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1986 560SEL
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Discussion Starter #21 (Edited)
H.D.,
I had a chance to investigate the O2 sensor info. I referred to several of your other posts to piece together what I think is the way to test. These threads helped me:
https://www.benzworld.org/threads/99-9-duty-cycle.3004583/page-6 (particularly post #106 and up).
https://www.benzworld.org/threads/m103-rough-idle-and-vacuum-leak.2452785/ (particularly post #17 and all of page 2)

Findings:
1. black to battery ground, red to connected O2 sensor wires
  • Engine off, key on, - 453mV
  • Engine on, cold - 439mV. As the engine warmed up, readings slowly rose to about 898-904mV.
  • At idle, engine slightly running rough, around 700rpm. Idle then went to ~800rpm, then started fluctuating (slowly) 700-800rpm; Still measuring around 900mV.
Now At normal engine temp (80C),
- Idle (~1000rpm) at first steady around 830mV, then fluctuating 070-700, then steady again 830mV; this seemed to reoccur.
[email protected] 2500rpm, measurements were as follows: ~ 190-500mV fluctuating
- Back to idle (stayed at ~1000rpm now), fluctuating 090-700, then steady around 830mV.
Second go round:
  • @ 2500rpm, fluctuating, 150-680mV
  • Idle (1000rpm), 090-700mV
If I did quick throttle blips about 1/2 throttle or more, I got the same "stumble on initial power, and the readings were -002 to 175mV.
When I disconnected the O2 sensor wires, I had no stumble on full power blips, but the idle stayed around 1000rpm.

Measured with O2 sensor wires disconnected, measured at the female end from the O2 sensor:
First time:
  • @ idle - 900 static
  • @2500 - 880 static
  • @ idle - 900 static
Second time:
  • @ idle 896 static
  • @2500 884 static
  • @ idle - 899 static
Now O2 sensor wires still disconnected, , engine off , and measuring resistance, black still using battery ground:
-From the O2 sensor female wire connected to Voltmeter red wire - Resistance = 1.
- From the O2 wire opposite (I assume leading to the ECU) Resistance = 117.4 (I don't know if this is a correct measurement??)
From what I read, these were both supposed to be "0", or infinite??

Next I did warm engine on, idle still staying around 1000rpm, and measured AFM movement:
pushing plate down (almost stalling) - 950mV
pulling plate up with a magnet (really not much upward movement beyond where it was) - 885mV

I have not measured resistance at the sensor body yet, it is a bit difficult for me to get under the car at the moment. If necessary, I will find a way to do that, let me know.
Does this point to a faulty O2 sensor?? Novice that I am :unsure:, It seems that with the O2 sensor disconnected from the ECU it isn't reading voltage like it should?
Thank you.
 

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I consider it the highest of all issues in maintaining these engines in good running order - and most ill informed.
So do I. … There‘s no gasoline injection system that you can find more misinformation & misconceptions about on the internet (not only in forums) than the KE-Jetronic.

Most DIY or garage mechanics over the years have gone straight for the Tower adjustment screw (lambda adjustment screw) always assuming it is an idle mixture adjustment screw that will sort out a problem with idle etc. They still have the perception this mechanical injection system is much akin to a carby set-up.
Yep … and it‘s very difficult to convince them not to fiddle around with that adjustment screw, especially since often you can improve an engine‘s subjectively perceived running behavior that way. When they experience that they feel confirmed in their dealing with the system. They‘re not aware that they just mask the cause of the running problem that way … often with negative consequences for the engine. … And when you tell them that by fiddling around with that adjustment screw they wipe out the most valuable diagnostic information that the system provides, they look at you like they would if you‘d tell them that political offices are more and more held by descent, reliable and honest people. … LOL

I had a chance to investigate the O2 sensor info. ...
These are thoroughly performed o2 sensor voltage tests, Rand. (y)

However, the closed loop o2 sensor voltage tests (o2 sensor wires connected) are a lot more informative if accompanied at least by simultaneous EHA current tests, better also by simultaneous LCP tests. Such simultaneous closed loop tests give insight in the complete loop. They allow you to monitor what the o2 sensor tells the CIS-ECU, what the CIS-ECU tells the EHA, what that does to the LCP and whether the o2 sensor detects & reports the expected corresponding air/fuel mixture change to the CIS-ECU again.

