what can cause a converter to periodically unlock while cruising

[BOTTLEDZ28]

Sounds like a misfire to me, my truck does it too. After it unlocks, it needs to see the misfire count stay under a certain threshold for a certain amount of time before it decides it will lock the TCC again. Drives me nuts. Always happens at light load cruise, moderate load it won't do it. It will also misfire at WOT in 2nd and flash the MIL, but no MIL for the light load misfire.

You must be getting some serious misfire counts if the ECM is flashing the light at you. Im not sure how fast those OBD bluetooth scanners work but I use Dash Command and while cruising, it will only pick up about 8-10 misfires on cyl 3 and thats over a 5-10 mile ride at various engine loads. I have never got a light for a misfire at all. I also am not getting any other lights.

I guess I would have to be logging data when the converter unlocks and see if its picking up misfires counts at the same time.


FWIW, I watched the tach needle this morning as the trans when through the gears and I did notice that as soon as it shifted into 4th, the tach needle fluttered a bit between 100rpm. It did that for a second and stopped. Then, a few seconds later, the converter unlocked and stayed unlock until I could slow down enough to get the trans to downshift and then go back into 4th.

 

[BOTTLEDZ28]

As for EFI Live, I wonder if I can shut off misfire detection in the tune to see if the converter starts playing nice again. If the ECM isnt detecting them then the it wont trip the TCC to unlock right? If the converter works as it should then it should be safe to assume that it is indeed a misfire that is big enough to trigger the TCC to unlock?????

 

[RDF1]

Yep.. just set P0300 to X: Not Reported
And put No MIL in P0300 enablers.

As for EFI Live, I wonder if I can shut off misfire detection in the tune to see if the converter starts playing nice again. If the ECM isnt detecting them then the it wont trip the TCC to unlock right? If the converter works as it should then it should be safe to assume that it is indeed a misfire that is big enough to trigger the TCC to unlock?????

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[Supercharged111]

I'm sure there are a shitload of misfires happening over 4000 RPM, that's where the light goes off. I'd love to know WTF it is, been doing it for a couple years and I've been through pretty much everything. There is a place to disable misfire detection below a certain RPM, just set that to 6000 and you're done if you want to ignore the misfire like I've been doing.

 

[BOTTLEDZ28]

I'm sure there are a shitload of misfires happening over 4000 RPM, that's where the light goes off. I'd love to know WTF it is, been doing it for a couple years and I've been through pretty much everything. There is a place to disable misfire detection below a certain RPM, just set that to 6000 and you're done if you want to ignore the misfire like I've been doing.

I think my truck runs fairly well considering it has 177K on it. I put a new Delphi spider in it a few years ago and only use AcDelco products for everything else. While logging with EFI Live, I do not get and codes for misfires. I will have to double check with a buddy to see if he has a log file saved. I've logged and changed so much over the last year that I don't even remember if we disabled misfire detection in the tune.

 

[retorq]

I'm sure you've already checked but a temp sensor can cause that too. If the temp drops below 160 or what ever the setting is it will unlock and relock when it hits that temp again.

 

[RDF1]

With black box or "411" pcm?
I've never had that happen with anything I've messed with, mostly LS stuff but never had that happen. As long as coolant temps get up above 160*ish it starts locking up.

I'm sure you've already checked but a temp sensor can cause that too. If the temp drops below 160 or what ever the setting is it will unlock and relock when it hits that temp again.

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[Supercharged111]

Don't log for misfire codes, log the individual cylinders for misfire counts. Last I checked with the old spider it was cylinder 2 that was the biggest offender. Never bothered logging after the marine intake swap as it felt identical to when I had a spider in there so we can cross intake off the list of possibilities. At this point it's either a cracked head or sticky lifter. Already did AC Delco plugs and wires, new Delphi knock sensor, AC Delco cap, rotor, and dist gear too. Yes CMPRET is set properly. It's enough to make me want to LS swap sometimes.

 

[BOTTLEDZ28]

I did some logging over the weekend with my cheap Dash Command app and iphone. I had the Pids running for misfires on each cylinder. Cylinders 2 and 4 are misfiring at 2K RPM. I get a coupe here and there from 8 but its nothing bad. Its just 2 and mainly 4. As soon as the engine is in 4th gear and the converter is locked AND the engine is running steady at 2K RPM, the misfires come in and the converter unlocks.

Im wondering if its a cracked head. I did new wires and plugs the other day and a cap was replaced a month ago. No change at all.

 

[RDF1]

Wonder if doing a crank relearn would help you out any?

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