Question : Early shifting? Transmission changing its mind?

[96buickregal]

Hey all, if any of you remember I posted a while back about replacing my
1996 Buick Regal's 4t60-E transmission.

Well, we did, its been running great (aside from a LIM Gasket replacement )

However, a few months back I started having a problem with the buick shifting too EARLY. The shifting in this car is still very smooth so I doubt it would be a mechanical issue...

If I am driving at around 50mph-60mph, it will shift up..down...up.. down, because it will shift UP at around 1800-2100 rpm, and then it will be like 1400 rpm in the next gear, so if I want to accelerate I have to give it enough gas to downshift and to keep it in that lower gear. This car runs great otherwise.. and the transmission we got had 120k on it when we put it in.

We were thinking maybe the Vacuum Modulator is bad? Its hard to say, we've tried pulling the battery for a good minute to see if it was an electrical problem, that didn't solve it. It has also stalled on me before because it won't go from 2nd to 1st gear, but it does that once every blue moon.

To give you an idea, it feels like its always riding a gear higher than it should be.

More info:
Shifts regularly at 2800-3100 when it is running right (The problem is not consistent!)
It will feel like it is bouncing or on a rough road when it is having the shifting problem (too high of a gear, will cause the front end to shake annoyingly, like a flat tire)
It is getting terrible gas mileage it seems like, while having this problem
it might be in my head... it still bothers me

[IsaacHayes]

Check the TPS too, Or the trans itself could be having issues.

[96buickregal]

How do you check the TPS?
I don't think so on the internal tranny problems, I mean, its never had a hard shift or slippage in its life.

[IsaacHayes]

use a scanner that can read sensor output, or use a multimeter and probe it and read the voltage as you open the throttle all the way, see if it's smooth or if there are dead spots in it. Do it with the car off, but key on the on position.

It could be inside the trans esp if it wont shift from 2nd to 1st, it may be a bad shift soleniod.

The TPS sensor tells the car where the throttle is, so if there is a dead spot, it may read 0% throttle when you really have your foot on the gas then instantly read 15% and that would cause the trans to upshift/downshift. Also possibly bad shift soleniod going out could do that too.

And having the RPM's really low at 50mph is normal, especially in my car which is geared with 2.93 FDR. Yours I believe is a little better, at 3.29 I think. The biggest help there I found was replacing my O2 sensor. That got the fuel ratio better and it had more power and wouldn't have to gas it to keep up speed. I know it's annoying cause it would be really low RPM with 4th and the TC locked up, so low that the motor could not keep pulling at that speed so you give it gas and it downshifts, then you are speeding because the gears are so far apart. So you let off, it upshifts, and repeats the process.

Having a new O2 sensor helped with that, the engine didn't bog and I can actually pull in 4th gear with the TC locked up at 50mph and keep pulling without ever having the TC unlock with just a tiny bit of open throttle. It also helped keep the TC locked when pulling big hills at 70mph. Before it would never accelerate at 50mph in 4th locked up.

I'm not sure if you are describing a problem with the trans shifting too early all of a sudden, or just complaining about the shift logic of it and the high gears, which is understandable. Try the O2 sensor and check the TPS and we can go from there. I recommend a Denso O2 sensor, or AC Delco. Stay away from bosch.

[96buickregal]

Ok I'll look into the O2 sensor, its possible that its bad even if its not causing the shifting problem as I'm getting TERRIBLE gas mileage and it bogs at takeoff/low speeds even on new plugs and wires

[IsaacHayes]

Yup that's exactly what mine did when it was bad/worn out. Try and race from a take off, and it would bog then start pulling. And yeah I would go through 1/3 of a tank going 60miles on the highway.

[96buickregal]

Yup that's exactly what mine did when it was bad/worn out. Try and race from a take off, and it would bog then start pulling. And yeah I would go through 1/3 of a tank going 60miles on the highway.

Yes!! all of the above! Would a Carquest carry the o2 sensor?

[IsaacHayes]

I got mine from sparkplugs.com , a denso unit which is good, Don't get bosch, those are known to be crappy some have experienced. Denso or Ac Delco.

I got my denso for about 47 shipped from sparkplugs.com

[96buickregal]

Oh this reminds me.. My CamShaft Position sensor is bad according to the ECU code. Should this be replaced? I think that might actually explain my bad performance, hah.

[IsaacHayes]

Cam sensor is just for SFI, it goes to MPFI above 2k RPM or when the sensor is bad. It's just for idle smoothness, but might as well check it out.

[pushrod]

Hey all, if any of you remember I posted a while back about replacing my
1996 Buick Regal's 4t60-E transmission.

Well, we did, its been running great (aside from a LIM Gasket replacement )

However, a few months back I started having a problem with the buick shifting too EARLY. The shifting in this car is still very smooth so I doubt it would be a mechanical issue...

If I am driving at around 50mph-60mph, it will shift up..down...up.. down, because it will shift UP at around 1800-2100 rpm, and then it will be like 1400 rpm in the next gear, so if I want to accelerate I have to give it enough gas to downshift and to keep it in that lower gear. This car runs great otherwise.. and the transmission we got had 120k on it when we put it in.

We were thinking maybe the Vacuum Modulator is bad? Its hard to say, we've tried pulling the battery for a good minute to see if it was an electrical problem, that didn't solve it. It has also stalled on me before because it won't go from 2nd to 1st gear, but it does that once every blue moon.

To give you an idea, it feels like its always riding a gear higher than it should be.

More info:
Shifts regularly at 2800-3100 when it is running right (The problem is not consistent!)
It will feel like it is bouncing or on a rough road when it is having the shifting problem (too high of a gear, will cause the front end to shake annoyingly, like a flat tire)
It is getting terrible gas mileage it seems like, while having this problem
it might be in my head... it still bothers me

have you thought of maybe theres a adjustable vacum modulator on the trans! check it out, same thing happened to me.

[IsaacHayes]

The modulator on the trans won't change the timing of the shifts. Just how firm.

I have mine turned up 4 turns, and it shifts nice and crisp!

[pushrod]

early shifting

dear issachayes: i understand your problem a bit better after more info. modulators can change a shift point, because your restricting the vacum flow and the length of the shift can be extended, but that doesnt sound true with your problem. id be lookin at an intermitened short, you said you dissconnected the battery that wont bring up a intermitened short, the part of going down a bumpy road got me thinkin, and it all maybe related to the tourque converter, ie: bad gas mileage, shes lockin and unlocking, in and out, up and down. you would have to find the pins on your ECM that supply the voltage to the converter and go for a bumpy ride. just a thought, pushrod

[IsaacHayes]

I don't have a problem, 96buickregal does. I see your reasoning with the modulator, but he is having it shift too soon, not too late from dragged out slipping/long shift.

Yeah it could be the TC going out, I thought of that as well too, but hopefully not.

[pushrod]

trans

yep, the tc going south would be a royal pain, lets hope it turns out to be simple, pushrod