Torque converter "hunting"

[The_Mountain]

Has anyone else experienced, or maybe even have a solution for, a torque converter lock that locks/unlocks constantly at a certain speed? I have noticed that at about 45mph, mine seems to do this every couple of seconds. At first I thought it might be the MAF causing surging, but the RPM fluctuations seem steep enough to suggest that it's the transmission instead. It only happens under very mild load or steady cruise. Going up a hill stops it, as does accelerating, and I don't feel it when coasting either. It's almost as if there is a conflict between the lower RPM boundary where the computer tells the converter to unlock, and the speed boundary that tells it to lock up for efficiency.

 

[alrock]

I think you've pretty much diagnosed it. Might be good to reset the learning in the computer by resetting the truck. You can do that by disconnecting both battery cables, touching the ends and wiping out the learned memory in the computer. That might reset the learning so it picks up (slightly) a new shift point.

Don't know if you'll change anything long-term by doing this but you may be able to confirm the symptoms.

In my underpowered, too-heavy H3, that's exactly what I experience about 75 mph on the highway

 

[Hunner]

If it's not something more serious, you could get a PCM tune and have it hold on to shift points longer and increase to a more positive shift. That sort of fixed my problem with an 06 when towing.

What size tires are you running?

 

[The_Mountain]

If it's not something more serious, you could get a PCM tune and have it hold on to shift points longer and increase to a more positive shift. That sort of fixed my problem with an 06 when towing.

What size tires are you running?

If it really is the torque converter, I think all I need is to bump up the RPM threshold or the road speed where the converter locks. This is based on my assumption that the unlock signal is based on RPM and maybe a pressure reading somewhere or the throttle position, not speed (so the converter will unlock to allow a slightly higher RPM when climbing hills on the highway), while the lock signal is based on road speed. If it doesn't lock until a higher RPM/speed, then when it does lock it won't be so close to the unlock threshold. If someone knows what the inputs are for converter lock/unlock, that would help me immensely.

I'm running stock-sized tires.


ETA: funny how overly-interlinked everything is on computer cars. I did some more digging, and came across a post on a camaro board that mentions the same symptoms I'm having, and in his case, it turned out to be misfires/"pings" that the engine computer was detecting that weren't enough to actually throw a code, but did trigger the unlock. The only difference was that his vehicle would unlock, and then stay unlocked for a mile or so before trying to lock the converter again, whereas mine appears to be locking and unlocking every few seconds. I don't necessarily think mine is misfiring, because I would guess that it wouldn't try to lock up again so quickly if it was detecting predetonation.

I'm going to be driving from the Midwest down to Orlando in about a month. I don't think I'll have any issues out on the highway, so I'll wait to dig into this after I get back.

 

[flyday58]

Mine does the same thing around 40 to 45 mph under light loads. I was assured on another forum that it's due to the converter GM uses on these models and is indeed hunting to lock up. I'm thinking, at least on my '04, that it may be due to the miles (149k) on the driveline. A friend just put a new converter in his '09 and he said his shifts are a lot firmer now and hasn't mentioned any hunting.

If I keep the '04 I will probably put a new converter in it, but really would like to trade for an '08 or '09 if I can. My wife just got an '08 and I really like the way it drives and shifts. I live back in the mountains, a mile vertical climb over a 16-mile highway, and there's a world of difference between the two trucks.

Back to the thread, at highway speeds hunting is never an issue, and like you said, under a load everything works fine. It's just loafing around town where it hunts.

 

[The_Mountain]

Thanks, flyday. Good to hear I'm (probably) not imagining things. I'm debating whether or not to start digging into the transmission. I'm sort of halfheartedly looking to sell my truck because I decided I didn't want some of the options it has, and since it runs ok at the moment, I kind of don't want to put a bunch of "nice-to-have" money into it that I could put to better use in my "forever" truck.

 

[Zach]

Just started having this issue. Take it in to work and find out for sure. I'm at 212k. Trans has been gone through twice. Original converter though

 

[flyday58]

Thanks, flyday. Good to hear I'm (probably) not imagining things. I'm debating whether or not to start digging into the transmission. I'm sort of halfheartedly looking to sell my truck because I decided I didn't want some of the options it has, and since it runs ok at the moment, I kind of don't want to put a bunch of "nice-to-have" money into it that I could put to better use in my "forever" truck.

I'm there, too. Really like the '04 but REALLY need the 6.2 and 6L80 tranny combo in the 08/09s. Guy I bought my wife's '08 from just located another '08 for me to look at, so we'll see where it goes. Alreadt put enough into the '04 if I'm not going to keep it.

 

[4speedfunk]

Typical when you run 35" tires with stock 4.56 gears. PCMofNC can tweek the chip to help this issue.

 

[Zach]

Apparently mine is more than a torque converter.

Lost third and fourth gear today. The pig is getting a gm reman trans this week