My 1990 auto efi magna seems to be selecting power mode of it own accord (?), changing down sooner, holding gears longer before changing. Does this on speeds over 60 klm, 99% of times. Have to turn engine off then the auto goes back to normal operation. Economy/power switch not operational, seems to be no economy drive (just rev's freely, O/D gone). Fluids correct and changed.
Anybody got any ideas, bought second hand like this

Easy repair steps.
(1) Remove gearbox.
(2) Take to trans specialist.
(3) Wait one week.
(4) Collect box and pay money.
(5) Reinstall.

Guaranteed fix, been there done that.

Gee I don't know why I didn't think of that.

You probably did, but were hoping that someone could provide a no-cost, no-time, no-effort type of solution.

Without sounding cynical, obnoxious or pompous (which is difficult for me lol) the symptoms you describe indicate a teardown and inspection is in order.

You could try and see if all electrical connections to the box are clean and tight, and that any solenoids accessible from the outside are operating correctly. Check TCU connections too.

For starters this does not belong in Tech Torque

Secondly, MagnaBuff did a detailed thread a while back on fixing the OD set up on these so that should be about somewhere

What you are describing maybe a fault with the tcu if it resets but doesnt hold the shift pattern

you have to fix the overdrive

a guess....... maybe try replacing the TCU ...from a wrecker
.make sure it comes out of a "TP EFI model"

it is located on the floor pan below the radio

manual says
o/d off with power on .... o/d on with economy on

The trany needs throwing apparently the previous owner cooked the motor and with that I would think the auto, I wassssss really hoping it was a sensor problem
Hoppy

Sorry to hear. I hope you got the car cheap. I owned a TP at one stage and loved the car - but it was a manual.

Maybe cut your losses and look for a 2nd or 3rd gen? Unless your TP is in pristine condition body wise, and you want to keep it for another 10 years, it is not worth the money to do up the engine/gearbox unless you can find a good engine/gearbox second hand cheap. Manual 2nd/3rd gen Magnas are hard to find, but worth tracking down.

The difference between economy and power modes is noticeable but it shouldn't be a big deal. For instance if I lost economy mode in mine, I would quite happily keep driving it permanently in power mode. I would just use a bit less throttle and hardly notice the difference. You seem to be saying that yours is barely driveable. Does the overdrive work in power mode but not in economy mode or does it not work at all?

As others have said, it sound like the TCU (transmission control unit) is faulty if it won't stay in the mode you select. I thought you said in a previous post that you've already replaced the TCU. Is that correct or was that the ECU?