Irregular Overdrive - 1994 Olds 'Vert w/ 3.4

[ILoveSun]

I picked it up from Knoxville Sunday night. While driving through the mountains it would shudder at times trying to go in and out of overdrive. Sometimes it would engage into overdrive, sometimes it would not.

 

It was serviced about five days before I bought it including fluid and filter change. The mechanic reported a lot of sludge but no metallic shavings at all. Now that I have it at home when I am cruising on the interstate sometimes it will stay in third gear and other times it will drop down into overdrive.

 

There is no slipping in any of the first three gears and when in overdrive it still pulls up hills nicely and downshifts and then goes back into overdrive. When overdrive is not engaged you can pull it down into third gear and the RPMs do not change at all.

 

You just never know when overdrive is going to kick in or not - it's either there or it isn't.

 

Any ideas at all?

 

Thanks,

 

Greg

[ManicMechanic]

Are you sure it's not going in to OD rather than the torque converter clutch not engaging?

[ILoveSun]

Is overdrive actually a fourth gear? If so, then it's the overdrive because I can downshift into third, and there is absolutely NO change in RPM.

 

When it does actually work, at 70 mph the RPMs drop from a little over 3k to around 2300 RPM.

 

Greg

[Galaxie500XL]

I can think of a couple of simple things, and one not so simple one..

 

Misaligned shift switch...sits on top of the trans, and tells the ECM what gear you're in...usually easy to tell, because the car won't start when in neutral.

 

Bad throttle position sensor--ECM is confused about what the load is..a scantool is your friend to find this one.

 

The last one, I had experience with in my '95...I did a good bit of research, and there's a writeup I did on the forum on this..the TCC apply solenoid is sticking in the bore, leading to insufficient fluid pressure to lock the torque converter. Usually only a problem once things warm up--mine started once the transmission temp rose above 165 degrees. The ECM detects excessive slip from the TCC, and commands the trans to shift to 3rd, to save the transmission, and disables the TCC. Again, a scantool is your friend there...if this is happening, a P0741 will be set in the ECM, it will NOT illuminate the Service Engine light.

 

Unfortunately, if this is the case, the only way to fix it is a transmission rebuild...in fact, the shop had to rebuild TWICE before eliminating the issue in my 4T60E.

 

However, I did drive the car a very long time with this before rebuilding the transmission, and other than fuel mileage suffering a bit in highway driving, it didn't seem to cause any issues otherwise.

[ILoveSun]

I can think of a couple of simple things, and one not so simple one..

 

Misaligned shift switch...sits on top of the trans, and tells the ECM what gear you're in...usually easy to tell, because the car won't start when in neutral.

 

Bad throttle position sensor--ECM is confused about what the load is..a scantool is your friend to find this one.

 

The last one, I had experience with in my '95...I did a good bit of research, and there's a writeup I did on the forum on this..the TCC apply solenoid is sticking in the bore, leading to insufficient fluid pressure to lock the torque converter. Usually only a problem once things warm up--mine started once the transmission temp rose above 165 degrees. The ECM detects excessive slip from the TCC, and commands the trans to shift to 3rd, to save the transmission, and disables the TCC. Again, a scantool is your friend there...if this is happening, a P0741 will be set in the ECM, it will NOT illuminate the Service Engine light.

 

Unfortunately, if this is the case, the only way to fix it is a transmission rebuild...in fact, the shop had to rebuild TWICE before eliminating the issue in my 4T60E.

 

However, I did drive the car a very long time with this before rebuilding the transmission, and other than fuel mileage suffering a bit in highway driving, it didn't seem to cause any issues otherwise.

 

My issue is a little different because when I first drive it, no verdrive. The longer I drive it, the better chance of it engaging.

 

Something new started today. When I take off, it starts moving, and then drops down into 1st, then shifts normally. I've been driving a little more aggressively lately. Do these transmissions "adapt" to your driving style?

 

Greg

[Galaxie500XL]

Interesting...my best suggestion? Knowledge is power...I'd recommend a scantool..it doesn't have to be expensive. I paid $50.00 for my Actron CP-9110 on eBay...

 

Second purchase would be the factory service manual. I think I paid less than $40.00 for mine, and it's been invaluable in solving some hard to diagnose problems, like the recent "cam sensor fault" code, that actually was a bad CRANK sensor.

 

BTW, just one problem could possibly more than cover the cost...in the example I mentioned, camshaft position sensors are around $155.00, crank sensor was $35.00.

Edited July 26, 2013 by Galaxie500XL

[Galaxie500XL]

http://www.w-body.com/showthread.php/42020-95-DOHC-Cutlass-P0740-no-overdrive-no-TCC-when-hot

 

 

Found my old thread...one correction, though, the code was P740...

 

Best of luck resolving the problem!