KE-Jetronic Lambda control (duty cycle check & adjustment)
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If by “limited“ you mean “small“, I recommend to reread the chapter “Basics“ in post 1. Towards the end of that chapter I said:
“From the above it may also become clear that the air/fuel mixture can not only be ‘micro-adjusted’ (to ‘λ ~ 1 +/- 0.02’) via EHA control, as often assumed, but also ‘macro-adjusted’ ...”
As I explained there in detail, the tiny fluctuating adjustments via EHA control to the (stoichiometric) Lambda range of ‘λ ~ 1 +/- 0.02’ equate, in case of non-ethanol fuel, to an air/fuel mass ratio range of about 14.4 - 15 (14.7 +/- 0.3). That’s a micro-adjustment range of +/- 2%.
But Lambda control is able to correct the air/fuel mass ratio back to that stoichiometric range via EHA control by (in chapter “Basics“ described) macro adjustments of up to about +20% (e.g. in case of a leaking CSV) or about -20% (e.g. in case of a vacuum leak).
During acceleration within the warm-up phase the mixture can be enriched via EHA control by more than 20%. During overrun shut-off the amount of injected fuel is reduced via EHA control by 100% (zero fuel).
H.D.
Great, interesting.
So when the EHA is at "at rest"/volt-less the mixture should be close to 14.7 in "ideal" conditions? (Engine at idle, operating temp, etc.)
Does the KE also adjust for difference in altitude (barometric pressure) via the EHA, or only via the resulting change in mixture measured at the O2 sensor?
Sent from my MAR-LX1M using Tapatalk
So when the EHA is at "at rest"/volt-less the mixture should be close to 14.7 in "ideal" conditions? (Engine at idle, operating temp, etc.)
Does the KE also adjust for difference in altitude (barometric pressure) via the EHA, or only via the resulting change in mixture measured at the O2 sensor?
Sent from my MAR-LX1M using Tapatalk
Yes … in case of non-ethanol fuel … or a little lower, like 14.2 - 14.3, which is the case after adjustment of the fluctuating EHA current to a mean value of about minus 0.6 mA, unless there‘s a fuel combustion affecting problem.
Yes, it does … either directly & more precisely if the car is equipped with an altitude sensor, or indirectly & less precisely if it‘s not equipped with an altitude sensor.
In the latter case it‘s the o2 sensor alone that induces adjustments. It senses any difference in the ratio between the amount of residual oxygen in the exhaust gas and the amount of oxygen in the ambient air … thus including the effect that different altitudes have on that ratio.
Without any of these sensors (working), the engine would run richer at higher altitudes, because the air‘s lower mass per volume at higher altitudes causes a bigger stroke of the FD‘s control piston per mass of intake air, leading to richer air/fuel mixture. … With (correct) respective sensor input that is corrected via EHA control.
As mentioned in post 51 (and contrary to common believe :wink_2
, o2 sensors can not really “measure the air/fuel mixture“. They generate voltage solely depending on the above-mentioned ratio between the amount of residual oxygen in the exhaust gas and the amount of oxygen in the ambient air … and that ratio depends not only on the air/fuel mixture, but on everything that has an effect on the fuel combustion !Only if there are no fuel combustion affecting problems (and no holes in the exhaust pipe :wink_2
a healthy o2 sensor‘s voltage of 450 mV is a reliable representative of stoichiometric air/fuel mass ratio. … That is usually overlooked but important to consider for proper troubleshooting !H.D.
Health & Diagnosis of CIS-E engines
I‘d like to point once again to two things that are still frequently reported or, worse, recommended here at BenzWorld:
1) Fiddling around with the adjustment tower without caring about Duty Cycle or EHA current readings.
2) Readjustment of deviated Duty Cycle (respectively EHA current) readings via the adjustment tower instead of by taking care of the cause(s) of the deviation.
