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KE-Jetronic Lambda control (duty cycle check & adjustment)

45K views 77 replies 20 participants last post by  dolucasi 
#1 · (Edited)
Content deleted.

In case of interest in this for quick & targeted diagnosis and proper maintenance of CIS-E cars imperative topic, following This Thread in the sticky section will lead the reader to the identically named thread in the W126 forum.

H.D.
 
#4 ·
Pull off the vacuum line between the throttle valve and the regeneration valve of the fuel evaporation system at the regeneration valve and block it.
Hello.

I keep forgetting to do this. I invariably measure and set duty cycle with everything connected and the air filter in place.

Having said that, I am not disappointed with the results.

What am I likely to gain by disconnecting/blocking as you say? Is the duty cycle likely to be set higher? or lower? when everything's connected again.

Any guidance gratefully received and many thanks for your efforts.

RayH
 
#5 ·
With that vacuum line disconnected and blocked, you gain a more reliable duty cycle value.

Leaving it connected to the regeneration valve (thus to the activated carbon filter of the fuel evaporation system) can enrich the a/f mixture at the higher rev (2500 rpm), which leads to a lower duty cycle.

The disconnected vacuum line left open (not blocked) would, of course, be a false air leak causing a leaner a/f mixture, which leads to a higher duty cycle.
 
#6 ·
Hi H.D.
perfect explanation like usual

In my 300 CE-24 I had to change the EHA last year, because it was leaking. I messured a resistance of the coil from 19.8 Ohms.
In your Post 2, I think you have to correct the resitance value from KOhm to Ohm.

Thanks for a such good Post
Best regards from Germany
Marcel
 
#7 ·
Thank you for pointing that out, Marce107 … of course it should be ‘Ω’ instead of ‘kΩ’. I copied ‘kΩ’ from another document and forgot to delete the ‘k’.

I have corrected that in post #2

Thanks for your appreciation and best regards (from Germany too :))
 
#12 ·
... I would love to have that instrumentation in my astray as well. Much better use of the space.
Simply put, you "must" make more of those :)-))
Haha … you would indeed have appreciated it when you had your idle issue several weeks ago. The OVP’s intermittent ICV power supply problem would have leaped to your eye ’at the touch of one of its buttons’ ! ... :wink_2:

I really suggest to consider such a device … provides valuable information (not only) about the KE-Jetronic and speeds up diagnosis immensely … especially in case of intermittent problems.

And when you don’t use it you can switch it off and close the ‘ashtray’ ... however, in the initial period after installation you might find it interesting to keep it open and watch how Lambda control works during driving. … :wink_2:

H.D.
 
#15 ·
The mixture adjustment procedure in this thread was posted in the R129 forum and found to be unworkable for all U.S. cars. It's my guess that as written it won't work for any vehicle powered by the M104 or M119 engine, and that includes some W124 cars. The problem is a fundamental error that makes it impossible to complete the checks which are designed to ensure the accuracy of the duty cycle measurements.

The information in this new post is based upon Mercedes' Startekinfo.com website and may not apply to all cars with M104 and M119 engines.

In case of the KE-Jetronic the duty cycle value refers to the square wave voltage’s ‘off’-time.
"Off" refers to low voltage, and that is the convention upon which Mercedes' documentation is based. A way to distinguish whether a duty cycle reading references the signal's time at low voltage or high voltage is to take a measurement with the key on, the engine off, and a coolant temperature below 70 degrees Celsius. Along this line post #2 states:

With ignition switched on (engine not running) the duty cycle should be about 70% (California: 85%).
According to Mercedes the duty cycle with a cool engine should be 30%, not 70% -- this fact may be inferred from reading this table. To be clear, closed-throttle duty cycle is 70% for most W124s but is 30% for most if not all cars with M104 or M119 engines.

If a meter displays 70% its reference is wrong, and a simple remedy may be to swap the meter's leads to give a reading of 30%. Otherwise it is necessary to adapt to the incorrect reference by subtracting 100% from all duty cycle readings and then regard the negative result as a positive number. If a duty cycle other than 30 or 70 is displayed by a meter, then the throttle switch or other input is in the wrong state.

With ignition switched on (engine not running) the duty cycle should be about 70% (California: 85%).
If you’re using a voltmeter it should read 0.3 * Vp6 (California: 0.15 * Vp6).
If the duty cycle should be 30%, than a voltmeter should read .7 * Vp6.

A static (not fluctuating) duty cycle value with the engine running and the o2-sensor at operating temperature, indicates a problem according to the following list...
The list in post #2 is slightly inaccurate for an M119 or M104 engine. A more accurate and detailed reference which includes steps to troubleshoot the problem is found here at Startekinfo.

A closing comment:
A duty cycle at idle fluctuating around a mean value of about 47% or a little lower is usually a good choice for an intact KE-Jetronic in my experience.
Steve Brotherton is an engineer with perhaps more experience with Bosch Jetronic injection than anyone on the planet. Over on Peachparts.com he states that his personal preference is to adjust the mixture rich for a 40% duty cycle.
 
