Transmission might be toast.

[11bDad]

My tranny was slipping for the longest time during cold. Guess, what, after 6 month of going back and forth, a little $20 bluetooth ODB2 adapter found I have misfire at cylinder 7 and eventually it was triggering a code to let the dealer to fix it. after injector replaced, tranny no longer slips.

That is reassuring to hear. Thanks.

[newdude]

Both the first and second time, did you have 4th, 5th and 6th gears or did you only have 1 through 3?

[morrislee]

FYI, when the tranny slips, no codes were thrown on my dash or engine light.

 

It may appear you are at a lower gear, but if you put it in manual and downshift one extra gear, you will notice RPM goes even higher as it is slipping on a even lower gear now.

 

Looks like any time when the engine detects misfires long enough (maybe 10-15 seconds consecutively) it will unlock the torque converter and allow slipping to achieve higher fuel flow/RPM to compensate ignition.

 

Sometimes it comes back to locked state on the torque converter, sometimes it doesnt. temperture also is a playing factor on the misfire.

[11bDad]

I could eventually get it to shift up into the higher gears, but I had to work at it by aggressively pressing the gas pedal to gain speed & let off. It would upshift & eventually I could get into 6th. It wouldn't shift using the Manual button. Rpm's were a bit higher than they normally were, but I was able to drive the 140 miles back home on relatively flat interstate. The second time, on the way to work, I was in congested Interstate traffic, and while slowing down (approx 4th gear), it downshifted hard & the check engine light came on. I was able to get it to work, and when rush hour traffic was finished, I babied it back to the dealer. I understand how a fuel injector issue could cause problems with the tranny, and how replacing all 6 of the injectors would eliminate that issue, but I'll be surprised if the transmission hasn't been damaged through all of this. Hopefully it will be ready to pick up tomorrow, as I'm headed out Wed morning for a 5 day motorcycle trip to NC, Tn, and Va. If it's not ready tomorrow, I won't be able to pick it up until this coming Mon. If the new injectors don't fix the problem, I would hope the dealer will press GM to replace the transmission.

[HondaHawkGT]

GM transmissions are insanely sensitive to operating conditions. Even just airing down your tires by a few PSI will throw my 6L80 into a fit for nearly 1k miles as it adapts pressures/shift times/etc due to the increased rolling resistance. It's very easy to see how a loss of engine power due to misfires could do the same. It makes you wonder about just how many of guys on here complaining about shift quality issues probably have similar underlying issues.

[11bDad]

I have no reason to doubt the tech's reasoning for wanting to replace the fuel injectors, but I have never noticed any misfiring, rough idle, etc. with this engine. The problem with the injectors must be so slight, or at least not noticeable. The only thing out of the ordinary, that I'd noticed before the incident, was that normally running 70 mph the tach would be registering 1750 rpm, but I had noticed on several occasions that at 70 mph, the tach was at 2000. This was on flat interstate that I drive daily. I thought it was abit strange, and started wondering if the torque converter had started slipping. I don't know. I'm into the 3rd week of dealing with this & I'm just tired of it.

[HondaHawkGT]

You could try using the Torque Pro app that morrislee mentioned. It's a pretty cheap Android app that you use with a blutooth obdII adapter and will allow you to see what the engine and transmission are doing in real time.

[11bDad]

Dealer called me at 5:00 & said it was ready to pick up. Tech wrote " Trans won't upshift to 6th. Sticks in gear. Found P0700 Code sent from TCM: Emission related issue. Cold Start. Tested injectors at cold start. Found misfire in all injectors. Contacted TAC (Case # here) Replaced all six injectors as instructed. Verified repair". Seemed to operate normally on the short 3 mile drive home. Won't get an opportunity to really check it out until after the bike trip. Later

[everclear86]

I'm having a similar issue. On startup the engine runs smooth and normal but yesterday leaving from work I accelerated from a stop sign and heard a clunk and then the truck had a vibration to it and seemed like it had no power. The clunking happened a few times on the way in to work today as well. Coming up to a stoplight, the truck shakes pretty bad and has a growl to it. Never has done this before and I have 50k on it. I will check MAS tonight along with tire pressure. I have no idea what it is.

[11bDad]

One mile into my trek to work and, once again, it doesn't want to upshift. From 1st through 3rd it revs to 3500-4000 rpm before it shifts. Not sure about the higher gears. Didn't want to test that out on the interstate in rush hour. Waiting on the dealer to start answering their phones so I can take it back. Jeez

[O_J_Simpson]

Drive it until complete failure.

[11bDad]

Dealer called me yesterday afternoon telling me that they had done 3 test drives, and could not duplicate the issue. I picked it up, and drove less than 15 miles when the check engine lit up. Right before the light appeared, I noticed the tach at 2100 rpm vs the normal 1750 @ 70 mph. Got off the interstate, and the slipping began again. Took it home & decided to try another dealer today. Made arrangements with the dealer I purchased the truck from, which is 25 miles away, to drop it off tomorrow. Informed the Service Mgr. of all the details, and she said she had a very good tranny guy, and was sure they could get it handled. Probably should have used them first, but the other dealer was only 3 miles from my house. Fingers crossed.

[11bDad]

Dropped the truck off at the other dealer yesterday, and had a very encouraging test drive & 20 min. conversation with the tranny tech. He was very attentive, went over all the previous dealer's work orders, asked questions, and seemed very confident that they could handle the repair. He said considering what had already been done, GM would probably give him approval to disassemble to the point of failure, prepare an estimate to repair, and if it came within $600 of replacing the tranny, then they would authorize replacement. Guy has been doing this for 40 yrs, so I'm sure my issue is something he's seen before. Stay tuned.

[JRL1164]

I'm in for an update. Very interesting and unfortunately annoying. I just wanna know the out come now.

[tainoxl]

At the very least you wont get the p050d code from the injectors. That seems to be popping up left to right these days. Good luck, mine is at the dealer now having injectors replanced.