The fact that the former is an absolute no-no should go without saying. But let me illustrate once more what you actually do when you do the latter and why it is a bad idea to do that, using a metaphor:
Let‘s say you usually wake up at about 7:00 AM. But one day you wake up later. You look at your watch and it reads 8:20. You think that‘s not right, it should read about 7:00. The question what's causing the deviated reading, doesn‘t cross your mind. You just set it back to 7:00. That may make things feel right for you again, but you‘ll be late for work. You‘ll probably not loose your job because of being late once, but if you leave your watch set back to that, in your eyes correct, time reading and don‘t take care of the cause of the deviated reading, namely your oversleeping, there will be consequences.
Translated to the KE-Jetronic, that‘s similar to what you do when you simply readjust a deviated Duty Cycle from fluctuating around say 80% to fluctuating around 50% via adjustment screw without taking care of the cause of the deviated reading, just because that‘s what you think it should read. That may make things feel right for you again, but with Lambda control inactive and the throttle opened, the engine will run too rich now. You will not loose the engine because of too rich mixture during one warm-up phase, but if you leave the Duty Dycle set to 50% and don‘t take care of the cause of its deviation to 80%, like e.g. a vacuum leak, there will be consequences ! … It would be much better to fix the vacuum leak, instead of masking it by simply readjusting the Duty Cycle via adjustment screw … If there are no other fuel combustion affecting problems and the adjustment screw has not been messed with, fixing the vacuum leak will automatically make the Duty Cycle fluctuate close to 50% again.
The same applies to simply readjusting a deviated Duty Cycle from fluctuating around say 30% to fluctuating around 50% via adjustment screw. Things may feel right for you again, but the engine will suffer in that case too. If you leave the Duty Cycle set to 50% and don‘t take care of the cause of its deviation to 30%, like e.g. one or several worn injector(s), the engine will run too rich in the cylinder(s) with the worn injector(s) and too lean in all other cylinders at any engine speed, with & without active Lambda control ! … For the same reason as fixing the above vacuum leak, it would be much better to replace the worn injector(s) instead.
(Note that vacuum leaks or worn injectors are only two of many examples of problems that cause deviated duty cycle readings !)
Always readjust a deviated Duty Cycle primarily by fixing what‘s causing its deviation … not by fiddling around with the adjustment tower !
Only after all potential causes for the deviation have been checked and, if necessary, fixed, the Duty Cycle should be readjusted via Lambda adjustment screw according to the procedures in post #2.
This is not only better for the engine, but also the only way to maintain the fluctuating Duty Cycle as the (mostly unknown) full-featured provider of reliable & valuable diagnostic information it‘s supposed to be … (like your watch is supposed to reliably inform you about the time of the day). … It makes troubleshooting a lot quicker & easier. Most DIYers & mechanics think that only a static Duty Cycle provides diagnostic information (in the form of error codes). But that‘s an error. The fluctuating Duty Cycle is even a lot more informative … unless the Lambda adjustment screw (and/or the EHA adjustment screw) has been unprofessionally fiddled around with !
Unfortunately, both ^these aspects (the benefit for the engine‘s health and the benefit for diagnosis) are and probably will continue to go mostly unheeded … not only in car forums, but even in “professional“ garages. Fixing problems will probably mostly continue to be tried by guessing & throwing parts at them and by fiddling around with the Lambda (& EHA) adjustment screw(s), regardless of the consequences.
But maybe & hopefully, some readers will give this thread a little more thought and not further neglect the richest and so easy to check diagnostic information that their CIS-E cars constantly provide .. the Duty Cycle .. let alone falsify it by fiddling around with the adjustment tower !
H.D.
P.S.: Please note what I said at the end of post #38.
I‘d like to point once again to two things that are still frequently reported or, worse, recommended here at BenzWorld:
1) Fiddling around with the adjustment tower without caring about Duty Cycle or EHA current readings.
