Malibu Torque Converter Hunting Uphill in 3rd

[ChevyGuy3100]

Heres the links to the clips I uploaded. They are really sucky, sorry they dont show much more, but they do give you some idea. Its hard to record and drive at the same time.

http://youtu.be/4tKfSyBMf1w

http://youtu.be/8cnSwTAZzbs

 

[CBR.worm]

I knew a guy in '07 who had a new Grand Prix that was doing almost that exact thing, but in top gear - even seemed to be about the same rate of lock/unlock. He dealt with it for about 20k miles, but after multiple complaints the dealer swapped the transmission and the problem went away. I think they told him it was the torque converter, but that never made any sense to me as it seemed like a control issue. I realize the GP probably had a different transmission, but the logic may be the same.

 

[ChevyGuy3100]

Thanks man. Just what I wanted to hear I guess with 245,000 miles I should be expecting it to die soon... BUT this even I borrowed a scan tool and went for a drive. Heres something very intresting. When I press down harder to get up a hill or just to speed up at or around 55 mph, the scan tool shows TCC going from locked to unlocked. But it still says its in 4th gear. When I mash down a little harder, the rpms spring up to 3,000, holds there for a second or two, then the TCC is commanded locked again in 3rd, dropping rpms to around 2500. When I make it over the hill, the TCC unlocks, upshifts to 4, and relocks quickly. So I believe the problem is the computer is not actually telling the transmission to downshift, but just only unlock the TCC. What do you guys think now?

 

[CBR.worm]

That sounds normal. If you are cruising in 4th, the TC is locked.

If you step on the gas a little bit, the TC should unlock but stay in 4th - this will give you a few hundred RPM jump.

If you step on the gas further, it will command a downshift to 3rd, which should give you a couple hundred more RPM, and depending on exact throttle position and load, it may command the TC to lock again. If a sensor that is detecting TP or Load (MAP, MAF) is on the edge of being good, it could cycle like you are seeing due to conditions changing enough due to the TC lock to prompt it to unlock again.

As you let off the gas it should unlock the TC, shift into 4th and then lock up the TC about 2 seconds later.

If this is only happening in 3rd under moderate load, I would watch the sensor outputs - especially TP at that throttle position, but it could be anything - even a mixture issue causing power to drop and the ECU to command the TC unlocked to get the RPM up and develop more power.

It could even be a vacuum leak related to engine movement.

It is true that at 240K miles, the transmission, if original, is probably on borrowed time - but that doesn't mean it is about to die.

 

[ChevyGuy3100]

I actually dont think its a TC problem anymore. If it was the TC locking and unlocking, pressing the brake pedal should force the TCC to stay disengaged, right? I said in my original post that it stopped surging if I pressed the brake. I dont know why I said that.

It doesnt happen in 3rd. Only in 4th when the TC unlocks and I press on it little harder. I was thinking this morning... What about the engine lugging? Im not sure if there is a vacuum leak or not. Ive checked all vacuum lines outside the engine. Scan tool says Short Term Fuel Trim is 0, and long term is -7. That that means its running slightly rich?

Also, why does it say the TCC slip sitting at an idle in park is between 100-150? Its only when its at full operating Temp. When its up to operating temps, but everything under the hood hasnt gotten really hot, it does not surge.