Your separate closed loop o2 sensor voltage tests suggest that there‘s either a problem with the o2 sensor or with the CIS-ECU. A problem with the o2 sensor‘s connection to ground via exhaust pipe they don‘t excluded either. They do exclude a short between o2 sensor signal wire & ground though. Of the three remaining suspects mentioned in post #11 the o2 sensor is still the most likely culprit.

Your open loop o2 sensor voltage test (o2 sensor wires disconnected) with the AFM plate pulled up corroborate my suspicion that the Lambda adjustment screw has been messed with too far in clockwise direction. … How much play, if any, do you feel when you gently push the AFM plate down when the engine is not running ? (See what I said about AFM play in This Thread)

Just to be on the safe side, the adjustment tower was touched after the hesitation/stumble started, right ?

I‘ll be quite busy on the weekend and next week so that replies may take a little patience.

Thanks for your appreciation, Gentlemen. :)
 

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Discussion Starter #23
Update: In a PM, H.D. suggested I go ahead and order/install a new O2 sensor, based so far on my findings, and the fact the O2 sensor to my knowledge, is the original one. He suggested, and I do agree, doing the simultaneous tests on the EHA, O2 and LCP is a fairly difficult process.

I am going to replace the O2 , do the duty cycle measurements again, and then see about correcting the lambda adjustment properly... I won't touch it until I get the go ahead from H.D.!! Yes, it was adjusted after the hesitation/stumble started. I can see that checking the AFM plate seemed to indicate the car is running rich, and I don't know if that lambda screw was messed with before I got the car. Time will tell. I will post here again after the next phase.

Thanks all for reading and reflecting. Special thanks of course to H.D., who continues to further our education.
 

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H.D. suggested I go ahead and order/install a new O2 sensor, based so far on my findings, and the fact the O2 sensor to my knowledge, is the original one. He suggested, and I do agree, doing the simultaneous tests on the EHA, O2 and LCP is a fairly difficult process.
Right. … Doing these simultaneous tests is not too difficult either, but a little more difficult than doing the tests separately ... and you need more meters, of course. You put a voltmeter for the o2 sensor voltage, an amperemeter for the EHA current and a fuel pressure gauge and best also a duty cycle meter, best all analog, next to each other so that you can monitor them simultaneously while you do or let someone else do several tests. A video of the meters during the testing fascilitates the procedure significantly. You can rewatch it and pause it at certain moments so that you can monitor the interactions of the involved components in more detail. … Such simultaneous tests can be very revealing.

I am going to replace the O2 , do the duty cycle measurements again, and then see about correcting the lambda adjustment properly...
With the new o2 sensor installed I suggest, for a start, to check the play of the AFM plate at its zero position and to recheck the duty cycle. Proper duty cycle “adjustment“ should be done last at a later time.
 

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Discussion Starter #25
Is it correct that there is only one O2 sensor in this W126? A mechanic friend said he thought there were 4 (2 upstream, 2 downstream each side)? I have found no evidence of more than one.
 

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Discussion Starter #27
OK, I got my O2 sensor today, and installed it with no issues. I took the car for a test drive, and although symptoms were somewhat different, there are still issues.
  • On slow take off (normal traffic), there is an almost imperceptible hesitation for a second or two, then it goes away (improved from before).
  • 1/2 throttle from full stop, there is a bit more hesitation, and a very slight stumble (not always), then it goes well (improved from before).
  • 3/4 throttle from full stop, there is a few seconds of stumble, then it takes off.
  • full throttle from full stop, a big stumble, very quick ( and once or twice during testing I had a bit of a 'carb' backfire), then it really takes off.
  • giving it gas while already moving is fine now; no symptoms with a slowly increased pedal, or quick full pedal.
My duty cycle measurements are now as follows :
Key off: ......................................................................Duty cycle:
  • Vp6 (#2 & #6) - 12.76
  • Engine off, key on: 3.58.........................71.94%
  • plate deflection: 10.68............................16.30%
  • full throttle: 9.50......................................25.54%
Engine running:....................................................................Duty Cycle:
  • idle (still around 900rpm): 13.58-13.62.................3.13%
  • 2500rpm: 9.07-10.14..........................................31.55%
  • idle (~900rpm): 9.76-11.15 , (BUT: this returned after a minute or so to 13.57-13.58 and remained stable so I used this as my measurement)..............................3.27%
  • Vp6 now measured again, engine idle: 14.04
I did not yet measure new O2 sensor voltage or resistance, waiting to see if that's necessary.
I did check movement of the CFM plate, and I found it moved freely the first 1-2 mm, then it moved fully but with some resistance. Once fully down I let go and it came up smoothly and quickly. I retested (after priming fuel pumps), and it moved down with some resistance and came up nicely as I allowed a steady upward movement.