2) Readjustment of deviated Duty Cycle (respectively EHA current) readings via the adjustment tower instead of by taking care of the cause(s) of the deviation.
The fact that the former is an absolute no-no should go without saying. But let me illustrate once more what you actually do when you do the latter and why it is a bad idea to do that, using a metaphor:
Let‘s say you usually wake up at about 7:00 AM. But one day you wake up later. You look at your watch and it reads 8:20. You think that‘s not right, it should read about 7:00. The question what's causing the deviated reading, doesn‘t cross your mind. You just set it back to 7:00. That may make things feel right for you again, but you‘ll be late for work. You‘ll probably not loose your job because of being late once, but if you leave your watch set back to that, in your eyes correct, time reading and don‘t take care of the cause of the deviated reading, namely your oversleeping, there will be consequences.
Translated to the KE-Jetronic, that‘s similar to what you do when you simply readjust a deviated Duty Cycle from fluctuating around say 80% to fluctuating around 50% via adjustment screw without taking care of the cause of the deviated reading, just because that‘s what you think it should read. That may make things feel right for you again, but with Lambda control inactive and the throttle opened, the engine will run too rich now. You will not loose the engine because of too rich mixture during one warm-up phase, but if you leave the Duty Dycle set to 50% and don‘t take care of the cause of its deviation to 80%, like e.g. a vacuum leak, there will be consequences ! … It would be much better to fix the vacuum leak, instead of masking it by simply readjusting the Duty Cycle via adjustment screw
… If there are no other fuel combustion affecting problems and the adjustment screw has not been messed with, fixing the vacuum leak will automatically make the Duty Cycle fluctuate close to 50% again. The same applies to simply readjusting a deviated Duty Cycle from fluctuating around say 30% to fluctuating around 50% via adjustment screw. Things may feel right for you again, but the engine will suffer in that case too. If you leave the Duty Cycle set to 50% and don‘t take care of the cause of its deviation to 30%, like e.g. one or several worn injector(s), the engine will run too rich in the cylinder(s) with the worn injector(s) and too lean in all other cylinders at any engine speed, with & without active Lambda control ! … For the same reason as fixing the above vacuum leak, it would be much better to replace the worn injector(s) instead.
(Note that vacuum leaks or worn injectors are only two of many examples of problems that cause deviated duty cycle readings !)
Always readjust a deviated Duty Cycle primarily by fixing what‘s causing its deviation … not by fiddling around with the adjustment tower !
Only after all potential causes for the deviation have been checked and, if necessary, fixed, the Duty Cycle should be readjusted via Lambda adjustment screw according to the procedures in post #2.
This is not only better for the engine, but also the only way to maintain the fluctuating Duty Cycle as the (mostly unknown) full-featured provider of reliable & valuable diagnostic information it‘s supposed to be … (like your watch is supposed to reliably inform you about the time of the day). … It makes troubleshooting a lot quicker & easier. Most DIYers & mechanics think that only a static Duty Cycle provides diagnostic information (in the form of error codes). But that‘s an error. The fluctuating Duty Cycle is even a lot more informative … unless the Lambda adjustment screw (and/or the EHA adjustment screw) has been unprofessionally fiddled around with !
Unfortunately, both ^these aspects (the benefit for the engine‘s health and the benefit for diagnosis) are and probably will continue to go mostly unheeded … not only in car forums, but even in “professional“ garages. Fixing problems will probably mostly continue to be tried by guessing & throwing parts at them and by fiddling around with the Lambda (& EHA) adjustment screw(s), regardless of the consequences.
But maybe & hopefully, some readers will give this thread a little more thought and not further neglect the richest and so easy to check diagnostic information that their CIS-E cars constantly provide .. the Duty Cycle .. let alone falsify it by fiddling around with the adjustment tower !
H.D.
P.S.: Please note what I said at the end of post #38.
Apropos “EHA adjustment screw“ … I also still frequently see adjustments via this screw recommended here at BenzWorld … sometimes with reference to YouTube videos.
