This has to be a stupid question, but is there any such thing as spark trims in these GM ecu’s? Much like fuel trims? It would explain a problem I’ve always had.
Reason I ask, ever since owning this 91 caprice – 16136965 $62 all the way back to ‘95, it has a part throttle ping occurring just past steady state cruise. Everything I tried in the past to correct it has proven to be a short term solution that last for only one to two drive cycles. It’s as if the ecu keeps adding spark advance until the ping returns.

I’ve tried pulling timing through the distributor, 180 thermostat, colder plugs, egr valves, latest bin, and combinations of all of these. It’s been the same with the original engine, the new replacement one, new sensors, new throttle body, etc. I’ve tried all of these and they worked, but then the ping would come right back.

I finally got a Burn2 and TunerPro and jumped into the prom. (Been tuning mustang for a few years) As I can’t yet get the ALDU working yet and just using an autoxray hand held, I took a broad stroke and pulled 6 degrees from the main spark table that covered 400 – 2000 RPM and bottom of the load to 50.

It worked, but then again, on the drive home and since, it acts like I never did anything.

So, could this ecu have logic that trims the spark advance base on the knock sensor? Don’t really see anything in the definition other then attack rate and recovery.