ZZ 502 1995 era FI from Street and Performance Mena AR (gone now). ECU 1227730. AUJP V5. Recovering drivability after changing to the ZZ502 short block with the Cam they provide

This car is a driver. It lives at 7,500 feet, but spends a significant amount of drive time at close to sea level.

I used 84ELKY's SA Table Build Sheet for preliminary SA tables (example attached). Pretty much as he had in his example. 32* at 3200. Idle 21.09*. I have PE set at Zero, using the VE table for the upper range.
Some knock Retards in the 40-50 KPA range 1200-2000 rpm.
Adjusted some values generally reducing the SA across the Board.
No Change (or insignificant change)
Reduce SA values again.
Same lack of result.
A couple more times, still KRs in that RPM/MAP range.

This issue has caused me to wonder about how thin air impacted spark advance settings.

Here's my theoretical questions.

1. I am tuning this engine at 7,500 feet above sea level. 100% MAP is about 72 KPA. The result of the Build Sheet Excel Program is the Start point of SA table is built around 100% KPA. At this altitude, with WOT actually in the 70 KPA range, the SA is advanced beyond what it would have been at sea level. Seems a no brainer to just adjust the SA table to the left essentially moving the WOT SA levels to the 70 KPA column. However:

2. Unless I am missing something, unlike VE settings with NBO2 sensors recognizing the change in air density as you drop in elevation, how does the ECU translate a drop in elevation to the SA tables. If I have WOT settings at the 70 KPA column and spread SA settings down from there, won't the engine be "retarded" across the board at sea level.

3. Does something happen (like PE or AE) that might impact the SA tables in the range noted around 45-50 KPA and mid RPM levels that I need to look for or consider. I have easily dropped 2* out over several runs and still see the Knock Retards.

Don

 

High altitude usually requires additional spark.

if map is 72 kpa at 7500 feet for atmosphere, map will move toward 99-101 at sealevel

so wot at 7500 ft will run in that 70 kpa column. Move to sealevel the engine will use what is in the 90-101 columns.

so you can retard timing a little bit if needed in those 90-100 kpa columns For wot because 70 kpa should be a few deg higher than 90-100 normally anyway.

Part throttle cruise will move up higher in kpa as you go to sealevel as well and timing is usually less as you move into higher kpa so there is some reduction there.

problem is you may need extra fuel as well. Closed loop may handle some but not all esp not all wot changes. That i dont know if there is a barometric pressure compensation method for fuel and or timing like some aftermarket ecu’s. Been a while since i looked in those files.

there can be some pe mode advance. Should be a table for it i would 0 it out and setup your main regular table.

also note some knock can be false. If you yank a lot of timing and still see it, could be false. Just keep that in mind

 

I think I need to build the table around a set of values that will work at both elevations (and in between). I set up the next table with the assumption that I was at sea level. 32* advance at 3200 rpm at 100% MAP. I found the log that had the minimum Knock retards (only four cells 1000. 1200, 1400 rpm at 50 KPA and 1400 at 40 KPA.) I finessed the table to drop the timing in those four cells. Let the rest of the chips fall for now.

I recognized something else. The smoothing function has been a contributor to the repeated problem. You have a series of values. The low end is basically fixed (Idle SA). The upper end is basically fixed (something close to 32*). Regardless of what values you manually insert between Top end and Idle in each KPA column, the smoothing function brings you back to about the same set of intermediate values.

I didn't use the smoothing function this test.