I advise against blindly following these recommendations. They‘re usually solely based on fuel pressure readings, saying the adjustment should be done if the difference between LCP (Lower Chamber Pressure) & SP (System Pressure) is not ~0.4 bar … often without mentioning test conditions and, worse, always without mentioning any of the other things that should always be checked before thinking of touching the EHA adjustment screw at all.
Please note what I said regarding ”EHA adjustment” in post #59.
H.D.
No … neither via Lambda adjustment screw nor via EHA adjustment screw. The criteria for adjustments via Lambda adjustment screw I described extensively & insistently (
) in this thread. Please mind that, besides what I said in post #59, I‘d like to keep details regarding adjustments via EHA adjustment screw out of this Lambda control thread.Anyway, the most important recommendation regarding both of these adjustments screws is … Do not touch them ! … unless you know when to touch them.
Thank you H.D. for you advice and information here - extremely helpful!
Duty Cycle Interpretation
In post #60 I said that I‘ll post detailed guidance on Duty Cycle interpretation when I have a little more time. That was before the forum was downgraded last August, in the course of which several extensive posts of mine disappeared, keeping me back from continuing this thread as extensively as I planed to. But I don‘t want to leave it as unfinished as it is now. Since proper interpretation of, particularly, the fluctuating Duty Cycle is still quite uncharted territory (not only) here at BenzWorld, here‘s a general short guide.
Earlier in this thread I said that, contrary to widespread believe, it is erroneous to think that the engine is running leaner when the Duty Cycle is fluctuating at a higher range or that it is running richer when it’s fluctuating at a lower range. This misconception is one of the biggest obstacles to proper CIS-E diagnosis. … If the Duty Cycle is fluctuating (with a frequency as described under “Check procedures“ in post #2), no matter whether it‘s fluctuating in a high or in a low range, Lambda control is active … meaning that the CIS-ECU is receiving o2 sensor voltage fluctuating between about 100 and 800 mV (in case of a healthy o2 sensor) and that it is sending a fluctuating current in positive or negative direction through the EHA in order to keep receiving o2 sensor voltage fluctuating between 100 and 800 mV … which is the only thing that, regarding Lambda control, the CIS-ECU cares about … and which is commonly regarded as a representative of the air/fuel mixture.
However, the o2 sensor voltage is not a “reliable" representative of the air/fuel mixture. As I explained in post #1, the o2 sensor voltage depends solely on the ratio between the content of residual oxygen in the exhaust gas inside of the exhaust pipe and the content of oxygen in the ambient air outside of the exhaust pipe. That ratio is determined by the fuel combustion process. And that process depends not only on the air/fuel mixture. It depends on a number of other things too. So the whole fuel combustion process determines the amount of residual oxygen in the exhaust gas … hence the o2 sensor voltage … hence the EHA current … hence the lower chamber fuel pressure … hence the Duty Cycle. …
^This should bring, Duty Cycle affecting, things to mind that even most professional mechanics are not aware of and that are practically always overlooked here at BenzWorld, including things that have nothing to do with the fuel injection system. … (Once I tried to draw attention to that in the W124 forum to no avail. But I count on more interest & attention here in the W126 forum. )
The understanding of these things is the main key to proper CIS-E diagnosis. So, next time when there‘s an engine behavior issue, check the Duty Cycle, and if it fluctuates in a higher or in a lower range - (before even remotely thinking about touching the adjustment screw !) - ask yourself the following questions in the following order:
Just keep in mind that Lambda control reacts on anything that has an effect on the fuel combustion process … and don‘t forget that there might be a problem with the Lambda control function chain (o2 sensor → CIS-ECU → EHA → FD) itself, which can all be tested ... or that a hole in the exhaust pipe might be fooling the o2 sensor and, consequently, the CIS-ECU … etc.
