Had another thread on here trying to nail down a strange TCC lock/unlock situation I was having, but I didn't get back to it for a while. Have since had some time to re-investigate the situation.
Truck is a 2005 Tahoe, P59 ecm, LQ4 6.0 swapped in. Stock engine with a baby Summit Stage 1 cam (SUM-8718R1). OE LS2 corvette injectors. MBRP 3" catback exhaust. Everything else on the truck is stock including airbox, intake and exhaust manifolds and cats.
Running fresh NGK TR6 gapped at .35-.40 and Taylor 10.4mm wires. Stock square coils.
I was having an issue where the TCC would lock and unlock (coast to locked and vise versa) when in a coast situation. PCM was commanding this and you'd feel the shudder of it doing so. Since I initially started, I have:
- completely disabled misfire detection (maxed out all tables)
- set MIN TCC PWN delay to 90
- High and Low TPS High-Speed under TPS Min release to 0%
Seems like the TCC is now staying locked and acting much better. However I'll still feel some shudder/bobble when in a coast situation. Also, while watching my tach, I'll see some flutter in the RPM. I am wondering if this whole thing is something with idle? In my previous thread, someone mentioned something looked off with potentially the airflow mode and the timing was jumping indicating something is switching between tables? Every so often, I'll come to a stop and the RPMs will drop to maybe 500 then pick back up. Maybe this is also related?
Thanks for this. I wrote it today and drove around for the day. I am still feeling this. But, I did see something interesting. Now that the TC is locking later, when I am descending down a slight grade, or even flat... going maybe 41 mph, I watched the tach bounce between 1100RPM and 1350-1400RPM just fluttering. Can also hear it in the engine.
Think I finally figured it out. Idle spark advance in-gear.
PCM was commanding coast when descending down a grade. Since TPS is low during a coast situation, the PCM then referenced the idle spark advance in-gear table which for about 0.20 airmass was calling for 16 degrees of timing. Where as in my high or low octane tables, this would be calling for 22+ degrees of timing. So in a situation where it either is (A) calling for coast, or (B) coasting, then locking up, then coasting, it would be switching between 16 degrees through 22+ causing a surge. Which of course then if it was surging it would then go back to locked and it would repeat.
Ended up coping the high octane table and placig it for idle spark advance. Drives superb now.
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