synopsis: symptoms are different, still present, though improved. Should my next step be to adjust the Lambda screw? Is it possible that because it is running somewhat rich
(found last time with the measurements made previously), these symptoms are related to that?

Thank you!
 

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I did not yet measure new O2 sensor voltage or resistance, waiting to see if that's necessary.
I did check movement of the CFM plate, and I found it moved freely the first 1-2 mm, then it moved fully but with some resistance. Once fully down I let go and it came up smoothly and quickly. I retested (after priming fuel pumps), and it moved down with some resistance and came up nicely as I allowed a steady upward movement.
Does the AFM plate (with the engine off !) sit at its correct “zero position“ ... with its top edge at the same hight as the top edge of the short cylindrical part of the air funnel (measured below the stop bracket), or maximum 0.2 mm higher ? … And does the AFM plate sit concentrically to the air funnel in that position ?

Furthermore, as ‘step 1‘ in post 3, I suggested to check the “movability of the AFM & CP (Control Piston)“. Did you also feel the CP following the AFM plate when you let it slowly move back to its zero position ? … You can check/feel that with your finger if you let it tremble a little during the slow upward movement of the AFM plate. You should feel the CP “dance“ on the roller at the other end of the AFM lever.

I suggest to check ^these things independently of the still existing symptoms. They, along with other things, should be checked before the final duty cycle readjustment via adjustment screw anyway.

Should my next step be to adjust the Lambda screw?
Yes … in the manner suggested in post 3 (‘step 2‘), namely by turning the Lambda adjustment screw about ¼ quarter turn (!) counterclockwise. As mentioned in that post, “mind what I said about turning the adjustment screw under “Adjustment procedures“ in post #2 of my Lambda Control Thread !, referring to the pushing down of the adjustment pin and its latching into the adjustment screw. ... Do this provisional adjustment with air filter installed & warm engine running at idle & voltmeter connected and see how much it lowers the voltage, respectively how much it raises the duty cycle at idle and at 2500 rpm … and what it does to the symptoms during driving.

Is it possible that because it is running somewhat rich (found last time with the measurements made previously), these symptoms are related to that?
Yes … as I said in post #16, with your Lambda adjustment screw having been messed with, an o2 sensor related problem is not the only possible problem. ;)
 

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Discussion Starter #29
After reading through post #28, I was pretty confused. Then I dug in and reread all the previous material I had already read (but didn't comprehend well). Eureka! I started to grasp the whole picture! Now I get it. By adjusting the pin as per your instructions (in the Lambda Control Thread), the voltage should lower, thus bringing the duty cycle measurements in conditions #4, #5 and #6 closer to the 50% duty cycle target. Small adjustments ccw to lean it out a bit, read the voltages, get as close as I can to 50% then road test.
I can see now, since reading over the initial measurements I made, then the new measurements after having installed a new O2 sensor, where the voltage figures and duty cycle %'s were off, and what I should get to by adjusting the pin.

I will recheck the AFM but it looked like it was seated properly and at the right height. My one question on this procedure is how do I "feel" the CP moving? I get that the CP works in conjunction with the AFM, adjusting the so called "lambda adjustment screw" changes the AFM position and thus the air/fuel mixture. But I am still a little 'foggy' as to where the CP physically resides... is it in the control tower, and is that what I am pushing on when I adjust the pin?? If so, how do I "feel" it move when moving the AFM plate?

Thanks again for all of this. It has taken time for me to start to understand the system, which for me is important. You did say that doing the testing is easy once you do it hands on, and thats what I found, as you said I would! But understanding what and why, thats a different story, and it is all making more sense to me now.
 

