HI ALL I just recently attempted to tune my 88 740 turbo. I replaced bosch plugs with NGK. Dist cap, rotor, wires gapped at .28 my car will not crank, more less run. As I crunk it the tach gauge was jumping around and I was wondering if the wires running to the dist were faulty( HALL SENSOR)? Just wondering what the problem could be?


THANKS

As you attempt to start the engine during a no start scenario (ie crank it on the starter) it is expected and normal that the tach will knudge up slightly (not jump around though). This indicates that you do have primary ignition pulses to the coil negative terminal. This in turn means your hall is sending out it's signal to the ICU and in turn the ICU is sending pulses to the ignition amp and from there to the coil negative terminal.

So your problem is likely on the high voltage side which is what you worked on.
Plug wires mixed up?
Remember to put in the new rotor? (don't laugh, I did that once)
Wire form coil to distributor installed? (forgot to connect that once too)

Have you checked to see if you have spark at the plugs?
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David Hunter

Hi there,
While you are cranking the engine , your tach should move up and down .. that means that your hall sensor is working.. Try to spray starter fluid and crank the engine up.. if it start and rev and then dies your ignition is fine and start looking for a fuel delivery problems... But i assumme ( i know assumption is bad..) when you were installing rotor or the cab you did not install it properly or should i say tight/fit. Recheck your work.. and start from there..
Another question is was the car running fine before you perform the tune up?
Have great day
And good luck
Sammy

I removed the new plugs and put the old plugs back in it ran a little better. So I'm in the process of removing the new and replacing the old to find out what the problem is. Yes, the car ran fine before the tune-up.