I just purchased a 1991 740 Turbo Sedan with the following problem. It has been progressively getting harder to start according to the owner. The engine turns over but will not fire. You can short the coil and it will start and run until you remove the wire. It runs normal with the coil shorted.[&:]

 

It could be that the engine wiring harness is bad they are prone to go bad.The insulation falls off the wires then they touch together and short out.Look by the back of the head and find a gray plug I think it has 8 wires in it look and see if the insulation is off the wires if so tape them all up for now to see if it runs.If it does i would replace the harness when you can to be on the safe side.Good luck

 

After driving the car for three days I have noted the following:
On two failed starts from cold: played with the flywheel sensor and it started. On way to work today, stalled at stop light, I played with sensor wire again and it started. I have ordered a new sensor to install. Also noted that the transmission is downshifting from 4th or overdrive back into 3rd or drive at road speed. It seemed at first that depressing the button for manuel downshift several times would cause it to upshift back into 4th, but today it will not upshift to 4th and the dash arrow stays on. Could this be related to the same sensor?

 

No they are not related the speed sensor wears like that with age and should be replaced when you can see cracks in the insolation.Remove your ash tray and the compartment above it that will allow you to see the entire fuse box and relays.In the back on the left side there is a tall white relay.That is your overdrive relay it will need to be replaced that is also normal with age.On the out side of the relay the date it was made is stamped on it so you will know if it is original or has been replaced before.Good luck