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By adjusting the pin as per your instructions (in the Lambda Control Thread), the voltage should lower, thus bringing the duty cycle measurements in conditions #4, #5 and #6 closer to the 50% duty cycle target. Small adjustments ccw to lean it out a bit, read the voltages, get as close as I can to 50% then road test.
I can see now, since reading over the initial measurements I made, then the new measurements after having installed a new O2 sensor, where the voltage figures and duty cycle %'s were off, and what I should get to by adjusting the pin.
If you want the duty cycle to be a provider of reliable full-value diagnostic information again, a number of other things have to be done before the final adjustment of the duty cycle close to 50% … all of which would not be necessary, if the adjustment would not have been improperly messed about with.

I had a little time today to make a simple schematic drawing for a better understanding.

Steuerkolben-Einstellung.JPG


For now (after the adjustment has been messed about with) turn the adjustment screw (2) via the spring loaded adjustment pin (3) in the adjustment tower (4) only about ¼ turn ccw and check what that does to the duty cycle in conditions #4, #5 and #6 and to the car‘s running behavior.

I get that the CP works in conjunction with the AFM, adjusting the so called "lambda adjustment screw" changes the AFM position and thus the air/fuel mixture.
It is not the AFM‘s position that is changed that way. It is the CP‘s position in relation to the AFM plate‘s position that is changed that way, as I tried to illustrate in the above drawing. … But the actual challenge (also for the vast majority of professional garage mechanics ;)) lies in the understanding that on the KE-Jetronic the air/fuel mixture is not changed by changing that position, unless the adjustment screw is turned cw beyond the point where the duty cycle reaches ~0% or ccw beyond the point where the duty cycle reaches ~100%, or Lambda control is not active ! … I explained that in detail in post #1 in This Thread.

But I am still a little 'foggy' as to where the CP physically resides... is it in the control tower, and is that what I am pushing on when I adjust the pin?? If so, how do I "feel" it move when moving the AFM plate?
The CP is part (1) in the drawing. It moves up & down in a precise sliding fit in the center of the fuel distributor. A compression spring & fuel pressure pushes it down; intake air pushes it up (via the AFM lever). … (Mind that the illustration of the FD‘s inside around the CP in the above drawing is a very simplified one).

In order to “feel“ whether the CP is following the roller at the other end of the AFM lever, first prime the fuel pumps via ignition key at least once. Then push the plate swiftly all the way down with your finger and let it slowly move back. Let your finger tremble a little up & down during the plate‘s complete upward movement. Then you should feel the CP “dance“ on the AFM roller.

Thanks again for all of this. It has taken time for me to start to understand the system, which for me is important.
You‘re welcome! … And take it one step at a time. Its design is considerably more sophisticated than commonly assumed. Not only the frequent suggestions to fix problems by turning the above adjustment screw are evidence of that. … ;)

H.D.
 

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Discussion Starter #31
H.D., thanks so much for the drawing and info in the last post, very helpful indeed!

All,
Following H.D.’s incredible instructions, and educating me in the location of the Control Piston (C.P), and it’s relationship with the AFM as well as how to test it for proper motion, I went ahead and found the AFM moved nicely as anticipated. Feeling for the CP movement was difficult to ascertain, but I was fairly certain the CP was in contact with the roller and thus moving with the AFM plate to what I felt would be considered normal.

Warning! – This is a rather long post, with lots of measurements! It was surprising to me how much I was able to ‘see’ measuring the voltages as the car ran, and knowing what they meant. This is really all so foreign to me, but like learning a new language, it starts to make more sense as you go through the process. Thanks to H.D. for the great education!

Next, I set up to adjust the Lambda control adjustment screw. First I took initial measurements again( to ascertain a true starting point), of the voltages when doing steps #4, 5 and 6 while measuring Pins 2 and 3 of the X11 coupling. My results follow: ( Note: at idle Vp6 measured 14.00mV )

4 – 13.44-13.45mV ; Duty Cycle: 3.9% ; idle 900 steady
5 – 9.15-10.08mV ; DC: 31.28% ; idle 2500
6 – 13.50-13.52mV ; DC: 3.5% ; idle 900 steady

I then adjusted the screw using the 3mm Allen wrench…. or at least I THOUGHT I did, but the new measurements didn’t change significantly. I then used the 3mm allen wrench and tried measuring again, but my measurements were still about the same. I found I needed to push down further, and when I did I felt contact. Then as instructed, I wiggled the allen key a bit and felt it make contact with the adjustment screw. Turning the screw, it was tighter than expected, and I was afraid of turning it too much, so the adjustment was minimal. Again I took new measurements and still not much difference.

