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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #1 (Edited)
Still seeing all the guessing games going on in case of CIS-E engine issues in all relevant sub-forums here at BenzWorld, I’d like to remind CIS-E car owners and, all the more, advising forum members not to ignore the most informative source of diagnostic information on CIS-E cars, the “Duty Cycle”.

Those who prefer targeted CIS-E troubleshooting .. and do not take delight in wasting time & money ;) .. I warmly recommend to take a close look at this THIS THREAD !

Most DIYers & professional mechanics think that the Duty Cycle just provides a few error codes and, at best, maybe a few hints about the injection system. But that’s far from it. Particularly in post #71 of the above thread I emphasized that not only injection system problems but everything that has an effect on the fuel combustion process (and more) has an effect on the Duty Cycle !;)

I‘d also like to reemphasize that, for reasons I explained in detail in the above thread, it is most warmly recommended not to simply readjust a deviated Duty Cycle via adjustment tower or, worse, fiddle around with the adjustment tower without even caring about the Duty Cycle ! … Look on these two things as inadvisable as, for instance, not keeping social distance (let alone without wearing a face mask) during a pandemic or as injecting desinfectant into the human body in order to try and kill a virus in it. … :rolleyes:

H.D.
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #2
Yesterday I was asked if ^this post is a dig at certain public office holders and/or their followers. I replied that it is a dig at expertise & facts rejecting dabblers. ;)

I continually see a lot of illogical CIS-E related info & advice being posted and not corrected by anyone here at BenzWorld (particularly in the W124, W201 & R107 forums). And I‘d like to save ‘golden era‘ MB owners from the frustration that is caused by the associated loss of time, money and engine health.

Of course, as the whole world can currently see, rejecting expertise & facts is not only a bad idea when it comes to the health of CIS-E engines. :rolleyes:

CIS-E related threads here at BenzWorld give me the feeling that my posts have either not been read or are not really understood or not trusted. Particularly advising members should try to understand at least what I said in the thread I mentioned in post 1. It will help to root out (even among professional mechanics) widespread misconceptions about the KE-Jetronic and to appreciate the diagnostic information that the Duty Cycle provides and to realize how counterproductive fiddling around with the Lambda adjustment screw (and the EHA adjustment screw) is. Plus, it will make diagnosis on CIS-E cars incomparably more targeted and quicker … and BenzWorld a much better place for help seeking CIS-E car owners.

H.D.
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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4,603 Posts
H.D., Are you familiar with the phrase "You can lead a horse to water but you can't make him drink."?

Please continue to share your expertise. That's all we can ask of anyone who had information to share. Some will listen, some will listen and act, and some will reject. That's the nature of the sharing of knowledge and experience.

I really enjoy your posts and find they open my eyes and understanding about the CIS-E system. For me, the system is definitely not intuitive but I'm enjoying the mind exercise of trying to grasp it. It's like learning a new language and I love it.
 

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Moderator
1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,778 Posts
Hello H.D.,

Having worked on CIS when new in 1974.. my thinking had some general ideas & theory, and after reading tor exacting threads, I realized I had more to learn..

Three years ago, I was about to have a tuner shop adjust my mixture on a dyno as I had recently had done a Tri-Ys to REMUS exhaust on my 500SEC.

I read one of your threads and had an 'Ahah!' moment regarding my fuel injection and left things well enough alone. Thank you.

I'm with LuckyMike with his quote: "You can lead a horse to water but you can't make him drink." That's just so true in many aspects of life & those we come in contact with.

You are making BW a much better place & we are grateful for your shared CIS-E expertise..

MBL
 

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Premium Member
1999 500SL, 1988 SEC
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1,353 Posts
HD, as I mentioned to others I have started printing (many) of your posts to assemble it into a book. Like you however I am pretty swamped but will get to it. One of the things I think that happens, and its not your fault, is that our archives are difficult to search and really hard to find what you want. What usually happens is when you do a search a whole posts pops up and you have to go through it which not only has your data, but all the chaff from others So what I think happens is someone simply puts out a new question and people chime in that really don't know. What should happen is that they do a detailed search. I am guilty of also not responding to tell those not knowledgeable to go elsewhere and look at your posts simply since I don't have all the technical knowledge to set them straight. I also get lazy. So please keep giving us the information, and one day you will have your own sticky with just what you have given us (moderators?).

i also think some of the younger generation want instant answers
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #6
Thanks Gentlemen.

