Unknown factor effecting ignition despite spark source remaining unchanged

Car is a 2018 F150 2.7L.

I have this odd issue with something adding in to the ignition output that I can't locate. Spark source remains borderline the entire run, but you'll see timing picks up these frequent 2 degree drops. They are not showing up in the logging as corrections and I've picked up every advance related parameter I can.

At first I thought it was due to the throttle closure (working on WGDC, separate issue) but even when throttle is fully open during the run the drops are there.

Another minor oddity, I did a similar log using an external OBDII tool and the standard timing advance cyl1 parameter, sample speed around 6hz, and did not see the timing drops in its trace.

Bonus points if someone can tell me where the "popcorn" torque max source comes from. :)

Attachment 87650Attachment 87651Attachment 87652

Could it be from the proactive cylinder specific 2 degree timing pull mapped in? Maybe it's being included in the logging parameter on some sort of cycle?

cylinder to cylinder offset tables:

[ECM] 38053 - Spark Cylinder to Cylinder Offset vs. RPM vs. Load: This table is used to modify the Borderline spark calculation based on cylinder offsets.

Ford bakes spark retard into the worst cylinders to proactively protect the engine

Attachment 87681

Yes but does that baked in retard on 2 cylinders reflect in the timing advance output in an inconsistent way when logging? Since my timing oscillation matches that value I suspect so. Will disable and relog later today. :)

By cylinder timing pull was the issue, the ignition advance logging parameter cycles through it probably depending on the firing order at the moment the sample is taken.

Glad you got that sorted.
Ive no access to VCM editor as tend to read forums at home not work, but with Ford Ecoboost, “Popcorn” is usually the Low Speed Pre Ignition load limiting tables. (LSPI)
there should be three of them. (Low med high Oct) and will be inload values.

Log load desired / actual and you should find the cells in question.

Perfect, thanks.

I couldnt open your map but you need to see if the knock correction is global or per cylinder (under knock settings). If it is per cylinder you need to log per cylinder ignition correction(i dont believe you are logging the correct knock parameters). The ECU will pull and add timing per cylinder if in this mode so all 6 cylinders can be running different timing.
the ecu also adds timing until it hits a timing limiter (combustion pressure limit, LSPI limit, or MBT) or a limit of how much advance it can add (under the knock tables based on load and RPM). You can look at an individual cylinder's timing and timing correction and see how they relate to each other in a log. A sharp drop in ign corr is usually knock were as a more squigly drop is usually bumping up against a timing limiter.

yea popcorn is LSPI as others have stated. The low medium and high load limits for LSPI are going to be based on your OAR (or KOM for the new cars). Depending where the KOM/OAR is its going to blend tables between low/mid/high. Borderline timing also has a modifier based on OAR/KOM.

Quote:

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Originally Posted by MLEcoboost

I couldnt open your map but you need to see if the knock correction is global or per cylinder (under knock settings). If it is per cylinder you need to log per cylinder ignition correction(i dont believe you are logging the correct knock parameters). The ECU will pull and add timing per cylinder if in this mode so all 6 cylinders can be running different timing.
the ecu also adds timing until it hits a timing limiter (combustion pressure limit, LSPI limit, or MBT) or a limit of how much advance it can add (under the knock tables based on load and RPM). You can look at an individual cylinder's timing and timing correction and see how they relate to each other in a log. A sharp drop in ign corr is usually knock were as a more squigly drop is usually bumping up against a timing limiter.

yea popcorn is LSPI as others have stated. The low medium and high load limits for LSPI are going to be based on your OAR (or KOM for the new cars). Depending where the KOM/OAR is its going to blend tables between low/mid/high. Borderline timing also has a modifier based on OAR/KOM.

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Thanks. It's per cylinder on this one.

The basic issue was the per cylinder fixed retard. When I zeroed that out then the timing parameter stabilized. I'll have to evaluate whether I want to keep the fixed retard in there or not based on more tuning but since it's tuned for E85 right now as far as I can tell I've not seen more timing pull in those 2 cylinders than others. So I'm inclined to leave the table zerod out.

But if anyone ever sees wonky timing oscillation check the per cylinder fixed retard. :)