The next time I turned it about ¼ turn and now I noticed a difference with my readings as follows:
4 – 8.70-9.70mV ; DC: 34.28% ; idle ~850, slight consistent surge, 10-20 rpm
5 – 7.25-8.10mV ; DC: 45.17% ; idle 2500
6 – 8.20-9.30mV ; DC: 37.50% ; idle ~850, slight surge as above

I then went for a road test, and I continued to have mild hesitation (but less) at ½, ¾ and full throttle. I had no hesitation accelerating as in normal traffic, from a stop.
Once back, I again adjusted the screw a bit more ccw (slightly less than ¼ turn) and took measurements:
4 – 6.92-8.13mV ; DC: 46.25% ; idle ~800, slight surge
5 – 6.05-6.86mV ; DC: 53.82% ; idle 2500
6 – 6.92-8.05mV ; DC: 46.53% ; idle ~800, slight surge

I then went for a road test and measured again after I got home:
4 – 6.82-8.03mV ; DC: 46.96% ; idle ~800, slight surge
5 – 6.08-6.85mV ; DC: 53.82% ; idle 2500
6 – 6.89-8.03mV ; DC: 46.71% ; idle ~800, still slight surge
I now had a very slight hesitation on ½, ¾ and full throttle, improved from the previous tests.

Once again I adjusted the screw very slightly but this time clock wise, watching my voltmeter until I saw it hovering around 6.91mV for a bit, then fluctuating 6.90-7.70, then returning and hovering again around 6.91mV (in previous posts, this was pretty close to what I believe I read was considered ‘normal’, around 7mV). Measurements were now as follows:
4 – 6.91-7.74mV ; DC: 47.67% ; idle ~800, fairly steady
5 – 5.50-6.70mV ; DC: 56.42% ; idle 2500
6 – 6.90-7.74mV ; DC: 47.67% ; idle ~800, fairly steady.
*I think these findings are still not right. This is a 1986 SEL with the M117 engine, and thus (according to H.D.’s explanations) the mean value at idle should be 5-15% higher than the mean value at 2500rpm.
However, I went for a road test, and NO hesitation or stumble on any of the accelerations as previously tested. Full stop and normal acceleration using ¼, ½, ¾ and full throttle.
The only issue remains a ‘slightly’ high idle at around 800rpm. There is a very minimal surge, likely ~10rpm. I hear it rather than see the needle move much. Otherwise, it is now running and accelerating beautifully.

Because the mean value duty cycle is inverse from what is expected (see [*] above), I assume there is more here that needs attention even though the car is now running significantly better and the duty cycle %’s are closer to where they should be. I will await further suggestions from H.D.!

I can’t express my gratitude enough for all the help the members here have provided, for this and other issues I’ve been able to tackle.
Particular gratitude and thanks to H.D., who explained the CIS-ECU system so well that even a pure novice like myself was able to do the work. Not only has it been gratifying but it's also been really fun. I love the fact that I now have a rudimentary understanding of the way the system works.
 

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Discussion Starter #32
I went for another road test today. I found that there is still a bit of a stumble when accelerating with almost full, to full throttle. It lasts from 1/2 second to 1 second then the car accelerates full out. The idle remains high in park/neutral, about 850-900rpm, and there is still a very slight surge, perhaps 10-20rpm.
I wonder if I should go back and try adjusting the screw a bit more?
 

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You‘re welcome, Rand.

I then adjusted the screw using the 3mm Allen wrench…. or at least I THOUGHT I did, but the new measurements didn’t change significantly. I then used the 3mm allen wrench and tried measuring again, but my measurements were still about the same. I found I needed to push down further, and when I did I felt contact. Then as instructed, I wiggled the allen key a bit and felt it make contact with the adjustment screw.
;) … Now you know why I said (in posts 2 & 28): “Mind what I said about turning the adjustment screw under “Adjustment procedures“ in post #2 of my Lambda Control Thread !

BTW, the voltages you measured at the X11 coupling are “V“ (not “mV“).

In post #41 in your Initial Thread you reported (for the first time) a sudden higher idle speed. I suggest to first make sure that there are no vacuum leaks. That‘s also one of the possible causes of too high duty cycle at 2500rpm in relation to the duty cycle at idle and of the still existing slight stumble with almost full, to full throttle.

