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Discussion Starter #21
... Regarding running behavior, however, a slightly further opened EHA with its current fluctuating around a mean value slightly below ‘0’ mA at idle, which is represented by a duty cycle fluctuating around a mean value slightly below 50%, is better. That has i.a. to do with the in post #1 mentioned better leaning than enriching capability of the EHA. 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. ...
I’d like to add some content to the above ‘i.a.’ :

Another reason for a duty cycle preferably below 50% is contamination.

Deposits can, for instance, narrow the 0.2 mm (~ 0.008“) wide vertical metering slits through which the fuel flows from the control plunger side into the upper chambers of the fuel distributor’s pressure differential valves. With the control plunger set to a slightly higher position via Lambda adjustment screw, these metering slits are a little wider open, which, as described in detail in post 1, in order to continue to receive confirmation of the correct air/fuel mixture (λ ~ 1) from the o2 sensor, is compensated via EHA control by more negative EHA current (lower duty cycle). Depending on the degree of contamination an adjustment to a rather low duty cycle might be beneficial for the engine’s running behavior.

However, if the degree of contamination in the fuel distributor requires a duty cycle below 35% to achive the best possible running behavior, and if a fuel distributor replacement or refurbishment does not come into consideration, changing the mechanical adjustment of the EHA’s baffle plate might be an option.
But, like refurbishing the fuel distributor, it requires adequate knowledge and significant care, patience and cleanness ! … I would not recommend to touch that tiny EHA adjustment screw if the EHA is looked at as a “black box” attached to another “black (gray) box”. :wink_2: … I’m thinking about creating a separate detailed thread about checking and changing the “EHA adjustment”, similar to this “duty cyle adjustment” thread.

Talking about contamination …
The KE-Jetronic is not overly enthusiastic about ethanol containing fuel, especially when the car sits a lot. I recommend not to put the car into hibernation for a couple of months with the fuel system filled with fuel containing more than 5% ethanol ! … If it’s unavoidable, I recommend at least to use a good and proper fuel additive, which I recommend in case of fuel containing more than 5% ethanol anyway, even if the car is driven long distance every day.
Ethanol containing fuel can lead to increased deposit forming and to acidification, which can lead to corrosion of the aluminium … and aluminum :) … parts of the KE-Jetronic.
There are fuel additives on the market which promise to prevent these effects and which, aside from the corrosion, even promise to reverse them … and I don’t say they don’t.

H.D.
 

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Hi,...i am a new user here. I do not believe in replacing parts on hunches. It has the subtle effect of distorting the decision making from that point forward, and in this case by possibly giving false credence to the notion of loss of holding pressure. This despite no testing having been undertaken to verify this.
 

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Hi,...i am a new user here. I do not believe in replacing parts on hunches. It has the subtle effect of distorting the decision making from that point forward, and in this case by possibly giving false credence to the notion of loss of holding pressure. This despite no testing having been undertaken to verify this.
You took the words right out of my mouth! Hang on... :confused: You did take the words out of my mouth!! :grin
 

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Discussion Starter #25
I’d like to reemphasize something I already addressed in post 2 of this thread.

In several threads I read that members simply readjusted the duty cycle because it was too high / low when they checked it. … Following my driving-along-the-road metaphor from post 1 that’s like loosening the steering wheel’s locknut and changing the wheel’s position because it’s not straight on a straight road, without caring about possible reasons like uneaven tyre pressure, sticking brake pistons, damaged steering mechanism, ...

Translated to the KE-Jetronic: If the duty cycle is out of tune, there’s a reason for that, and with a probability bordering on certainty it’s not related to the adjustment screw, unless someone fiddled around with it. Maybe there’s a fuel pressure problem, or a leaky CSV, or a false air leak, … … just to mention a few problems which influence the duty cycle ... and which would still be there after carelessly readjusting it ! ... :wink_2:

The duty cycle should primarily be seen as diagnostic information ... not only when it shows a static error code, but also when it fluctuates !
While that information is too often neglected, IMO, I always wanted access to it (plus other info) at the touch of a button anytime during driving or parking, and the picture below shows a device which provides that. I built it into the ashtray of my 300CE, when it was less than half as old as it is now.