H.D., Are you familiar with the phrase "You can lead a horse to water but you can't make him drink."?
Haha … yes, everybody around here is familiar with this metaphor. Horses enjoy great popularity here in my home town which hosts Germany's biggest anual international equestrian sports event (CHIO). The owner of one of the riding stables here said to me not long ago: “Auf den Rücken eines Pferdes gehören nur zwei Gefühle, Humor und Geduld“ (Only two emotions belong on the back of a horse, humor and patience). ;)

For me, the system is definitely not intuitive but I'm enjoying the mind exercise of trying to grasp it. It's like learning a new language
That is really a suitable analogy. Most advising members in car forums know a few CIS-E words, but hardly any CIS-E grammar that puts the words together in a meaningful way. Once this grammar is understood the system does become intuitive.

Of course, understanding this grammar takes more logical thinking than understanding that wearing face masks & keeping social distance should be a matter of course during a pandemic. Those who find it difficult to understand the latter, will certainly not understand the former and should not be entrusted with CIS-E car maintenance ... let alone with more important things. ;)

H.D.
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #7
So what I think happens is someone simply puts out a new question and people chime in that really don't know.
Yep … happens all the time, not only in forums. It‘s what I applied the “humor & patience“ to in my last post. It‘s a common problem, caused by too lean think/talk ratio.

On the other hand, this world would probably be a very quite place if people would talk only about things they know. In some countries, you‘d even constantly wonder if the head of state is still alive. :unsure:
 

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'82 500sec euro, '95 Ford F150
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My favorite saying goes like this:
“You can’t teach a pig to sing.
It wastes your time, and annoys the pig”

Thanks for your contribution HD.
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #9
Thanks for your contribution HD.
You‘re welcome roadhouse. … If only it would bear more fruit.

My favorite saying goes like this:
“You can’t teach a pig to sing.
It wastes your time, and annoys the pig”
Haha … reminds me to what my wife sometimes says to me (in Chinese) … “duì niú tán qín“ (playing the zither to a cow) :LOL: … a popular musical instrument in China, similar to the one in this video:


BTW, the conductor of ^this local orchestra was once a proud owner of a brand new & fully equipped 560SEL. :)
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #10 (Edited)
Haha … reminds me to what my wife sometimes says to me (in Chinese) … “duì niú tán qín“ (playing the zither to a cow) :LOL: … a popular musical instrument in China
Apropos “China“, that country has something in common with the KE-Jetronic. There is a number of widespread misconceptions about both.

For instance, the term “mixture regulating screw“ in MB‘s factury service manual leads many people to think that this screw is used to adjust CIS-E (KE-Jetronic) engines to run richer or leaner. But, as I explained in detail in This Thread, that is not the case. It was the case in the early days of CIS (K-Jetronic). The term “Gemischregulierschraube“ (mixture regulating screw), that was used in the K-Jetronic FSM, was misleadingly maintained in the KE-Jetronic FSM … like the term “CP“ (Communist Party) from the early days of the People‘s Republic of China (Mao Zedong‘s PRC) was misleadingly maintained when Deng Xiaoping took over … (coincidentally at about the same time when the KE-Jetronic was introduced :D). That leads many people to think that China‘s government (or society) is still communist. But that is not the case either, despite the fact that some political arsonists outside of China want people to think that. :rolleyes:

H.D.
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #11
I just skimmed a few threads about CIS-E engine problems mainly in other BW forums than this W126 forum. Many of these threads, after months of guessing & trying, did not lead to solving the problems. Although a quick Duty Cycle measurement should have been the first thing to do, it was done only in a few cases. But even in these cases the diagnostic information it provided was ignored. If the Duty Cycle was not in its supposed range (fluctuating in a range close to 50%), it was simply readjusted to that range via the adjustment tower … which is kind of like checking your watch and readjusting it, because you don‘t like it to be as late/early as your watch indicates. :rolleyes:

So again, in case of engine behavior issues, do not ignore the Duty Cycle … and certainly do not destroy its diagnostic information by simply readjusting it via adjustment tower !

Apparently, these basics are still practically unknown here at BW, especially in the W124, W201 & R107 sub-forums which are full of misinformation about this injection system … or “alternative information“. I heard this term on TV this week in a comment on somebody who was trying to explain that there is no need to wear a face mask in crowded situations. Watching the news has never caused my head to shake more often & to a larger angle as it has in the recent months. There is one good side to it, though. I had been feeling a little neck pain for some time when I turned my head 90° to the left. That pain has gone. … LOL

H.D.
 

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1991 560sec. 1991 560sel 1969 280SL
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1,333 Posts
We have moronic people here in the US who don’t believe in wearing a mask.
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #13
We have moronic people here in the US who don’t believe in wearing a mask.
Such people are everywhere … albeit not everywhere do they have role models for their ignorance in the highest public offices.