I assume there is more here that needs attention even though the car is now running significantly better and the duty cycle %’s are closer to where they should be. I will await further suggestions from H.D.!
Yes, if you want to put things right, there is more that needs attention. It might take some patience with my limited time in the coming days, though.

I wonder if I should go back and try adjusting the screw a bit more?
Mind what I said about final duty cycle adjustment in posts 28 & 30. … ;)

H.D.
 

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Discussion Starter #34
Since my last test drive, I started doing more research about why the idle may be high – in addition to possible vacuum leaks as H.D. suggested. I came across several threads that addressed other issues people had and what they did. There was a lot of talk about the ICV and modifying that. Well I just didn’t feel that I had zeroed in on the “sweet spot” for my duty cycle, but I was afraid to mess with it seeing as how the percentages seemed to be in close proximity to what was actually expected.

I watched 3 or 4 youtube videos about building a smoke machine to test vacuum, and that was going to be my next step. Also taking off the ICV and cleaning it (as per the threads I read). Many different scenarios went through my head, but in the end I decided that H.D.’s advice was spot on, so I decided to tackle the duty cycle again.

I won’t bore you with the multiple measurements I made this afternoon, as I tried tweaking the adjustment screw both cw and ccw, then measuring, driving, rinse and repeat. After getting discouraged, frustrated, mad and upset several times, I finally hit the sweet spot! During my trials, at times I had a high rpm, then lower with a surge (800, surging 10-20 rpm), and an uneven ‘burbling’ exhaust noise, then up and down, with weird noises and surges. Watching my voltmeter as I continued to adjust the screw, suddenly the rpm sounded good, no surging, no burbling. I checked and the rpm was at a solid 750rpm, no surging, no burbling.

Here are my final measurements:

Vp6(at idle): 14.04V
#4 – 5.95-6.80mV : DC: 54.53% ; idle 750, steady
#5 – 4.24-5.40mV ; DC: 65.62% ; 2500
#6 – 5.96-6.92mV ; DC: 54.06% ; idle 750, steady

Before I got too excited I went for a test drive. I had solid acceleration at all speeds, no hesitations, no stumbles, and it idled in park/neutral at 750rpm, steady, with a steady pleasing exhaust noise.

I’m not sure these numbers are as expected when the engine is running right. But it sure seems like it’s running right! I am beyond happy! My sincere thanks to all the help from everyone, and of course H.D. in particular. Your understanding of the CIS-ECU system, and your availability to those of us in need, goes above and beyond expectations. I have a much better understanding of the entire system and feel fairly confident in this end result.
 

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I won’t bore you with the multiple measurements I made this afternoon, as I tried tweaking the adjustment screw both cw and ccw, then measuring, driving, rinse and repeat. After getting discouraged, frustrated, mad and upset several times, I finally hit the sweet spot! During my trials, at times I had a high rpm, then lower with a surge (800, surging 10-20 rpm), and an uneven ‘burbling’ exhaust noise, then up and down, with weird noises and surges. Watching my voltmeter as I continued to adjust the screw, suddenly the rpm sounded good, no surging, no burbling. I checked and the rpm was at a solid 750rpm, no surging, no burbling.

Here are my final measurements:

Vp6(at idle): 14.04V
#4 – 5.95-6.80mV : DC: 54.53% ; idle 750, steady
#5 – 4.24-5.40mV ; DC: 65.62% ; 2500
#6 – 5.96-6.92mV ; DC: 54.06% ; idle 750, steady

Before I got too excited I went for a test drive. I had solid acceleration at all speeds, no hesitations, no stumbles, and it idled in park/neutral at 750rpm, steady, with a steady pleasing exhaust noise.

I’m not sure these numbers are as expected when the engine is running right. But it sure seems like it’s running right! I am beyond happy!
This puts me in a bit of a dilemma. … On the one hand I really don‘t want to spoil the party and on the other hand I'd like to avail myself of the opportunity to make readers aware that this is a typical example of what often happens. … CIS-E cars often make people “discouraged, frustrated, mad and upset“ and tempt them to change the system's setting via adjustment screw. And if a “sweet spot“ that seems to “fix the problem“ is found, everybody is happy & excited… well, except this H.D. guy … LOL … which has to do with the fact that the problem is usually not really fixed that way. ;)

In post #39 in my Lambda Control Thread I said:
Most duty cycle readjustments that are done, even if they bring subjective improvement about, only mask the deviation’s actual cause(s) which continue(s) to exist, with negative effects !