Again … my main objective with this Lambda control thread is to convince readers
I hope that what I‘ve posted in this thread will eventually be given greater attention, reducing the number of time & money wasting CIS-E related guessing games that are still going on here at BenzWorld and leading to much more targeted & quicker troubleshooting & avoidance of unnecessary part replacements … and to greater appreciation of the KE-Jetronic. ... After all, this remarkable & underestimated piece of mechanical engineering is one of the most typical representatives of the spirit ‘golden era‘ MB‘s were designed with … as knowledgeable enthusiasts know very well.
H.D.
In post #60 I said that I‘ll post detailed guidance on Duty Cycle interpretation when I have a little more time. That was before the forum was downgraded last August, in the course of which several extensive posts of mine disappeared, keeping me back from continuing this thread as extensively as I planed to. But I don‘t want to leave it as unfinished as it is now. Since proper interpretation of, particularly, the fluctuating Duty Cycle is still quite uncharted territory (not only) here at BenzWorld, here‘s a general short guide.
Earlier in this thread I said that, contrary to widespread believe, it is erroneous to think that the engine is running leaner when the Duty Cycle is fluctuating at a higher range or that it is running richer when it’s fluctuating at a lower range. This misconception is one of the biggest obstacles to proper CIS-E diagnosis. … If the Duty Cycle is fluctuating (with a frequency as described under “Check procedures“ in post #2), no matter whether it‘s fluctuating in a high or in a low range, Lambda control is active … meaning that the CIS-ECU is receiving o2 sensor voltage fluctuating between about 100 and 800 mV (in case of a healthy o2 sensor) and that it is sending a fluctuating current in positive or negative direction through the EHA in order to keep receiving o2 sensor voltage fluctuating between 100 and 800 mV … which is the only thing that, regarding Lambda control, the CIS-ECU cares about … and which is commonly regarded as a representative of the air/fuel mixture.
However, the o2 sensor voltage is not a “reliable" representative of the air/fuel mixture. As I explained in post #1, the o2 sensor voltage depends solely on the ratio between the content of residual oxygen in the exhaust gas inside of the exhaust pipe and the content of oxygen in the ambient air outside of the exhaust pipe. That ratio is determined by the fuel combustion process. And that process depends not only on the air/fuel mixture. It depends on a number of other things too. So the whole fuel combustion process determines the amount of residual oxygen in the exhaust gas … hence the o2 sensor voltage … hence the EHA current … hence the lower chamber fuel pressure … hence the Duty Cycle. …
^This should bring, Duty Cycle affecting, things to mind that even most professional mechanics are not aware of and that are practically always overlooked here at BenzWorld, including things that have nothing to do with the fuel injection system.
… (Once I tried to draw attention to that in the W124 forum to no avail. But I count on more interest & attention here in the W126 forum. )The understanding of these things is the main key to proper CIS-E diagnosis. So, next time when there‘s an engine behavior issue, check the Duty Cycle, and if it fluctuates in a higher or in a lower range - (before even remotely thinking about touching the adjustment screw !) - ask yourself the following questions in the following order:
- What EHA current leads to this Duty Cycle ?
- What o2 sensor voltage leads to this EHA current ?
- What level of residual oxygen in the exhaust gas (high or low) leads to this o2 sensor voltage ?
- What fuel combustion affecting problem(s) can lead to this level of residual oxygen in the exhaust gas ?
Just keep in mind that Lambda control reacts on anything that has an effect on the fuel combustion process … and don‘t forget that there might be a problem with the Lambda control function chain (o2 sensor → CIS-ECU → EHA → FD) itself, which can all be tested ... or that a hole in the exhaust pipe might be fooling the o2 sensor and, consequently, the CIS-ECU … etc.
Again … my main objective with this Lambda control thread is to convince readers
- to check the Duty Cycle more often in order too see how the system (not only the injection system) is doing, respectively to see what‘s wrong with it, because it‘s the most informative source of diagnostic information available on CIS-E cars and so easy to check.