Anyway, be careful with “alternative information“ about the KE-Jetronic. There is an abundance of it in car forums, including BW. It‘s not rocket science, but understanding how it works & how to diagnose problems with engines that are equipped with it definitely takes more mental discipline than understanding that & why it is currently better to wear a mask near other people.
 

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Outstanding Contributor
1988 300CE
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1,573 Posts
Discussion Starter #14
If the Duty Cycle was not in its supposed range (fluctuating in a range close to 50%), it was simply readjusted to that range via the adjustment tower … which is kind of like checking your watch and readjusting it, because you don‘t like it to be as late/early as your watch indicates ...
… and I saw threads where people, partly referring to youtube videos, suggested to simply readjust the EHA if the difference between system pressure & lower chamber pressure is not according to specification, without caring about what‘s causing that deviated pressure difference, let alone fixing it. In Germany that is called “Flickschusterei“ … similar to the English word “kludge“.

When CIS-E cars left the factory, the Lambda adjustment screw and the EHA adjustment screw were hidden behind anti-tamper plugs for very good reasons. In most CIS-E cars that are still on the roads, the anti-tamper plug in the Lambda adjustment tower may not exist anymore, but the reason for it continues to exist … except for those who don‘t care about proper maintainance and quick & targeted troubleshooting based on reliable Duty Cycle readings. ;)
 

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H.D., I read your post from several years ago and it really helped me to understand the MB way of implementing the KE system in their cars. I was intrigued that you can get diagnostic codes by looking at the duty values. I was brought up in the VW andAudi world where diagnostics was more of a conventional cause and effect. In the VW world the EHA was called the differential pressure regulator and its value hovered around the 10ma center point. Later versions in Audi centered around the 0ma range when they integrated ignition into the fuel management.
When using the duty cycle on your gauge or meter you can simply reverse the connections to achieve the desired pos. or neg. trigger.
also in modern terms the duty cycle at idle and part throttle are nothing more than short term and long term fuel trims. Only today there are fuel tables within each range that allows for self tuning to keep the adjustments around a center point. Back then we did not have that and had to perform a “tune-up” after determining where air leaks or fuel leaks were happening.
 

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Outstanding Contributor
1988 300CE
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Discussion Starter #16
I was intrigued that you can get diagnostic codes by looking at the duty values.
The KE-Jetronic‘s diagnostic codes (the static Duty Cycle error codes) are only a small part of the diagnostic information that the Duty Cycle provides. Mainly the diagnostic information that the fluctuating Duty Cycle provides, if the Lambda adjustment screw & the EHA adjustment screw have not been unprofessionally fiddled around with, is what makes the Duty Cycle such a valuable provider of diagnostic information.

also in modern terms the duty cycle at idle and part throttle are nothing more than short term and long term fuel trims.
The information that the KE-Jetronic‘s fluctuating Duty Cycle provides with the warm engine running at any speed or load is by far not limited to fuel trims. … Besides, as I explained in detail in the thread I mentioned in post 1, it is erroneous to think that the engine is running leaner or richer when the Duty Cycle is fluctuating at a higher or lower range. ;)

H.D.
 

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The key is the fluctuations. When this is happening the engine is running at its optimum. The percentage does reveal how far outside of the desired set point for the given temp and load. I know on the VW side the potentiometer on the airflow plate was input to the ECU as to how fast the plate was moving and that would result in a temp increase in the actuator current. More pronounced when cold much like an accelerator pump on a carb. I will go back and read more of your posts. I believe the w126 I’m driving is a California emissions spec car. For 1986 what must I do to set it into duty cycle mode? What did Mercedes do to comply with CA diagnostics? I know the W124 has a diagnostic module but I’m not sure what it provides?
 

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Outstanding Contributor
1988 300CE
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Discussion Starter #18
The key is the fluctuations. When this is happening the engine is running at its optimum. ...
A fluctuating Duty Cycle tells you that the CIS-ECU is receiving (hopefully reliable) o2 sensor input and that it is reacting on it with corresponding EHA current. But that does not necessarily mean that “the engine is running at its optimum“. As I explained in the thread I mentioned in post #1, the range of the (reliable!) fluctuating Duty Cycle under all kinds of engine running conditions can point to many (not only air/fuel mixture related) problems. ;)

I will go back and read more of your posts.
(y) … Don‘t leave out the thread I mentioned in post 1. ;)

I believe the w126 I’m driving is a California emissions spec car. For 1986 what must I do to set it into duty cycle mode? What did Mercedes do to comply with CA diagnostics? I know the W124 has a diagnostic module but I’m not sure what it provides?
^These, country/state dependent, details are explained on MB‘s “WIS“ (Workshop Information System) CD. A lot of that CD‘s content is also circulating as PDF files on the internet. If you need further help on that, please start a seperate thread about it. :)

H.D.
 
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