Seeking confirmation: Mercedes and duty cycle - PeachParts Mercedes-Benz Forum

Stretch · #1 11-23-2015, 07:33 AM

G'day Folks,

I'm having a miserable time trying to diagnose a now consistent stalling problem on my W201.

{
After you drive the car the engine wants to stall when you dip the clutch. Start the car and rev from idle it is fine. I can't reproduce the fault that way.
}

So Looking at the WIS / FSM information I have for this piece of **** I see that there are two ways of measuring fault codes.

Way #1 =>

Blip code tester. Plug it in. Get a red light. Press the button for about 2 seconds - count the error codes as they come back.

I always get one blip = everything OK mate!

Way #2 =>

Ignition on - engine not running.

Measure duty cycle at X11 port (On W201 next to ABS pump left hand wheel arch engine bay)

Pin #2 is ground

Pin #3 is output from O2 sensor => duty cycle

For this I measure a 30% (29.8%) error code.

############

Checking in the WIS / FSM information I've got that says temperature sender (from coolant). There is nothing wrong with this part of the car - I am totally sure about this. I get a reasonable resistance reading from the sender and I can trace this resistance all the back to the ECU plug. (Between pins7 and 21 on the ECU plug)

############

HOWEVER (!)

I remember reading somewhere that Mercedes "duty cycle" is the inverse of normal duty cycle. So 50% is always 50% but 30% is 70% (20 is 80 - 10 is 90 etc etc etc)

Can some one confirm?

Anyone know?

Frank Reiner · #2 11-23-2015, 09:39 AM

Quote:

Originally Posted by Stretch

G'day Folks,

Way #2 =>
Ignition on - engine not running.
Measure duty cycle at X11 port (On W201 next to ABS pump left hand wheel arch engine bay)
Pin #2 is ground
Pin #3 is output from O2 sensor => duty cycle
For this I measure a 30% (29.8%) error code.

For this test the engine should be running at idle.

############
Checking in the WIS / FSM information I've got that says temperature sender (from coolant). There is nothing wrong with this part of the car - I am totally sure about this. I get a reasonable resistance reading from the sender and I can trace this resistance all the back to the ECU plug. (Between pins7 and 21 on the ECU plug)
############

HOWEVER (!)
I remember reading somewhere that Mercedes "duty cycle" is the inverse of normal duty cycle. So 50% is always 50% but 30% is 70% (20 is 80 - 10 is 90 etc etc etc)
Can some one confirm?

Anyone know?

If the meter leads are reversed, then you should see inverted ratios.

Stretch · #3 11-23-2015, 10:11 AM

Quote:

Originally Posted by Frank Reiner

If the meter leads are reversed, then you should see inverted ratios.

Really? I'll check that tomorrow.

I thought the meter would compare steady with fluctuating:- in other words even if I had got the negative (earth) mixed up the meter would "know"

TnBob · #4 11-23-2015, 01:09 PM

I saw the inversion waaay back when. Using 2 and 3 ports, readings went from 90 / 10 to 10 / 90

Stretch · #5 11-23-2015, 01:15 PM

I'm sure pin 2 on the X11 diagnostic plug is -tve and pin 3 is the +tve signal though

That's what gives me an ignition on - engine not running - fault "code" of 30%.

Problem is that doesn't agree with the fault finding I've made of the connections and the coolant sensor.

Now if 30% on my meter meant 70% in "Mercedes land" I'd be much happier believing that!

Stretch · #6 11-23-2015, 01:43 PM

Hmmm

Late Model CIS-E Diagnostic / Duty Cyle Help

BOSCH KE3-JETRONIC MIXTURE ADJUSTMENT

Confirmed?

Frank Reiner · #7 11-23-2015, 07:15 PM

Stretch:

As a check on the position of the duty cycle scale of your meter, consider using voltages as outlined in the Mixture Adjustment link that you posted above. That way you can determine if 30% = 30%, or if 30% = 70%.

Stretch · #8 11-24-2015, 06:29 AM

Oh yes - wood and trees again...