Spark Source at WOT - MBT/Base back to BKT?

[metroplex]

Does anyone recall what needs to be done to ensure that at WOT the spark source is using borderline instead of Base/MBT?

I figured this out on my 2014 SHO but the newer Ford ECUs seem to want to use Base/MBT instead of borderline even at part to mid throttle, but mostly at WOT.

Before you say that BKT exceed MBT and that's why the ECU is using Base/MBT... My BKT at WOT is lower than MBT, so there's no logical reason for it to use MBT at WOT. I can understand partial to mid throttle cruising where BKT is generally higher but it is still using Base/MBT in normal driving.

With the stock tune, it would use Borderline at WOT.

[engineermike]

Check all the adders and modifiers. You may know this already but you can?t just compare the Bk and mbt tables side by side. Mine always uses the lower of the 2 once you factor in all the modifiers. Also there?s something weird about when it adds knock advance. Like if it starts at borderline and adds knock advance it will stop advancing once it reaches mbt but still show borderline as the spark source (?).

[Grim5.0]

interesting have not seen that one, mine functions as mike describes. Lower of the the two and the source PID lists the base table being used regardless of adders (borderline or mbt/base).

if you plot mbt against borderline and then actual advance, are the pids correctly reporting whats in the tune? pick a few points, and double check the expected timing

[metroplex]

Yes the spark source is accurate. When it says Base MBT that is what I see as the actual advance. I also log BKT and MBT and can see the deltas. When I went back to stock cylinder pressure limit, it started using that at WOT but I can see why as that is much lower. But BKT is lower than MBT at WOT so I am unsure why it still uses Base MBT during WOT.

[LastPlace]

You have modifiers making you hit mbt for those mapped points.

[metroplex]

I'm not as worried now, but my BKT is still lower spark than MBT but it chooses MBT at WOT. When I lowered Cylinder Pressure Limit to factory stock, it started to use that (which was close to what I had for BKT).

[LastPlace]

Look Your modifiers for borderline and Mbt

[metroplex]

Look Your modifiers for borderline and Mbt

Which tables in particular?

[engineermike]

Lambda for both and charge temp for borderline. Maybe more.

[metroplex]

They are all stock

[engineermike]

Ok, but they still affect it. borderline can be modified by octane adjust, lambda, coolant temp, and charge temp. Mbt is modified by lambda. You have to apply the modifiers before you compare. Or, do like me and log mbt and borderline in vcmscanner. The logged values should have the modifiers built in.

[metroplex]

I always log MBT and BKT. They are night and day at WOT. Even modified it's like comparing 8* to 15* of timing. It always goes to MBT at WOT until Cylinder Pressure Limit is lower than MBT. Then it goes to the CPL table.

[engineermike]

I dont suppose youd want to post the log and tune?

[Thatwhite5.0]

All Borderline modifiers will retard Borderline spark timing aside from the ECT and IAT spark modifiers which add timing at cooler temps. Borderline Lambda could add maybe .25* WOT, depending how rich WOT Lambda is. MBT timing is supposed to be Max Break Torque and you're setting limiter in front of the MBT. You'll hit Cylinder Pressure Limit, preventing yourself from MBT. Keep Cyl Pres Limit more advanced than MBT.
You have figured it out for yourself, metro.

MBT should be less advance than Borderline at lower loads, giving more control of timing at lower loads, timing will follow your MBT tables. MBT and BLK cross paths around 40% load where MBT advances more than borderline. MBT advancing past Borderline gives the knock sensors the ability to add timing to Borderline. MBT timing has a part of the torque calculation and MBT will cause IPC Torque Errors. MBT Timing can also decrease IPC Torque Errors. A lot of people question their torque errors around 30 to 40% load, 2000 to 3500 RPM.

I max Cylinder Pressure Limit and Pre-ignition Limit at 63.5* on every tune. Every modifier is either maxed out or zeroed out except for ECT and IAT modifiers, I do not allow any modifiers to add timing, only subtract timing due to high temps. I use Knock Advance Limit and MBT timing as my spark limiter. The knock sensors will never advance more than Spark Advance Limit and timing will never advance passed MBT timing. Timing will always be consistent this way, so timing isn't 25* one pull and an hour later, timing modified itself to 29* on a second pull.

[metroplex]

I finally found the darn culprit. It was the octane modifier table (spark adjustment table) that gets multiplied by the octane adjust ratio. On my 2.7 EcoBoost application, OAR is almost always -1.00 whether on 93 octane or full E85. So I had increased the octane adjust table quite a bit. That was what was added to BKT so the end result is that MBT was lower and the PCM used MBT. I don't know why I didn't see this earlier. I had been looking at modifier/adder tables but failed to look at that table.

On my N/A 3.5 application, it always used BKT at WOT because OAR was almost always 0.00 on 87 octane, or maybe up to -0.5 or so with 87 octane and the adder wasn't all that great. Hence it just ran on BKT instead of MBT. But it turns out that the N/A 3.5 can run almost MBT at WOT on 87 octane and not have any knock correction.