I logged the event last night with a lot of the torque data. I'm using LiveLink and my X4 to log. First thing I wanted to check was that my engine flywheel torque wasn't over my driver demand at release of the button. It is not, its worth mentioning that when the button is released you will get a torque spike as the engine hits converter stall speed.
First thing that happens is the Transmission RPM limit drops to 3235.82 RPM, Then .020 sec later Torque source 4 pops up. I'm also logging Torque Based RPM Limit, this also goes to 1 as torque source moves to 4. The throttle angle desired moves to 2 when the TQ Source 4 occurs. when throttle angle desired goes back to 85, you get some spark/fuel source changes, which I'm guessing is a result of the ecu recovering from the torque error.
Being that the Transmission RPM limit changes to 3235, I'm thinking this is where our problem lays. Why is it doing this? I've glanced through stuff looking for a limiter with that value, didn't find one. What I did just stumble across is low/reverse max VSS. This is set to 2.5mph. looking at the log again the speed sensor resolution at the lower mph seems to be poor. In this particular log the MPH goes from 2.42 to 5.34 instantly (crossing that 2.5mph threshold) as this happens the trans rpm limit changes at the same time. My current thoughts are that the 3235 rpm number is what ecu calculates the trans rpm needs to be at 2.5 mph based on the gearing/tire info I have applied. This raises the question, why does the ecu think the low/reverse clutch still needs to be applied? Thought I came up with is that we are applying this "externally" on the trans brake and for some reason the ecu still sees that clutch is applied for a brief amount of time after the button is released. Or maybe the engine rpm is above what the ecu calculates it should be at 2.5mph (possibly do to a higher stall converter) and it applies the limit?
On another thought, if I make 5 passes back to back. The VSS reads different every time, some times going from 0 to 15 with nothing in between, sometimes its smooth. If this low/reverse VSS max is what is causing our issue, the VSS inconsistency may explain why we can make several passes without issue. Good news is this should be easy to test. I'm hoping that if I lower this value I can get the problem to repeat. Hopefully raising this limit will cure our issues..
Sorry if I appear to be rambling through this as I was working out my thoughts and ideas as I was typing. I'll play with this a little on the street/parking lot tonight as long as I am able, and I'll report back. I'd like to know your thoughts on this!
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