Also, IMO, too often neglected is the information fuel pressure tests (particularly lower chamber pressure tests under specific conditions) can provide … best supplemented by simultaneous EHA current tests (of course, with the EHA adjustment screw not having been fiddled with !) … and, even better, also supplemented by partly simultaneous o2 sensor voltage tests.
These tests in addition to the duty cycle test, can be very informative … of course, with the duty cycle adjustment screw not having been touched, at least not after a problem started ! … They show whether the ECU is doing what it’s supposed to do … and whether it’s telling the diagnostic socket the truth about what it’s doing (in duty cycle language) ... and whether what it’s doing has respective effect on the EHA, hence on the lower chamber fuel pressure … and, consequently, on the air/fuel mixture … and, consequently, on the o2 sensor … and whether the ECU gets correct feedback from the o2 sensor.

I suggest to look at the KE-Jetronic as a playground for diagnostic thinking, instead of replacing parts which are not diagnosed faulty ! … increases the enjoyment of “golden era“ MBs. … And maybe you want to give a device like the one I made some thought … facilitates diagnosing problems with the OVP, FPR, CPS, o2-sensor, AFM-POT, TPS, CTS, and other parts immensely … especially if they’re intermittent ! … :wink_2:

H.D.

P.S.: I apologize in advance if I don‘t notice further posts / questions, which might happen because I‘m not receiving (required) email notifications from Benzworld anymore.
 

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I was directed to post #2 by another thread. The mixture adjustment procedure described in that post is inaccurate for some if not all M104 and M119 Jetronic engines. The post describes check procedures intended to ensure the accuracy of duty cycle measurements, and where the information is inaccurate it is impossible to complete those checks.

The information in this new post is based upon Mercedes' Startekinfo.com website and may not apply to all vehicles.

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. 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 a throttle switch or other input is in the wrong state for making a determination of the duty cycle being referenced to high or low voltage.

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.
 

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Discussion Starter #27
I was directed to post #2 by another thread. The mixture adjustment procedure described in that post ...
There is no “mixture“ adjustment procedure described in this thread. … For an explanation, see post #1.

What is described in this thread is the “Lambda control adjustment“ or “duty cycle adjustment“ … in Germany usually called “KE-Grundeinstellung“ ("KE basic setting").

... "Off" refers to low voltage, and that is the convention upon which Mercedes' documentation is based ...
In order to prevent other readers from confusion I repeat what I said in post #2 about MB’s … well - actually Bosch’s … definition of the duty cycle:
... In case of the KE-Jetronic the duty cycle value refers to the square wave voltage’s ‘off’-time ...
... According to Mercedes the duty cycle with a cool engine should be 30%, not 70% -- this fact may be inferred from reading this table ...
Maybe someone on the other side of the pond can commend on what he says about the duty cycle value with "ignition on / engine off" on U.S. 129's !?

... 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% ...
With all my duty cycle meters (analog and digital, including Bosch workshop meter) that is not the case. … And how could it, with the given nature of square wave voltage ... unless you use a meter that has an algorithm that converts the reading that way in that case. I have five duty cycle meters and none of them does that.
If you use a voltmeter and swap the leads, the values will be the same, only once without and once with a minus sign … according to the nature of square wave voltage.

... 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.
I repeat what I said in post #2:
... 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 ...
“intact” means “completely in order” … it refers also and especially to the fuel distributor and its parts and its cleanness.

Also see what else I said in that post:
... Above target values apply to an intact system (not only CIS) !
Generally problems relevant for the fuel combustion have an influence on the EHA control, hence on the duty cycle. Depending on the problem(s), the most suitable duty cycle could, for instance, be below 30% or above 70% ...
H.D.
 