With your engine‘s improved running behavior after the adjustment to the current range, it is definitely masking still existing problems … and its duty cycle is still only a meager provider of diagnostic information. ... In post #5 here in your thread I said that I recommended (in post #3) to turn the adjustment screw ccw because I wanted to give you a “temporary sense of achievement“, remember !? … ;)

You said that, after you bought this car, the first time that the adjustment screw had been tampered with was after the ‘stumbling/hesitation‘ began. With a probability bordering on certainty it was also tampered with in order to “fix“ a problem before you bought the car. When that was done, a “sweet spot“ was found too … which also made the car run acceptably well again, but already masked a problem/problems that obviously still exists/exist. And now, after the o2 sensor replacement, you practically did exactly the same.

Luckily, your mechanic friend had not turned the adjustment screw too far so that your initial duty cycle readings were still informative enough for me to cast doubt on the logic of the ECU‘s obvious constant attempt to make the a/f mixture leaner. These readings called for the test drives I recommended with disconnected EHA / o2 sensor, which clearly showed that these doubts were justified and that there was an o2 sensor related problem. Without this remaining information that the duty cycle still provided, it would certainly have taken more time to find out about that.

As I said before, in order to ensure that there are no further hidden problems and to recover the duty cycle as a reliable full-value provider of diagnostic information, a number of things would still have to be checked and, if necessary, fixed before the duty cycle is finally readjusted to a value slightly below 50% at idle speed. … These two things (no hidden problems & reliable diagnostic information), along with a number of other CIS-E related things, I have been trying to make CIS-E car owners aware of here at Benzworld for about 3 years. I have strong doubts about my success, though. … ;)

But don‘t feel urged now to tackle these things. Currently I‘m too busy with other things for detailed respective assistance, anyway. For those who are familiar with CIS-E engines it‘s not difficult, it just takes some time. But it is rather challenging for those who are not very familiar with the KE-Jetronic. … And your car is certainly not the only one. By far most CIS-E cars that are still on the road and run well (according to subjective perception) do not provide full diagnostic information via duty cycle due to improperly changed Lambda adjustment screw setting (and EHA adjustment screw setting) and have problems that are hidden by such improperly changed settings, partly with more or less life-shortening consequences for the engine.

For detailed explanations why “fixing“ problems by simply changing the setting of the Lambda adjustment screw is not advisable, I recommend a close look at my Lambda Control Thread.

Good weekend everybody! … :)

H.D.
 

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1986 560SEL
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Discussion Starter #37
H.D., please do NOT feel like YOU are in a dilemma! I am very pleased about how the engine is running, but I knew that the settings were still not right based on your previous postings. Your continued sage advice is extremely important to me (and I am sure to everyone else that not only reads this thread, but the many others you have posted on this forum). I certainly want to get to the bottom of this - in fact I look forward to being in 'Sherlock Holmes' mode, and continuing the investigation, and hopefully the fix(es), to set this straight!
I will not stop following your recommendations... you obviously are the master of this system, and I am a neophyte!

Yes, I like the way it is running now, but I would not hesitate to continue exploring why the numbers are not right even though it is running right. It's sort of like a guy who may have a bad heart and has no symptoms. Eventually it comes to a bad ending! I want to be pro active and fix the problem, not cover it up.

I will enjoy the car as it is currently but I will look forward to further comments and suggestions you have to educate me further and get my car set up correctly. I express my continued thanks and grateful appreciation
 

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Outstanding Contributor
1988 300CE
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Yes, I like the way it is running now, but I would not hesitate to continue exploring why the numbers are not right even though it is running right. It's sort of like a guy who may have a bad heart and has no symptoms. Eventually it comes to a bad ending!
Right … turning the adjustment screw to a “sweet spot“ may stop symptoms but not the cause of the symptoms.

