On my 89 W126 KE-Jetronic, the duty cycle is supposed to be about 50% when warm. And I use a multimeter which has a duty cycle setting. I then need to reverse the leads as my multimeters reads % ON for Duty Cycle - Mercedes uses % OFF.

With that said, once I get an accurate duty cycle reading, the engine computer will be "stuck" at a certain duty cycle reading if there is a malfunction. This is similar to the duty cycle percentages in the following document. I don't know if this applies to your specific car? Here is that document... (See page 16.)

http://www.berlinasportivo.com/Technical/lancia/Thema832/Testing%20the%20KE%20Injection%20System.pdf

P.S. I just searched google for any old document which had the % readouts. I don't know which specific vehicle that document applies to, but may want to find a similar document in the factory service manual for your specific vehicle.