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Please help diagnosing tranny problem on 1984 850 Turbo 850 1994

My 1994 850 Turbo has 102K miles. I have owned it since 36K and have followed all service intervals including tranny fluid changes. The tranny has always worked correctly. Last week I installed a modified ecu similar to IPDs and drove about 1K miles. The engine and tranny performed cirrectly. I then removed the modified ecu and reinstalled the stock ecu. The very next time that I drove the car the tranny was holding each gear too long and shifting much firmer! All the electronics of the tranny seem to be working correctly. In econ mode the tranny holds the gear less time and shifts less firm. The tranny will also start in 2nd gear in winter mode. I removed both the engine ecu and the tranny ecu and reinstalled them without any change. I then disconnected the battery for a few hours hoping to reset both ecus but not change also. The tranny acts like it has a very aggressive shift kit. It is very throttle sensitive and will downshift at the slightest increase in throttle. Could the failure and ecu switch be a coincidence? I don't have the modded ecu to reinstall to test. Any ideas?
Thanks,
Todd
1994 850 Turbo Wagon
1982 BMW 745i Turbo
1985 M535i









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    Please help diagnosing tranny problem on 1984 850 Turbo 850 1994

    Since you are comparing the current engine and tranny operation with the previous experience, it is all relative. AND, with the adaptability of the engine and tranny ECU as well as the resetting of the adaptations of the ECU's upon removal and installation, I must ask the following. How was the car driven previous to the ECU changes?

    Many people don't exactly rip their 850's every time they drive . . . well atleast not all of us :) As such, the engine and tranny ECU's adapt, requiring more pedal travel or acceleration of pedal travel to produce the same output, as well as tranny shift points. So if the car has been driven civilly in the last little while, and the ECU is pulled, and reinstalled, and running off the preprogrammed mappings, it will feel more powerful, and shift quicker. This is why many 850 owners reset their ECU's before racing their 850s.

    Give your car a couple hundred miles to adapt. If it doesn't return back to what it used to be like with the same kind of driving you have been doing previously, then I would have the ECU read and checked for damage/alteration of some kind. Until then, I wouldn't panic just quite yet.








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      Please help diagnosing tranny problem on 1984 850 Turbo 850 1994

      The car is primarily driven by my wife but I hammer it every time I drive it. It has had the same shifting properties with and without the modded ecu. Well, I did hammer it a bunch more with the modded ecu but the shift patterns did not change. I guess I'll keep driving it and see what happens. It is unbearable in sport mode so I'll drive it in econ.
      Thanks,
      Todd







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