a couple 30 minute drives the Knock Learn Factor has worked its way to .89 to 1.00.

I'm wondering if I should set the high table to the MBT table and allow the ECM to set the timing based on the Knock Learn Factor. This would set the high table to the maximum recommended settings and then set the low table low enough to allow the ECM to adjust for bad gas or what ever it thought it needed.

Thoughts please,

I'm tuning my 1996 K1500 5.0L with 0411 ECM conversion (ECM thinks its a 2002 Chevy Van), Truck is OEM stock except for a Flow Master Muffler with dual outlets

Neal

I wouldn't do it that way, especially in an older vehicle with a PCM swap.

Factory calibrations already make it so the computer is the one controlling the timing. They already have the high and low octane tables use different values and the computer will pick and choose the timing between the two if there was knock.

What you've done is already fine, keep the high octane table a few degrees higher than the low and it will do the rest for you if there is any knock sensed.

I'm pretty sure the GEN 3 computer work backwards from what you think as well. Meaning 1.00 means there is no knock and it's using the high octane table.

5FDP, I may not have explained it correctly, I understood it to be as you explained it, 1.00 as high table biased and 0.00 as low table biased.

I should have included that I made both tables the same then tuned to the fuel I normally use (low grade).

charcole, what method do you use and what should I be concerned with doing it this way,

appreciate your input

Drive the vehicle, log it. If you're seeing knock, reduce the high octane in those areas. Letting the knock sensors do their thing is just fine, but don't rely on them to learn itself between too much and too little. The same way with tuning the fuel tables. Sure long term fuel trims can take care of fueling over time, but the purpose of tuning is to dial it in to what it wants and needs, then letting the monitoring and sensors do their thing for anomalies and abnormalities.

Thanks for the explanation charcoal, I understand your point

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Originally Posted by charcoal03silvy

I wouldn't do it that way, especially in an older vehicle with a PCM swap.

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I agree, maybe its my outdated line of thinking but i setup my tables to act like a distributor. After about 2500 RPM especially on an old SBC with vortec heads you want atleast 28 degrees of timming between 80-100kpa. If you're getting knock its a fueling problem.