TCC Lockup While Coasting

[RonC]

I suspect that there are a number of TCC tables/parameters that are floating around in the PCM unbeknownst to us... This one, minimum ECT threshold for lockup, etc...

Yes, it looks like it. That is the other one that I would like to be able to change. These are the main two that I want to work with but can't in tuning the trans.

[N0DIH]

On the LT1 (circa 1994-1995) it is simply a switch setting.

TCC RELEASE ON LOW TPS (on/off)
TCC RELEASE WITH RAPID TPS DECREASE (on/off)
DOWNSHIFT TURNS TCC OFF (on/off)

By default the LT1 PCM unlocks TCC on decel. You might be fighting this setting if it exists on the newer VCM/PCM's.

[oztracktuning]

Im interested in a solution for this also. It would help; keep the car in DFCO better when it has a aftermarket converter. Once the TCC unlocks the DFCO turns off as well.

[joecar]

Yes, it would be nice to have those parameters... and the other trans parameters.

[N0DIH]

That is interestesting, TCC unlocking turns off DFCO? It should not, TCC ~should~ be unlocked on decel.

The key I found is pushing the rpm down as low as you can, and watch the MAP pressure (again, frame of ref is 94 LT1). I could very closely predict the DFCO turn back on point when looking at the datalogs while driving. I don't know if I ever got it below 44 mph, as at that point I am very close to 700 rpm or so.

But there was a surge there that was a pain that I couldn't get out. My goal is being smooth and seamless despite the gains.

I honestly never saw any significant gains with agressive DFCO vs stock DFCO. So I pretty much went stock GM settings with a shorter timer.

Im interested in a solution for this also. It would help; keep the car in DFCO better when it has a aftermarket converter. Once the TCC unlocks the DFCO turns off as well.

[oztracktuning]

TCC has to be unlocked for DFCO otherwise the MAP will rise quickly to idle map and there would be no engine braking effect at all.

[11sprocket]

Surely it's the other way about. If the TCC stayed engaged, it would pull the revs up and drop the MAP.
What I find is that the TCC disengages on closed throttle and the revs drop lower than the 'synchronised' speed meaning they hit 800rpm at just over 40mph. Also, DFCO seems to deactivate at 800rpm even when B3318 is set much lower. (One for the DFCO thread...)

[N0DIH]

I can say that when DFCO is active, MAP really pulls low. Now how low is dangerous to the engine? Moisture will boil at a lower temp, oil can much easier get sucked past the rings. IIRC, Jesse mentioned that DFCO has caused engine damage on race engines on the dyno after a WOT blast going fuel and broken piston ring lands. (Jesse can you elaborate the issues?). I think he said when you tear down the engine you will see a lot of piston damage.

So I am trying to figure out what other issues might be present. It seems that if you cut off fuel and still have enough air past IAC (throttle cracker?? Not sure, my LT1 doesn't have) would keep the MAP from going so low. I see on the order 10-15 kPa MAP at full DFCO. It is an awfully low vacuum, how hard is that on intake seals, head gaskets, rings, oil consumption, valve guides, valve seals, etc?

So aggressive DFCO may not be the best thing to push for...

I was able to push my DFCO down to around 600 rpm on the low end, much lower than that and it didn't matter, it still came back on anyway. Jesse said engine stall is a big deal to GM so they try hard to avoid it.

[oztracktuning]

Ive seen it stay locked a million times. DFCO is fine - almost no fuel = no heat. Far better to have DFCO activated as much as possible. Its just a matter of keeping it activated whne the brakes are on better

[RonC]

I can say that when DFCO is active, MAP really pulls low. Now how low is dangerous to the engine? Moisture will boil at a lower temp, oil can much easier get sucked past the rings. IIRC, Jesse mentioned that DFCO has caused engine damage on race engines on the dyno after a WOT blast going fuel and broken piston ring lands. (Jesse can you elaborate the issues?). I think he said when you tear down the engine you will see a lot of piston damage.

So I am trying to figure out what other issues might be present. It seems that if you cut off fuel and still have enough air past IAC (throttle cracker?? Not sure, my LT1 doesn't have) would keep the MAP from going so low. I see on the order 10-15 kPa MAP at full DFCO. It is an awfully low vacuum, how hard is that on intake seals, head gaskets, rings, oil consumption, valve guides, valve seals, etc?

I don't see any engine problems with extending the DFCO operating range. With DFCO enabled, there is no practical difference in coasting with the converter locked and coasting in gear with a manual trans which we've all been doing for years.

I would just like to have the option to keep the converter locked. My problem is that it is annoying to have it unlocking and locking all the time as I drive a lot of roads with many hills and curves.