- and to touch the Lambda (as well as the EHA) adjustment screw way less often (if at all !) in order not to falsify/destroy the Duty Cycle‘s diagnostic information and in order not to cause damage to the engine. See what I said about that particularly in posts #39 and #65 !
I hope that what I‘ve posted in this thread will eventually be given greater attention, reducing the number of time & money wasting CIS-E related guessing games that are still going on here at BenzWorld and leading to much more targeted & quicker troubleshooting & avoidance of unnecessary part replacements … and to greater appreciation of the KE-Jetronic.
... After all, this remarkable & underestimated piece of mechanical engineering is one of the most typical representatives of the spirit ‘golden era‘ MB‘s were designed with … as knowledgeable enthusiasts know very well.H.D.
Measuring the Duty Cycle
Fortunately, sometimes in case of issues with CIS-E engines, interest in their most informative source of diagnostic information, the “Duty Cycle“, does appear here at BenzWorld. … Since, however, there is still frequently confusion about it and how to measure it, here are a few more details about it.
As described in post #1, the “Duty Cycle“ refers to a square wave voltage signal which jumps from ‘battery voltage‘ to ‘zero volt‘, stays there for a moment, then jumps back to ‘battery voltage‘ and stays there for a moment. <This describes ‘1 period‘ of this signal, which repeats itself about 100 times per second (f ≈ 100 Hz).
“Duty Cycle“ is another word for the ratio, that in MB‘s service manual is called “on/off ratio“. In case of the KE-Jetronic‘s diagnostic signal, however, it is actually an“off/on ratio“, because it refers to the percentage of the signal‘s OFF-time (‘zero volt‘ time). Thus it is most conveniently measured with a duty cycle meter whose reading refers to the OFF-time. … Most duty cycle meters / multimeters with duty cycle function, however, refer to the ON-time and would misleadingly read “20%“ in case of a signal that is ‘zero volt‘ over 80% of the time !
An analog meter is better suited than a digital one, because it makes reading the fluctuating Duty Cycle significantly easier. With the warm engine running (and a healthy o2 sensor), the Duty Cycle fluctuates (respectively, is supposed to fluctuate) between two values about every second at idle speed and about every half a second at 2500 rpm.
If you use a multimeter and it reads (close to) “100“, make sure you‘re not measuring the signal‘s frequency (in Hz) instead of its Duty Cycle (in %) !
In case of uncertainty whether your meter‘s duty cycle reading refers to the OFF-time or the ON-time, just use a voltmeter or a multimeter and measure the following voltages:
Always measure Vp3 and Vp6 (!) … (with ‘ignition on‘, with ‘engine running‘, …) !
Then convert them into “Duty Cycle“ according to this formula: Duty Cycle [%] = (1 - Vp3/Vp6) * 100
Example of a measurement with the warm engine running at idle speed:
Instead of doing ^this math, here is a handy alternative:
The attached example is done with the above measured Vp6 & Vp3.
H.D.
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Fortunately, sometimes in case of issues with CIS-E engines, interest in their most informative source of diagnostic information, the “Duty Cycle“, does appear here at BenzWorld.
… Since, however, there is still frequently confusion about it and how to measure it, here are a few more details about it.As described in post #1, the “Duty Cycle“ refers to a square wave voltage signal which jumps from ‘battery voltage‘ to ‘zero volt‘, stays there for a moment, then jumps back to ‘battery voltage‘ and stays there for a moment. <This describes ‘1 period‘ of this signal, which repeats itself about 100 times per second (f ≈ 100 Hz).
“Duty Cycle“ is another word for the ratio, that in MB‘s service manual is called “on/off ratio“. In case of the KE-Jetronic‘s diagnostic signal, however, it is actually an“off/on ratio“, because it refers to the percentage of the signal‘s OFF-time (‘zero volt‘ time). Thus it is most conveniently measured with a duty cycle meter whose reading refers to the OFF-time. … Most duty cycle meters / multimeters with duty cycle function, however, refer to the ON-time and would misleadingly read “20%“ in case of a signal that is ‘zero volt‘ over 80% of the time !