And the analogy you mentioned might be more suitable in this case than you may think. … In your (car‘s) case the cause of the symptoms might be a problem with the FD … the ‘heart‘ of the KE-Jetronic. There could, for instance, be ‘arteriosclerosis‘ in the upper part of (some of) the metering slits. That can happen if, for instance, the car sits a lot with a high content of ethanol in the fuel system … similar to what happens to us if we sit a lot with a high content of cholesterol in our cardiovascular system. :giggle:

BTW, especially if the car sits a lot, it is advisable to use a good additive in case of fuel with high ethanol percentage. It counteracts the harmful effect of ethanol … much like omega-3 fatty acid counteracts the harmful effect of cholesterol. ;)

As I explained in my Lambda Control Thread, the duty cycle adjustment is actually an EHA current adjustment which determines the EHA‘s opening degree during Lambda control. When the adjustment screw is turned ccw, the CP (part #1 in the drawing) is set to a lower position in relation to the AFM plate and in relation to the (vertical) metering slits (#5 in the drawing), thus reducing the opening cross section of the metering slits. The ECU immediately reacts (due to input from the o2 sensor) by sending stronger current through the EHA in positive direction, reducing the EHA‘s opening degree too, thus compensating for the reduced opening cross section of the metering slits. That way the symptoms of the (partly) clogged upper part of the metering slits may be stifled … however, with the consequence that the engine runs too lean whenever Lambda control is not active !

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If you wonder how a reduced opening cross section of the metering slits is compensated by a reduced (instead of increased) opening degree of the EHA, see what I said in post #66 in your Initial Thread. … Maybe I should amplify ^this drawing a little (when I have time) for better understanding of this hardly known, but for proper troubleshooting important to know, functionality.

I want to be pro active and fix the problem, not cover it up.
I will enjoy the car as it is currently but I will look forward to further comments and suggestions you have to educate me further and get my car set up correctly.
(y) … As I said before, in order to ensure that there are no further hidden problems and to recover the duty cycle as a reliable full-value provider of (troubleshooting time reducing) diagnostic information, a number of things, or better, everything that has an effect on fuel combustion) has to be checked, if the Lambda adjustment screw (or the EHA adjustment screw) has been unprofessionally tampered with … which on your car is obviously the case, like on most CIS-E cars out there.

I generally recommend to do that after purchasing a CIS-E car, especially if the anti-tamper plug in the adjustment tower is missing. … ;)

H.D.
 

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87 Euro500HVSEC. 88 Euro 560HVSEC. 89 Euro 560HVSEL
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4,215 Posts
With a 30yr old FD there is more than a 50% chance that it is not in spec (tiny splits in diapghram - deteriorated o-rings causing blockages in very fine capillary tubes etc etc) and i suppose before jumping into a rebuild i feel the DIY home test with the vials/glass jars to accurately measure flow from each injector line is a good start

The other main issue is a vacuum leak somewhere and requires a smoke test before you do anything else with the tune-up

And most important Injectors that are not spraying an even fine mist when they open (even new injectors requre bench testing before are swapped in) and injector seals that have gone hard with age and not 100% sealing.
I was not the least surpised when testing some of my injectors i have pulled and bench tested in the past - that they were not up to spec and spraying correctly

Doing a test on the POT upfront i would also consider essential (an easy test to perform) to eliminate any worn tracks as an issue.

Just my two bobs worth before any tuning process is commenced
 

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Outstanding Contributor
1988 300CE
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Just my two bobs worth before any tuning process is commenced
Right … along with other things that can all be checked / tested … which would not be necessary, or at least advisable, if the adjustment screw would not have been fiddled around with !

With the title of this thread being “Understanding Duty Cycle, and measurements“ I warmly recommend CIS-E car owners (again) to consider that everything that has an effect on the fuel combustion has an effect on the duty cycle, not only fuel system related things. If the Lambda adjustment screw (and/or the EHA adjustment screw !) has not been fiddled around with and the duty cycle is regularly (at least when new symptoms appear) checked, none of these things can go unnoticed. They all leave their traces on the duty cycle.

The duty cycle is one of the most valuable, yet most ignored, diagnostic tools on CIS-E cars. If CIS-E car owners would be more aware of that, this tool would a lot less often be destroyed by unprofessional & careless dealing with these adjustment screws … and a lot less time & money would be wasted on troubleshooting.

As I said before, the difficult to remove anti-tamper ball in the adjustment tower is a lot more justified than people imagine. That ball may have been removed on most CIS-E cars out there, but not its purpose. … ;)
 
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