Thread: No 2-3 Shift on hard Accel

I have a 2001 Grand Prix GT with 161,000 miles on it 3800 V6 (K) with a 4T65E trans. I first noticed some late 2-3 shifts when accelerating to merge onto the expressway last week. Yesterday, I kept my foot to the floor and the engine maxed out at ~4200 RPM and ~55 MPH, and the trans never made the 2-3 shift. As soon as I let up on the accelerator, the trans shifted from 2-3-4-TCC without an issue. Under regular driving conditions and normal acceleration, the trans shifts perfectly, but there is a slight feeling of power loss from the engine, but it sounds fine and runs and idles very smoothly. The DTCs were clean before the hard accel yesterday, but after, I had misfire faults and a generator fault. Does anyone have any idea what might be causing the shift problems?

Thanks. I got a Tech 2 yesterday and was able to shift the trans correctly and it was crisp and clean. The shift timing was right on. Today I got a EGR open fault, but the next check was clear. I was thinking MAFS until I got the EGR fault, then I was thinking clogged catalytic converter. If I remove it, are there any sensors I would need to bypass/modify?

Thanks guys. I got a new cat on Friday and put it in today. I did not bypass the O2 sensor, I simply replaced the entire cat asembly from the exhaust manifold back to the resonator (Maremont direct replacement - $201 at AutoZone). The new one was configured to eliminate the big "U" for the O2 sensor which has to help with flow. This car is mostly for transportation, so I wasn't looking to go high performance, just restore it to good operating condition.

The issues are all completely gone. I don't know when it last accelerated as good as it does now. On hard accel, it winds over 6000 rpm and the trans shifts perfectly, and if I let it, it spins the tires on the 1-2 shift.

Thanks again for your help.

Have pretty much the exact same symptoms as you did PJ. Suspected clogged cat. Took it to my mechanic who confirmed it. Replacing the cat for $300 (with the diag test) so we shall see what happens.

Anyone have any luck getting GM to replace the cat under the extended 10 year warranty? I read the notice and they made it sound like they would only replace under certain conditions. Just curious...

Thanks for post and the replys - I feel much better now about the new cat fixing my issues.

later

Well, new cat today and all is well. What a difference! Can't believe I didn't notice it sooner. Thanks again...