An analog meter is better suited than a digital one, because it makes reading the fluctuating Duty Cycle significantly easier. With the warm engine running (and a healthy o2 sensor), the Duty Cycle fluctuates (respectively, is supposed to fluctuate) between two values about every second at idle speed and about every half a second at 2500 rpm.
If you use a multimeter and it reads (close to) “100“, make sure you‘re not measuring the signal‘s frequency (in Hz) instead of its Duty Cycle (in %) !
In case of uncertainty whether your meter‘s duty cycle reading refers to the OFF-time or the ON-time, just use a voltmeter or a multimeter and measure the following voltages:
- “Vp3“ (between ports 3 & 2 of the round X11 socket)
- “Vp6“ (between ports 6 & 2 of the round X11 socket)
Always measure Vp3 and Vp6 (!) … (with ‘ignition on‘, with ‘engine running‘, …) !
Then convert them into “Duty Cycle“ according to this formula: Duty Cycle [%] = (1 - Vp3/Vp6) * 100
Example of a measurement with the warm engine running at idle speed:
- Vp6 = 14.1 V
- Vp3 = fluctuating (every second) between 6.9 V and 7.6 V
- Duty Cycle = fluctuating between (1 - 6.9/14.1)*100 = 51% and (1 - 7.6/14.1)*100 = 46%
Instead of doing ^this math, here is a handy alternative:
- print out the (blank version of the) attached diagram
- draw a line diagonally from your Vp6 (on the x-axis) to “100“ (on the y-axis)
- draw a vertical line from your Vp3 to your diagonal line
- draw a horizontal line from the intersection to the left and read the Duty Cycle in “%“
The attached example is done with the above measured Vp6 & Vp3.
H.D.
How to get duty cycle match at both idle and higher RPM? Would you comment on this?:
www.benzworld.org
EHA and fuel distributor lower chamber spring adjustments
Does anyone have a rule of thumb how much one turn or one degree on the lower chamber adjustment screw adds or substracts fuel on individual injector? As I was working on the distributor did some thinking. Many people have been found helpful to change EHA basic setting to get the system working...
www.benzworld.org
By making sure that, for instance:
- the injectors are properly working over the engine’s full speed range
- the FD’s metering slits are in proper condition (clean and not corroded)
- the FD’s control plunger & the air flow meter are smooth-running over the full range
- the FD is properly calibrated
- there is no vacuum leak that varies in size depending on the engine speed
- the o2 sensor is properly working over the engine’s full speed range
- . . .
In ^this thread you ask:Would you comment on this?:
EHA and fuel distributor lower chamber spring adjustments
Does anyone have a rule of thumb how much one turn or one degree on the lower chamber adjustment screw adds or substracts fuel on individual injector? As I was working on the distributor did some thinking. Many people have been found helpful to change EHA basic setting to get the system working...
“Does anyone have a rule of thumb how much one turn or one degree on the lower chamber adjustment screw adds or substracts fuel on individual injector?”
This ratio (‘volume flow change per degree’) is not constant. The further these adjustment screws are turned counterclockwise the smaller that ratio becomes.
These ‘differential pressure valve adjustment screws’ should only be touched for the purpose of proper FD calibration, btw ! … (See what I said about FD calibration in This Thread)
In my case duty cycle shows computer has to correct mixture by adding fuel at higher rpm. That excludes air leak as a cause in my opinion. Also economy gauge at idle is now all the way to left. No corrosion or deposits at slits and plunger etc. are moving freely. Car passes emissions any time and injectors are new. I did turn those differential pressure valve adjustment screws quarter turn out after a simple balance measurement between ports which looked really good to my surprise. It helped. Control pressure at idle was increased from 5.82 to 5.85 and difference in duty cycle between idle and high rpm was decreased. I believe there is somewhat linear ratio between turns on differential pressure valve adjustment screws and control pressure.
