89 deville not downshifting correctly
 

The car jerks back and forth at 45 to 55 mph. Doesnt seem like it wants to downshift out of OD. From what Ive read it sounds like the TCC solenoid? Ive heard you can disconnect it but I have no idea where its located. By the way the fluid is not burnt and the trans was either rebuilt or swapped( I dont know its my grandmothers car) about 10,000 miles ago. Any info would be appreciated.
Thanks

RE: 89 deville not downshifting correctly
 

Sounds like a TCC (Torque Converter Clutch) engagement problem. It should set a code. I think yours has the on board diagnostics, but I'm not positive. Press and hold the OFF and warmer (red) buttons at the same time untill the LED displays light up. It should then tell you the codes.

The torque converter clutch is supposed to engage at 41mph when it upshifts from 3rd into overdrive. If it doesn't engage then the rpms will remain high and you will get poor fuel economy. It sounds like the solenoid is working, because it's trying to engage, but when it can't it goes back into third and then tries again. You can avoid the jerking from it shifting back and forth by putting the shifter into 3rd gear.

I would suggest getting a FSM (factory service manual) by Helm, but also check the codes.

RE: 89 deville not downshifting correctly
 

Thanks for the response krashed. Im getting an E28 and E47. If the E28 is the vcc solenoid how difficult is it to get at?

RE: 89 deville not downshifting correctly
 

Well, you're lucky that it's not the TCC solenoid. I think the tranny has to come out for that.

P028 (E028) ......... Open 3rd or 4th Gear Shift Or Shorted 2-3 Shift Solenoid [VCC]
You just need to take out the valve body and replace the 2-3 shift solenoid.

P047 (E047) ........ IPC - PCM Data Problem
I would ignore this one for now untill you get the solenoid replaced.

RE: 89 deville not downshifting correctly
 

I have the same problem occasionally with my'95 and it turns out to be a fuse which allows the tranny to shift down from overdrive. This fuse is not in the box under the steering wheel. Its in the bank under the glovebox. You have to remove 2 or 3 screws from the plastic cover underneath the glovebox and pull it down to expose this box. I think its fuse 6 or so, but they're easy to check.