1991 190e 2.3 0% duty cycle
 

Hey guys, i really need some info here! I recently purchased a 91 190e, and am not too familiar with the engine management system. The car idled high when purchased, and after some diagnostics, found the throttle position sensor to be bad, i replaced it and now it idles well. I attempted today to check the duty cycle at the X11 port between pins 2 and 3. Engine off, the duty cycle was calculated to be 85% which according to landiss indicates a california controller. After startup and at operating temp, the duty cycle seems to be 0%, that is, pin 3 has battery voltage and does not fluctuate. I attempted to adjust the CO at the afm, but this had no affect on the duty cycle but DID affect running. I checked to see if the O2 sensor was making a signal, and it is, oscillating around .2 volts. Whats the deal? Is the computer bad? or is the EHA not responding to the computer? Can anybody turn me on to some shop manual reading on this subject? thanks!!

update. i was out tinkering and found the computer is getting voltage and the overload protection relay is functional. With the computer unplugged, the car will start, but the idle is high and fixed, but when plugged in, it idles well. With the EHA unplugged, it idles up for a moment, but is compensated for by the idle control motor. As a side note, while diagnosing, i found the alternator is producing near 15 volts at times. I figure i'd better start looking for a good used computer and a new voltage regulator! anybody have a 0% duty cycle before?

On the 1991-93 190E 2.3's, MB designed the ECU to show duty cycle ONLY when it was in the diagnostic mode. You needed a "impulse" style counter to make the ECU go into that mode.

On the California version that is built into the diagnostic connector by the battery.

Of course you can set duty cycle at the EHA by measuring current flow there

WELL!! That certainly clears things up. Thanks so much for that, i was really chasing my tail. I suppose i'll build the little LED tester and see whats going on. Thanks again for un-confusing me!