Crazy RPM issue - Transmission? Misfire?

**TA76** · 09-11-2013, 04:39 PM

OK, trans was rebuilt at about 30K (this car has been babied), went back with a TCI Streetfighter converter when I did the rebuild. Had some idle issues which some guys here were nice enough to help me diagnose as simply needing the CPU tuned for the new converter. Car has run just fine until recently, it is doing something very odd. Seems to happen after about 10-15 minutes of driving. Cruising at 75mph the RPM starts to jump or really die off then come back. I'm wondering if I'm seeing another transmission problem or is this a misfire? Any advice would sure be appreciated.

http://s70.photobucket.com/user/Wyat...a982d.mp4.html

I've only noticed this at cruising speeds and have not observed it happen below 70mph (it might though). Only other odd thing as transmission seems to rev higher than usual when shifting from 1-2, especially when I give it a little extra gas. This could be my imagination though. Also, no check engine light.

**Decadence75** · 09-28-2013, 10:38 PM

Originally Posted by TA76

OK, trans was rebuilt at about 30K (this car has been babied), went back with a TCI Streetfighter converter when I did the rebuild. Had some idle issues which some guys here were nice enough to help me diagnose as simply needing the CPU tuned for the new converter. Car has run just fine until recently, it is doing something very odd. Seems to happen after about 10-15 minutes of driving. Cruising at 75mph the RPM starts to jump or really die off then come back. I'm wondering if I'm seeing another transmission problem or is this a misfire? Any advice would sure be appreciated.

http://s70.photobucket.com/user/Wyat...a982d.mp4.html

I've only noticed this at cruising speeds and have not observed it happen below 70mph (it might though). Only other odd thing as transmission seems to rev higher than usual when shifting from 1-2, especially when I give it a little extra gas. This could be my imagination though. Also, no check engine light.

That does sound very similar to what I have going on. I was beginning to think mine was a trans issue until I saw this. Unfortunately I have not found a solution yet but am still looking. I was not able to see your link though.

**tekkauto** · 09-29-2013, 05:26 PM

That tachometer surge looks just like a torque converter locking and unlocking rapidly. I would think you would have a check engine light but if your pcm is modified, it may not be monitoring this correctly and seeing this as a problem. It may very well be a failing torque-converter or a electronic solenoid issue. Ive seen this many many times before at my GM store. The reason it takes 10-15 minutes of driving to start acting up is because TCC lockup will not occur until normal engine operating temperature is aquired.

**TA76** · 10-04-2013, 08:34 PM

tekkauto, thanks and I think you are right. I've emailed the tuner and he said the misfire detection is turned off as part of my tune. The fact that the car ran fine for 6 months also caused me to think it might be mechanical rather and a tune issue. So... is the electronic solenoid something I can easily test and or change? I've had a serious run a bad luck with my cars lately!

**tekkauto** · 10-06-2013, 08:19 PM

The TCC solenoid is in the valve body and can be replaced by dropping the trans pan, unplugging some wires and does not require valve body removal. Book time on the repair is 1.4 hours (motoralldata time).

**SteveC** · 10-07-2013, 04:46 AM

Originally Posted by tekkauto

That tachometer surge looks just like a torque converter locking and unlocking rapidly. I would think you would have a check engine light but if your pcm is modified, it may not be monitoring this correctly and seeing this as a problem. It may very well be a failing torque-converter or a electronic solenoid issue. Ive seen this many many times before at my GM store. The reason it takes 10-15 minutes of driving to start acting up is because TCC lockup will not occur until normal engine operating temperature is aquired.

+1 on this, did the tuner adjust your shift points in the PCM?

SteveC

**TA76** · 10-13-2013, 04:13 PM

Yes, I'm pretty sure shift points were adjusted. I'm thinking this is a TC issue, which really sucks since the unit was new and has very few miles on it.