#21 · (Edited)
On STAR TekInfo there are documents providing engine "Test and Adjustment Data", and the one for variants of the M104 is attached. Its specification for "on-off ratio" (duty cycle) for a cold engine with throttle closed is 30%. Similar documents for the M119 and a variant of the M102 (M102.985) also specify 30%. Documents for all other listed engines specify 70% or 85% (California version).

So, for a W124 Mercedes specify closed-throttle duty cycle values of 30%, 70% and 85% -- the applicable specification depends on the particular vehicle and may not be known to the owner. However, all vehicles give an engine-off wide-open-throttle duty cycle of 20%, so I suggest this be used as a check to ensure that duty cycle measurements have the correct "glass empty" reference used by Mercedes.
 

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#22 ·
I want to announce that I discontinue my participation in this thread. Instead of explaning why, I refer to this thread in the 129 forum: http://www.benzworld.org/forums/r129-sl-class/2722145-ke-jetronic-lambda-control-duty-cycle.html … (read up from post #26). … In post #31 of that thread is another link for further clarification.

In case of doubts about the validity of the content of my posts here in this thread … it‘s well thought out and based on experiences with the engines in question here from the beginning. As a young design engineer I was personally involved in them before they came off the production lines.

For further information I can still be contacted via PM. … :)

H.D.
 
#27 ·
I'm confused by all this.

A lot of info, but hardly clear at all.

E.g. "Remove the plug from the adjustment tower (if it’s still in there)...."

How? Had to search other threads that you gotta basically hack the top of it to remove that ball bearing. What a stupid design by MB.


And still not clear for M104 engines. At idle, should it be 30% or 70%?


And: "With the throttle fully opened and the air sensor plate not deflected..."

Stupid question, but what is the air sensor plate?

These instructions seem a lot more clear to me: Beer, Bolts, Volts, and Bits: KE Jetronic Fuel Mixture Adjustment
 
#28 · (Edited)
There are various ways to remove that steel ball in the tower. I've read quite a few different approaches. The dealer must have done it in my white TE and this new-to-me TE had it already done by someone. I know that in my parts box is a small tower with a gasket, new. I don't remember how or why I acquired that. It would seem to me if the tower unscrews that easily, the attack would best be performed off the car.

In any event, a lot of people confuse how Mercedes chose to do the duty cycle, i.e., the percentage of the cycle they used during the pulse period. Even people buying duty cycle meters get confused at what they are looking at. I just use a big analog meter on volts, hooked up to #2 and #3. I figured out what my cycle voltage was (with a digital VOM) and did the formula. My voltage is 13.7 found between #2 and #6, if memory serves me correctly (that voltage never seems to change). I take the voltage I found between #2 & #3 (which averages 7 volts) and divide that by 13.7.....I get .51094891. Then for percentage, I do this; 1.0-.51094891=49%

Ideally, my needle will swing from 6.5 to 7.5 with 7 volts as the median average. When your needle swings like this, it indicates your O2 sensor is at least working. Cars with well worn AF potentiometers will not be able to hold your adjusted duty cycle reading for very long. These instruction are for the M103.

Kevin
 
#29 ·
my m103, someone had cut a slot on the side of the tower just below the balls 'equator', probably using a dremel cutoff disk or similar... this apparently allowed the ball/plug to be popped out, maybe with a small flat screwdriver?

the tower can't easily be unscrewed as it uses special screws with one way slots and breakaway heads.


the air sensor plate is the disk in the airflow meter that depresses with airflow... its directly above the throttle body. you can see it here ...

 
#30 ·
I haven't examined the in-car screws, as the ones with the extra tower are just Allens. I've seen the procedure with the cut on one side written up and it is, yes, to pry the ball up. Glad this was done before me on both TE's.

My original white TE screw adjustment was always rough....IOW, it was not smooth to turn-easy to do either too much or too little while adjusting. I sprayed some oil down there and it had no effect. This new-to-me TE is a little smoother, but it's a lot younger in miles.....

Kevin
 
#31 ·
"Connect the meter to the diagnostic coupling X11 port 3 and 2 (or ground)."


I get 100% w/that on my 90 300CE M104.980.

I get 80% w/the red in #1, and black in #3. Is that right?

And if so, is it really the "air intake temperature sensor"???

 
#32 ·
100%: problem with the meter
or diagnostic coupling (X11)
or ECU ‘N3’ (missing connection to voltage supply or to ground)
or OVP (overvoltage protection relay)
or o2 sensor signal (short to ground)
or too lean setting (beyond the EHA’s ‘enriching limit’)


New OVP, new O2 sensor...

How does one test the ECU 'N3'?

If I turn the DC clockwise, car runs very rough and then can't start. DC % doesn't change regardless.
 
#33 ·
Make sure your meter is measuring Duty Cycle not Hertz. Coincidentally the freq. of the signal is 100 (Hz).

Measure the actual voltage on the same pins in DC mode (not AC) as a sanity check. And report on:

(1) What is the frequency
(2) What is the duty cycle
(3) What is the DC voltage

Don't make any adjustments between these 3 measurements.
 
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