VS Transmission not locking when hot

[quadfour]

Hi Guys,

I have a 96 VS, one of the first series II. It's a V6 with the standard 4l60e you find in VSs... It's done about 215k for memory and is in alright condition.

Problem is that the automatic transmission is playing up with regards to locking of the torque converter. The symptom is that in 4th, the torque converter will lock when its cold (just started), and wont lock at all when it's hot (normal operating temp). The problem has been around for about a year... I tend not to do much with the car and so I've not worried about it until now.

I've searched the forums at length and only found one other mention of this issue, but there was no notes on how it was fixed (if it was fixed). Otherwise I found information about how the PCM/ECM decides to lock the TC... Based on speed, engine temp, throttle % etc.

I've also been using the ECM self-diag codes to find a couple of non-related issues (well I think they're not related). Here's a list of stuff I've done and tested trying to find the issue:

1) Serviced transmission on 8th Sept 09, new oil, filter etc. Couldn't see any issues with wiring harness or solenoids.
2) Tested thermister inside transmission. ~3k ohm at 15deg C, rapidly decreases with heat applied.
3) Replaced wiring harness external connector O-Ring (was leaking trans fluid before)
4) Replaced transmission dipstick (old one wouldn't seal, rubber went hard)
5) Replaced crank angle sensor (computer said it was an issue)
6) Replaced engine wiring harness (old one burned out behind alternator)
7) Tested TPS, ~2k ohm at 0%, ~10k ohm at 100% (have not tested output voltage, just resistance)
8) Reset ECM (removed battery and engine fuse for a while)

Now the EMC reports all OK (code 12), and back to the same issue. Everything else seems to work fine. Transmission shifts up and down normally and smoothly in all other cases. Oil level is perfect, and I threw in some Wynns auto-conditioner stuff (to free up any sticking valves etc).

I'm at a complete loss as to what to do now. Does anyone have any suggestions or know where else I can be looking??

[shiftySLE]

What do you mean not locking, all a lock up converter does is drop a few hundred revs to save fuel in top gear, is this what its doing?

[quadfour]

Yes, it's this locking that isn't occuring. The fuel consumption through the torque converter not locking actualy adds up to a bit if you're doing long stretches on highways like I have... Without the locking, it's pretty spongey in 4th at 110km+ making it hard to just rest my foot (no cruise control )

[HARVZ-6]

theres a heat override for lockup

my vt suffered the same issue but the trans was tired

chances are thats whats sending it off

[shiftySLE]

Lock ups do have their problems but due to fuel consumption they also have their benefits, what do you mean spongy? When you put the put down a bit it almost feels like its dropping a gear.

[shiftySLE]

theres a heat override for lockup

my vt suffered the same issue but the trans was tired

chances are thats whats sending it off

What did you have to do, new converter?

[quadfour]

theres a heat override for lockup

my vt suffered the same issue but the trans was tired

chances are thats whats sending it off

Is this heat override thing taken off the internal transmission temp? Or from something else? I've tested the transmission's internal thermistor, tested within spec (at least according to google). Or does this override happen at the ECM level? How would you have fixed yours?

[quadfour]

Lock ups do have their problems but due to fuel consumption they also have their benefits, what do you mean spongy? When you put the put down a bit it almost feels like its dropping a gear.

Without the TC locking, at 110km/hr, revs will go anywhere from about 2.2 to 2.6... going downhill, it picks up speed and revs quickly until i take my foot off. It's just because the auto is happy to slip under moderate throttle (without dropping a gear). When locked up, it's more responsive to the throttle as there's no slip.

[HARVZ-6]

i fixed it be replacing the trans haha

i knew the trans was wearing.. it held up for over 300thousand ks with a realll hard life and that was its only issue

if its over heating its most likely slipping,

a good service would fix myne for 1-2000ks but then it started again

i got a second hand trans with 100thousand ks for 200 bucks and swapped it over in a weekend no probs since

[hako]

Check this link ....it may help:
4l60e Lockup Issues And Probable Causes And Fixes Fyi - CamaroZ28.Com Message Board