My son has a '85 740 that won't accelerate via the kick down on the transmission at highway speeds. Around town the transmission shifts smoothly upon hard acceleration the car will drop down one gear and then speed up. However at highway speeds the car doesn't drop a gear and accelerate. It slowly gains speed and will increase speed up to 75 - 80 miles per hour. The gas pedal is to the floor. There is no sputtering or rough running of the motor, and no slippage of the transmission. Fluids are all OK and no burned smell. Transmission has 140 k on it. Anyone had this symptom?
The ECU last three are 511. the AMM last three are 007. I was wondering if a ECU with a different last three from a newer '80s car would be interchangable without any problems? 541 544 554? Thanks for any help, Doug

The kick down will only function up to a certain speed, depending on the tension of the cable. Over 65 kickdown becomes questionable for my very tight cable. Try kicking down at 45 or 50 or 55 and search for methods of tightening them. They are attached near the throttle cable.

-Will
1990 740T

The 511 and the 007 are the proper part numbers. You might need a kickdown cable adjustment/replacement. Non turbos, not much accel at highway speeds. How long have you had the car?

Driving the car for just under 2 years. Replaced the transmission last month. 230k miles on the car, 140k miles on the transmission. Poor acceleration with the old transmission as well. Quite a difference between the '85 with the ZF and my '88 with the AW

Ok,,,just saw it was your son. Like 16? And expecting some get up and go? 4banger, auto and not very fast.

Poor acceleration may be, general maintenance. Plugs/wires/distributor/rotor/air leaks, etc....