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To avoid making a very long post I will respond to H.D.'s post #21 over the course of several replies.

I wrote:
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%.
H.D. replied:

With all my duty cycle meters (analog and digital, including Bosch workshop meter) that is not the case. … And how could it, with the given nature of square wave voltage.
It certainly is the case. Please see the 8-second video below.
.
 

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Discussion Starter #29 (Edited)
... It certainly is the case. ...
bobterry99, I told you already, that I don‘t like to see you alter my quotes ... see post 105 in this thread: http://www.benzworld.org/forums/r129-sl-class/2854594-wont-start.html

How can you say “It certainly is the case“ ? … I said that with my duty cycle meters it‘s not the case.

And you put a “.“ (period) in my quote behind “square wave voltage“ … which I did not put there. … Instead I continued with “... unless you use a meter that has an algorithm that converts the reading that way in that case.“ … which seems to be the case with the meter in that video.

bobterry99 ... don't forget what I said about further communication between you and me in the above-mentioned thread !

H.D.
 

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How can you say “It certainly is the case“ ? … I said that with my duty cycle meters it‘s not the case.
You are obviously correct -- I can not possibly know what would happen if you swapped the leads of your meters. I responded to the implication that duty cycle could not be "converted" and not your actual words.

don't forget what I said about further communication between you and me in the above-mentioned thread !
Am I suddenly in a parallel universe where Nazi Germany won WW2 and H.D. is mein Fuhrer? {...checking...} Good.

I will continue to post to this thread. I have to. The procedure you wrote has a fundamental mistake that at best makes it unworkable, and at worst could cause a member to misdiagnose a problem leading to a waste of time and money. More information is coming.
 

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Discussion Starter #31 (Edited)
... Am I suddenly in a parallel universe where Nazi Germany won WW2 and H.D. is mein Fuhrer? {...checking...} Good ...
That was a step too far, bobterry99 !

To other readers:

I will not further comment this completely unacceptable behavior. … But for better understanding of what‘s going on here I suggest to read the following thread at least up from post #100, or better up from post #45:
http://www.benzworld.org/forums/r129-sl-class/2854594-wont-start.html … That thread should explain enough.

And trust me on what I said in this thread … I was this side of 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.

I‘m confident that, if I discontinue this thread, the readers here will understand why. But in that case I can still be contacted for further information via PM.

H.D.
 

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That was a step too far, bobterry99 !
No, I simply stated a rhetorical question to make a point. You have mentioned that you lack experience with Internet forums. One thing to know is this: you can not control a thread or dictate to another member where they can post as you have repeatedly done with me.

Maybe someone on the other side of the pond can commend on what he says about the duty cycle value with "ignition on / engine off" on U.S. 129's !?
I wrote: "according to Mercedes the duty cycle with a cool engine should be 30%, not 70% -- this fact may be inferred from reading this table." There is no need to infer.

On STAR TekInfo there are documents providing engine "Test and Adjustment Data", and the one for the M119 and M104 engines are attached. Note in the very first table the specification for "on-off ratio" (duty cycle) for a cold engine with throttle closed is 30%. I believe a 12-valve 300SL with engine M103 -- a vehicle never sold in the U.S. -- would have a specification of 70%.
 

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Discussion Starter #33
... you can not control a thread or dictate to another member where they can post as you have repeatedly done with me ...
That‘s another example of this member‘s insincerity … which readers can assure themselves of by reading the thread the link in post #31 leads to … best, as I said, completely up from at least post #100 … there I expressed several times, due to his very unpleasant behavior, that I am not interested in further communication with him. ... I never dictated to him or to anybody else where they can post.

I will do what I can to avoid further communication with him, including in this thread, in which I will not further participate.

To all readers I repeat my offer from post #31: For further information regarding the topic of this thread, feel free to contact me via PM. ... :)

H.D.
 