Of the things I mentioned in my last post, “proper FD calibration” is the most important !
My answer in my last post did not refer to the ratio between adjustment degree & control pressure. It referred to your first question in your thread … (“Does anyone have a rule of thumb how much one turn or one degree on the lower chamber adjustment screw adds or substracts fuel on individual injector?”).
With the EHA connected (and active Lambda control) before & after your ¼ ccw turn on the adjustment screws, the control pressure increase that you saw was normal. The ¼ ccw turn on the adjustment screws increased the fuel flow to the injectors - causing the o2 sensor to react with respective input to the ECU - causing the ECU to react with slightly lower EHA current - causing the control pressure to rise slightly - causing the fuel flow to the injectors to decrease back to what it was before … now resulting in a lower duty cycle, of course.
With the EHA disconnected before & after your ¼ ccw turn on the adjustment screws, you would not have seen a change in control pressure … and the fuel flow to the injectors would be higher now, of course.
BTW, please bear in mind that, as I mentioned earlier, I’d like to use this thread as a general tutorial about the KE-Jetronic Lambda control. I ask to start/use separate threads about individual cases/issues. … Your first question (regarding equal duty cycle at idle & higher RPMs) was a general question that suits to the topic of this thread. I commented on your thread “EHA and fuel distributor lower chamber spring adjustments” here in this thread in order to emphasize that “These ‘differential pressure valve adjustment screws’ should only be touched for the purpose of proper FD calibration” … because, if their changed setting results in a not properly calibrated FD, the Duty Cycle’s diagnostic information is falsified. ...
H.D.
If the other conditions you mentioned in post 75 then fuel distributor is not correctly calibrated then I suppose. Air leak would require more fuel at idle. To get even duty cycle at static conditions at different RPM without load this car needs either EHA tweaked or a change in differential pressure valve adjustments. Of course i could try checking the rubber boot on top of throttle plate...There kind of is a separate thread on this subject.
I do not know if you have checked every potential cause of the uneven duty cycle readings on this car. Mind that the list of potential causes in post #75 is not a complete list ! … Remember what I said in post #71:
“So the whole fuel combustion process determines the amount of residual oxygen in the exhaust gas … hence the o2 sensor voltage … hence the EHA current … hence the lower chamber fuel pressure … hence the Duty Cycle. …
^This should bring, Duty Cycle affecting, things to mind that even most professional mechanics are not aware of and that are practically always overlooked here at BenzWorld, including things that have nothing to do with the fuel injection system.
“In that post I also said:
”… my main objective with this Lambda control thread is to convince readers
- to check the Duty Cycle more often
- and to touch the Lambda (as well as the EHA) adjustment screw way less often (if at all !) …”
I don’t say it is the case in your case, but a crack in that boot is often a “vacuum leak that varies in size depending on the engine speed” (as mentioned in post #75).
Please bear in mind not to go deeper into your car’s individual issue(s) in this tutorial thread.
H.D.
BTW, I frequently see Duty Cycle readings of (close to) 30% with ’ignition on / engine not running’ (instead of the specified 70% for non-California cars) leading to the assumption that the meter refers to the on/off signal’s ON-time … and that it just needs to be subtracted from 100% in order to get to the, according to MB’s definition, correct 70% reading (referring to the OFF-time).
But that is not necessarily correct ! .. The meter may be the right version and the 30% reading may be an error code, indicating a CTS (Coolant Temperature Sensor) related problem.
So, in order to play it safe, better use a voltmeter … and convert the readings into Duty Cycle (as described in post #72) ! … That way you always get to the correct Duty Cycle according to MB’s (unusual, however not ill-considered
) definition.H.D.
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