I apologize for the sarcastic responses above. The responders took the position that the original poster did not know what he was talking about, when in fact he was the only one who did know what he was talking about.

Did you ever resolve this problem?

My recently purchased 300E runs excellent with one exception. It sometimes stalls right after starting or stumbles for few seconds until idle stabilizes.

I checked the duty cycle from X11 connector and here are the results:

Ignition On, Engine Off: 50%
Engine at Idle: 48%-54%
Engine at 2,500RPM: 68%-72%

What would cause it to be 50% and not 70% with engine not running?

Have you replaced your OVP?

I have not and actually, ABS light came on few times while I was testing the duty cycle.

Sounds like the classic OVP failure symptoms.

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.

Me too ...
 

This concerns duty cycle measurement/adjustment on Bosch KE Jetronic (CIS) systems on M103, M104 and other MB engines.

Mine used to read 70% (or 75, whichever is right) and now it reads 50% ignition on/engine off. It hovers nicely around 52 % now and the car is running well.

Did anyone find an answer as to why some are getting 50% engine off? Or did they all get tense and pre-menstrual about posting style and then boycott the thread?

I'm sure many would like to know if any of the seriously brainy boys would help.

By the way, mine was not OVP related.

Thank you in advance.

RayH

Ray, I'm not one of the seriously brainy boys you're looking for, but I've had similar duty cycle test results, with a 90% engine running measurement. Super lean, right? Yet the fuel consumption/mileage has declined to the mid-teens city/21 hwy. At some point, I'd think we should be taking the next step and testing the O2 sensor and EHA. Maybe the seriously brainy crowd can weigh in on that, too.

I'm attacking this issue across a few cars.

190E 3.0 reports 70% Key On Engine OFF
420SEL reports 30% Key On Engine OFF
560SEL reports 80% Key ON Engine OFF

190E then throws a 50% code once its been start and has been running for a while.
420SEL runs normally, a little rich but operations are normal.
560SEL has a high idle problem, and continues to throw 80% fault.

I was talking with a gentlemen over on BenzWorld and he thinks that if the system throws a fault number with Key On Engine off that the device associated with that fault has given the CIS unit an improbable input or an input that is way beyond out of spec...

Example:
30% on a 126 is a Coolant Temp Sensor Fault. If the system is throwing this when key on engine off, then he and i suspect the CTS has gave the CIS-E a goofy value..CIS-E expected range x to y, and CTS provided something no where near that..

Thats our running theory right now, I'm going to change the CTS on my 420 and see if that clears the problem..

Lots of people having this same "problem".. Hopefully we'll get our heads around it.

Good to see the thread rejuvenated ...
 

Sounds like a sound judgement.

I'm going to start (soon) reading fault codes - I've concentrated on gearbox codes with excellent results.

More as it happens but it'll have to be after the weekend.

Thanks for response.

RayH

Ray, what car do you have?

I have a 1991 300CE-24 Sportline with Bosch KE Jetronic (CIS) injection and 5-speed 722.5 auto box. 350 K Kms on the clock.

I built a code reader (count the flashes, not too sophisticated!) and this enabled me to erase a gearbox fault that had put the 'box into some sort of safe mode. It's now performing as it should be with all 5 gears. Component cost of reader: €15.

I read the codes from the 16-pin (4 mm sockets) diagnostic connector close to the battery. Oddly, I've seem more information on the socket related to W129 cars than W124. Nonetheless, it is installed on a limited range of W124 cars.

I shall use the same reader to examine engine issues, possibly this weekend, weather permitting.

More as it happens.

RayH

If this helps at all, it's on my '91 300SE with the 103 engine, 49-state.

Key on engine off, but warm:
- DC = 50%, always has since 1991.
- Open the throttle between 10% and 90% open, DC = 10%.
- Open the throttle all the way and engage the under-pedal switch,
DC = 20%
- Press the air valve down, DC = 40%.

Crank the engine:
- DC switches momentarily from 50% to 70%, then back to 50%.
- After a few seconds, DC begins to fluctuate around 50%, as O2 sensor
comes in.

All the above makes sense to me:
Initial 50% without lambda control is normal, either without engine running, or before O2 sensor warms up.
Opening throttle with engine off should set a 10% fault code, which is throttle position fault.
Opening the air valve with the engine off should set a 40% fault code, which is an air valve fault.

So, I conclude those portions of my system are performing OK.
But I still have the 5-second hot-start chugging problem, which I have been chasing for 10 years.

DG
o