Transman, need help - 4T80-E transmission won't shift into 4th at WOT


#1

Hoping transman sees this but anyone with an answer is welcome.



I just had front and rear oil seals and the oil pan gasket changed on my 1999 Cadillac Seville STS, 4.6L V8 Northstar, 4T80-E transmission.



Everything is running fine, no codes (I can pull all the codes, not just PCM, inside the car), and the transmission fluid is at the right level.



It shifts fine and smoothly almost all the time, just like it used to. Goes into overdrive.



The problem is, when at WOT, it won’t shift at the redline…it went past 6500 RPM into the red once and I noticed it at 7000 in the red and either backed off or it shifted, but I’m not 100% sure. I’ve since tried taking it up there a bunch of times (without letting it go into the red) but it will not shift. I drop off the gas and the RPMs drop back down and then I can feel it shift into 4th or whichever gear it should be in. It ALWAYS shifts correctly all other times, this only happens when I put the pedal to the floor and keep it there. Again, no codes showing at all and no other symptoms.



I’m hoping this is an easy fix that has something to do with the trans/engine being out for the seals. The guy who did the work (knows Caddys but is a “shadetree” mechanic) said the trans is all electronically controlled and nothing he did could have caused this.



Before, it used to shift at 6500, just before the red line, every time.



Please help!


#2

bump


#3

I’m very curious. How fast is this Cadillac going at 6,500 RPM when it doesn’t shift into OD?


#4

Different speeds, depends on what gear it was in to start with. Does the speed help diagnose this problem?


#5

I wonder if something is wrong with the tachometer. A RPM reading of 6500 in third ratio would be in the neighborhood of 90 MPH or better. Also, fuel injected engines usually will drop injector fuel pulse width when the engine reachs red line. I have heard that modern engines will not drive themselves over red line (is this urban myth?). You might connect up test tachometer to see what the actual RPM is.

Also, I believe you can grab freeze frame data from the PCM viewing all sorts of sensor readings, calculated data, and commanded output. This might be a way to determine what the computer senses the engine RPM to be; what the TPS is reading; and what the PCM expects the transmission to be doing.

In any case, the ‘bump’ might bring transman618 online to give us his considered opinion.

Give us feedback on this problem.


#6

It may be the torque converter failing to lock up at WOT.

At least this will give the thread another “bump”.


#7

UPDATE

I met with the guy who did the work and he pulled out the linkage and checked a few things and everything looked good. Still no codes, I went through all the different systems on the car (ABS, etc).

And after putting it back together it still is doing the same thing.

Researcher, you make an interesting point…I noticed when trying to take it to redline again that at around 6000 or so the tach gets a bit shakey. It never did before at the point, or any other. And it doesn’t do that anywhere else on the tach. Is there anything I could check? I don’t have a test tach or a scanner that will read realtime data like that.

Thanks for everyone’s input so far, let me know if anything else needs clarification. Hoping transman or someone else can diagnose this from afar. :slight_smile:


#8

Different speeds???


#9

Sorry, didn’t read your post correctly…I think about 85/90…wasn’t paying attention to the speedometer at the time, more the RPMs. Is this questioning part of a diagnostic or will this be a scolding about the speed?


#10

Did it act this way before the work? I have doubts that it is supposed to be in overdrive at WOT. This and many other cars will probably go faster in the penultimate gear than in OD.


#11

Sorry, I’m not explaining it properly. I was just saying that it is going into overdrive when it should, as in, I’m not getting stuck in 3rd. When I go into WOT, it always does downshift properly, but then it’s just not shifting again when it hits the redline if I keep my foot to the floor on the gas pedal.

It did not do this before the work, and I like to drive it hard somewhat often, so I would have noticed…


#12

??? WOT says alot,please,go a little deeper on the symptoms ,so we can fully understand as a group,and try to help you,you are saying 2 different things .


#13

.


#14

When I say WOT, I mean putting the gas pedal to the floor and keeping it there. Wide open throttle. When I do that, it’ll downshift and accelerate quickly without any problems, but then it won’t shift again at the redline. It goes into the red. Before, I could keep the gas pedal on the floor and it would shift nicely at 6500 RPM. Now, I have to let my foot off the gas around 5500 and then the RPMs drop and it shifts.

It doesn’t do this or anything else improperly during all the other shifting and driving. Only when I put the pedal to the floor and hold it there.

No codes…I can pull the transmission codes, ABS, airbag, etc. inside the car and it’s showing none and it drives perfectly otherwise.

Does that explain it better?


#15

22yrs fixen cars,I know what WOT means (it shows up on alot of my ROs)

good luck


#16

22 yrs fixing cars and you have no idea what is causing my shifting problem?


#17

YES SIR!

I do have some good answers(just choose not tell you,due to the fact,you already know all the answers) did you fix my mispelling of fixing,THANK You! you noticed.

S/A


#18

Where did I say I have all the answers? Obviously I don’t, since I’m asking for help here. If you have some good answers, please share them. Otherwise, stop polluting this thread.


#19

Jad, Sorry it took so long to get back with you. From what you have been explaining, to me, it sounds more like a drivability issue. Even at WOT, the trans should still shift into O/D at a certain speed. If you are at WOT and are only achieving 90 MPH something is not right. See where I am coming from?? Have a drivability guy check it first to rule out an engine issue. This is what I tell most people. Dont blame the trans just yet, lets cover all areas in order to keep your vehicle and wallet intact.

transman


#20

For what it’s worth (and this is kind of apples to oranges, but hear me out), Ford AODs won’t shift up to 4th at wide open throttle. May I suggest that it’s not supposed to upshift, and when it was doing it before, it was actually the trans malfunctioning (ie wasn’t supposed to do that)?

Just a thought.