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...I will not further participate [in this thread].
Occasionally I find myself replying to members seeking instructions how to check and adjust their mixture. I would like to direct them to your post #2, as I currently am aware of no single source of information that gives the correct procedure for M104 and M119 engines. Please return if for nothing more than to make a couple minor edits to the procedure and render it workable.

That‘s another example of this member‘s insincerity …
Now and again I perceive that you post with an aire of authoritarianism that is surreal to me. Perhaps it's just a consequence of our having different cultural and language backrounds. At any rate it isn't a problem for me, and I choose to minimize commenting on our personal differences and focus on our common interest in Mercedes cars.

In order to prevent other readers from confusion I repeat what I said in post #2 about MB’s … well - actually Bosch’s … definition of the duty cycle...
This thread caused me to question mixture adjustments that I had made to my cars. Should closed-throttle duty cycle be 30%? 70%? Prior to stumbling upon the test and adjustment documents I spent hours looking through the WIS and the Peachparts forum without finding a definitive answer. Along the way I discovered there is much confusion about duty cycle; it is a consequence of having different perspectives.

If a 10 ml glass holds 7 ml of water, then most people would describe the glass as being 70% full. But metaphorically, Mercedes would describe it as being 30% empty, as would H.D. and Bosch. Similarly, if a square-wave diagnostic signal is in a high-voltage state 70% of the time (Steve B. picture, attached), conventionally it is understood to have a duty cycle of 70%; yet Mercedes considers the percentage of time the signal is in its other (low-voltage) state, and to them the duty cycle is 30%.

Counter-intuitively, to get a Mercedes "glass empty" duty cycle measurement using a multimeter that reads duty cycle one typically puts the (+) lead on chassis ground and the (-) lead in X11 socket #3.
 

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There is no “mixture“ adjustment procedure described in this thread. … For an explanation, see post #1.
I read the first couple paragraphs of post #1 and see where you write:
"By changing the adjustment...which in case of a K-Jetronic (without lambda control) results in a changed ‘air/fuel mixture’, but - aside from the engine’s warm-up phase, or completely floored accelerator, or limp home mode - not in case of a KE-Jetronic! (Emphasis added by me.)​
"Aside from the engine's warm-up phase" is a significant caveat. Turning the "adjustment" screw clockwise will cause the engine to run richer during warm-up; turning it counter-clockwise leans it. Steve Brotherton regards this as a "mixture adjustment", and it establishes what he calls the engine's "basic" fuel mixture.

Once an engine becomes warm the fuel injection switches from "open-loop" to "closed-loop" mode of operation. In closed-loop a current in the range of -10 to +10mA is applied to the EHA to modify the basic mixture in accordance with the air/fuel ratio feedback signal provided by the oxygen sensor. H.D. refers to this as "lambda control".

If the basic fuel mixture is neither rich nor lean, the EHA current will average zero, and the lambda control will have the ability to correct for both a lean or rich mixture more or less equally. In this case Steve describes the lambda control as "centered".

Now, suppose the basic mixture is excessively lean to a degree that is far out of Mercedes' specification, and the closed loop EHA current is 8mA. The EHA is approaching a current limit (10mA, and the lambda control has little ability to correct for the mixture becoming further lean; however, it has a comparatively enormous capacity to compensate for it becoming leaner (-18mA of current available before reaching the opposite current limit). Consequently, the lambda control may be described as considerably imbalanced.

The adjustment procedure in post #2 is written with an emphasis on restoring an imbalanced lambda control to a centered or nearly-centered state. Thus it may be accurately described as a "lambda control" adjustment, but it is accomplished by and is a consequence of making mixture adjustments -- the basic mixture is made richer or leaner to cause the lambda control to respond in a manner that causes the EHA current to diminish and move toward zero.

