PeachParts Mercedes-Benz Forum - View Single Post - When testing the Duty cycle, why do I get 50% when koeo

Wayfarer · #21 06-23-2010, 08:35 PM

I have the same reading Key-on Engine-off, that is, 50% exactly.

Pins 2 and 3 on the X11 connector read 6.25V KOEO, and battery voltage with the engine not running is 12.5V, giving me exactly 50%. The FSM clearly states that there are only two readings for duty cycle KOEO, 70% for CIS-E systems with fault diagnosis (my 300SE) and 100% for CIS-E systems without fault diagnosis (presumably some european models).

At idle I get voltage readings that fluctuate between 1.7 and 2.7, averaged that gives a duty cycle ratio of 85%, super lean, right?

I am chasing down a similar problem as the original poster: car usually stalls right away after starting, and runs rough for 5 seconds or so before smoothing out. Otherwise it runs great. Also, I noticed that at idle the economy gauge reads in the middle of the scale. So I might have a vacuum leak in addition to whatever is causing the 50% KOEO reading. The vacuum leak might explain the super lean idle reading of 85%.

So back to the original posters question: what exactly does a 50% duty cycle reading key-on engine-off indicate? Can I safely go out and buy a new OVP? Or is there anything else that can cause the 50% reading? (the ABS light is not coming on at all).

Thanks.