Strange Problem - Calling all experts

[jamesbond2509]

I have a strange problem with my transmission. During highway cruise when the throttle is released and the vehicle is decelerating at 60-75 mph the torque converter clutch engages and disengages very quickly until the vehicle is below 60mph. This would occur 3-4 times in succession until the vehicle is below that speed. This occurs with the stock transmission tune, I have a 4l80 and 2900stall converter. Attached is a plot of the timing when this occurs - also strange. Please help!

[jamesbond2509]

TTT anybody? Joecar, Blacky

[dfe1]

The graph you posted doesn't show any evidence of the converter locking and unlocking. There should be some change in RPM as a minimum, each time the converter locks or unlocks. The only thing strange on the graph is the timing spiking up and down. When did the problem start?

[joecar]

I saw this earlier but I have been running in 4 directions... :bash:

As dfe1 said, graph doesn't show RPM change...

Log TCCMODE to see when PCM commands TCC apply.
Also log GEAR, TRQENG, LASTSHIFT, DYNAIR.

Are you sure it was the TCC relaeasing/applying in succession...?

Your timing is fluctuating wildly which will be felt as a series of surges.

[SSpdDmon]

1st - LTFT's are a bit high...but that's a different topic.

2nd - When does the PCM command the converter to lock and unlock in 4th with 0% throttle?

3rd - It looks like spark is dipping down because of the normal down-spike in timing GM puts in the high/low octane tables at idle.

My guess is...what your feeling is normal if you're running an aftermarket converter with a higher stall than stock. They tend to have a 'looser' feel compared to the 'tighter' stock converter, which acts more like a manual car when you let off the gas while it's unlocked (won't drop revs as easy). It might just be normal. I know mine does the slow fluctuation thing when the converter is unlocked and I let off the gas at highway speeds.

I'd go with what Joe said and log the above PIDs. You almost have to think like a doctor when tuning. Run tests to eliminate your way to your illness. Guessing is for witch doctors and won't get you very far.

[jamesbond2509]

You're right! I dug up some old logs and it appears when the throttle is released and the torque converter clutch Duty Cycle goes to zero, the timing swings wildly. I will log some more tomorrow, this usually happens at 60 to 70 mph when I release the throttle. If I keep my foot on very light throttle, this goes away. Any more thoughts?

[jamesbond2509]

Better pictures attached

[SSpdDmon]

Log GM.DYNCYLAIR_DMA, SPARK, and RPM to see which cells it jumps between. Then, adjust those cells in the high/low spark tables to get rid of the variations. For example, with my friends' cam'd cars, I set .20 grams/cyl and less to 42 degrees timing from 1200 to 2000 rpm to get rid of their surging since that's what the cam liked. Once you know where the problem lies in the table, then you can fix it. :)

[dfe1]

I don't know if this is relevant to your situation, (if you haven't messed with DFCO settings, it probably isn't) but I've seen similar situations when DFCO is active. Vehicle speed seems to be the actual "on/off" switch for DFCO and if vehicle speed is above the enable speed, some vehicles will cycle in and out of DFCO, even if MAP and TPS values are at the point that DFCO is theoretically disabled.