Here is an imperfect analogy that may be useful. Suppose I have a thermostat in my home and a thermometer next to it. I am cold, so I adjust the thermostat to turn on the heat. My action increases the duty cycle of the furnace and causes hot air to blow into my home more frequently. The temperature in the house increases, and the column of mercury in the thermometer rises. Have I made a furnace adjustment, a temperature adjustment, a thermometer adjustment, or all three?
 

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...Maybe someone on the other side of the pond can commend on what he says about the duty cycle value with "ignition on / engine off" on U.S. 129's !?... H.D.
What Bobterry99 says is true for European 129s as well USA variants. At least it is true for mine in the UK. I have checked and confirmed that for a cold engine (<70deg C), ignition on-engine not running, the reported duty cycle (% off) is roughly 30%. See first pic.

...In case of the KE-Jetronic the duty cycle value refers to the square wave voltage’s ‘off’-time...
Unfortunately both WIS and StarTekInfo misleadingly refer to the duty cycle as the 'ON/OFF' ratio, whilst both you and Bobterry99 correctly state that the KE-Jetronic duty cycle value is actually the 'OFF/ON' ratio.

...With ignition switched on (engine not running) the duty cycle should be about 70% (California: 85%)...
These values are consistent with the WIS Diagnostic Manual for the W124, 126 and R129 300SL KE Jetronic engines, but WIS provides a different range of values for the R129 M119 and M104 engines.

For the R129, ignition on, engine not running, and a coolant temp between 70 and 100deg C, according to WIS, a ratio of 50 % would indicate that all input signals are in order. I have confirmed that this is true for my '91 500 SL. See second and third pics.

For a cold engine (<70 deg C) WIS infers that you would obtain a duty cycle of 30%, which I have also confirmed with my meter.

The WIS duty cycle ratios % for the R129 M104 and 119 CIS-E with ignition on, engine not running, are as follows: -
0% Not assigned.
I0% Idle speed contact throttle valve switch, full load/idle recognition (S29/2) open.
20% Idle speed contact throttle valve switch, full load/idle recognition (S29/2) closed.
30% Coolant temperature not between 70 and 100 °C.
40% Control plate of air flow sensor position indicator (B2) deflected.
50% Input signals in order.
60% Vehicle speed signal from electronic speedometer with maximum speed limiter (A1p8) recognized.
70% Starter signal terminal 50 recognized.
80% Drive mode engaged.
90% Current at electrohydraulic actuator (Y1) implausible.
I00% Not assigned.

...Static duty cycle:
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:

  • 0%: problem with the meter
    or diagnostic coupling (X11)
    or too rich setting (beyond the EHA’s ‘leaning limit’)
  • 10%: TPS (throttle position sensor), throttle fully closed signal
    or (if at 2.000 rpm) no/false supply voltage to POT (air flow potentiometer)
  • 20%: TPS, ‘throttle fully open’ signal
  • 30%: CTS (coolant temperature sensor)
  • 40%: no/false output voltage from POT
  • 50%: o2 sensor (aside from not having reached its operating temperature yet)
  • 60%: car speed signal (displayed during driving or engine still running after driving)
  • 70%: CPS (crankshaft position sensor)
    or EZL (electronic ignition module)
  • 80%: IATS (intake air temperature sensor)
  • 95%: micro switch of throttle linkage (6-cylinder engines)
  • 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’)...


  • Similarly the above list is ok for the relevant W124, 126 and R129 300SL KE Jetronic engines, but it is not consistent with WIS for the R129 M119 and M104 engines. According to WIS, the differences are: -

    80%: Fault in data interchange of EZL/AKR ignition control unit (N1/3) with KE control unit (N3).
    90%: Current to electrohydraulic actuator (Y1) implausible.
 

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"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."


Anyone got a picture of where this vacuum line is?
 

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This is a UK R129.

Pic 001. Under plastic cover (remove 2 screws).

Pic 002. Diagram of regen line (A). Arrow. Detach line from rubber elbow and plug for test.
 

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