Mercedes-Benz Forum banner

1 - 20 of 60 Posts

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #1
I have been having a discussion regarding my 560SEL, high idle, and a 'hesitation/stumble" at certain times. This discussion (about 5 pages) is in this thread:
https://www.benzworld.org/threads/questions-i-queried-the-forum-about-but-not-enough-info.3036076/
Which contains an incredible amount of excellent information and advice about the KE-Jetronics constant (fuel) injection system (CIS) from helpful forum members, most especially "H.D.". If you search his posts, it is amazing how much information he has given to this forum over the years. But you have to do the search. And you MUST be willing to invest some time to really understand. I am starting to get it after several weeks of trying.

This thread is a continuation of the one referenced above. I decided to start a new thread so I could have a title which matches what the discussion is about, making it easier to find this thread. I am still dependent on input from the folks here, so I can understand (maybe?!?) the significance of the measurements I have taken. Please read that thread to have a grasp on what this thread is about.

Synopsis: my '86 560SEL developed a hesitation/stumble when accelerating from a stop, or picking up speed in a normal traffic flow. At the same time the idle went from normal (~700) to high (~1000). No apparent reason for any of this.

Current symptoms (after 3 tanks of gas with "Sea Foam", new plugs, wires, rotor, condenser, and replacing a leaking ECV, checking all injectors, cleaning 2 that are now fine ) .....
1. on normal acceleration from a stop : a very, very slight 'hesitation' (this is much less pronounced than when I started) ; on acceleration from a stop with 1/2 to 3/4 throttle : a more pronounced 'stumble' for a second or two, then accelerates strongly ; on full throttle acceleration from a stop : bogs down for a second or two , with an occasional intermittent "backfire" from the air deflector plate (I assume thats where its coming from as it is under the hood) ; slight hesitation/a bit of a stumble, when in a normal traffic flow and accelerating to keep up with traffic.
2. Idle is still high after warm up, but better. It was running 1,000 - 1,100, now it seems to have settled in around 900. Cold start, the idle is fine, around 700.

I took Duty Cycle measurements today for the first time, after spending a lot of time trying to figure out how it is done. With a very patient member H.D., and others, I was able to this, and now I realize that the act of taking the measurements is much simpler then it seems. If I can do it, anyone can!

What I don't quite get yet is the significance of these readings. I am posting them here and will await word on what to do next.

#1 - measured at coupling X11, #2 port (black lead) and #6 port (red lead), engine off, key off : 12.6V [Vp6] ( port #2 = ground ; port #6 = battery )
#2 - measured at coupling X11, #2 port (black) and #3 port (red), for the next 6 conditions: [Vp3] ( port #2 = ground ; port #3 = what's being tested)
a. Engine OFF (cold), key ON - 3.68V
b. Engine OFF, (cold) Key ON, air sensor plate deflected ~ 1/2 way : 10.89V
c. Engine OFF, (cold) Key ON, full throttle (air deflector normal) : 9.71V
d. Idle speed (engine warm) : 13.51-13.53V
e. at ~ 2500RPM : 9.4 - 40.7V
f. idle speed : 13.56-13.57V
Lastly, tested at idle for Vp6(battery) between port 6 and port 2 = 14.00V

According to the duty cycle voltage conversion formula [ 1 - (Vp3/Vp6)] * 100 = Duty Cycle :
ENGINE OFF
a. key on : [ (1 - (3.68V/14.0)*100] = 73.71%
2. air plate deflected : [ (1-10.89/14.00)*100] = 22.21%
3. throttle full, air deflector closed : [ 1 - (9.71/14.00)*100] = 30.64%
ENGINE ON, WARM
4. idle speed : 13.51 - 13.53V [ 1 - (13.51/14.00)*100] = 3.5%
[ 1 - (13.53/14.00)*100] = 3.3% MEAN : 3.40%

5. 2500rpm : 9.4 - 10.7V [ 1 - ( 9.4/14.00)*100] = 32.8%
[ 1 - (10.7/14.00)*100] = 23.5% MEAN : 28.15%

6. idle speed : 13.56 - 13.57V [ 1 - (13.56/14.00)*100] = 3.14%
[ 1 - (13.57/14.00)*100] = 3.07% MEAN : 3.11%

NOTE : my tower Lambda adjustment screw HAS been adjusted previously.


OK, that's been completed. It was indeed a LOT simpler then I thought it would be. Reading about how to do it, and actually doing it, are 2 different things. Now if those of you that are the "brain surgeons" of the CIS can help me understand what this tells me, and can perhaps help diagnosis the problem(s) I'd be forever grateful:D

 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
Thanks for your appreciation Randtor. :)

I took Duty Cycle measurements today for the first time, after spending a lot of time trying to figure out how it is done. With a very patient member H.D., and others, I was able to this, and now I realize that the act of taking the measurements is much simpler then it seems. If I can do it, anyone can!
Haha … you see!

When DIYers or mechanics come to me with a CIS-E car asking me for advice regarding an engine issue, I usually ask them whether they have checked the ‘duty cycle‘ yet. If they say they have not because it seems to complicated for them, I sometimes ask my wife, who is not a mechanic and certainly does not look like one either, to come out and show them how to do it. Nothing motivates ‘car guys‘ to understand quicker how to do a duty cycle check than that. … LOL

I saw and still see many threads here at Benzworld with many unnecessary part replacements done/suggested which could be so easily prevented by a simple duty cycle check … which, if the engine is already warm, is done in less than 5 minutes (from opening the hood until closing it again).

You made only one small mistake in the ‘voltage to duty cycle‘ conversion. For all conversions you used the Vp6 reading that you took with the warm engine running. … But Vp3 at ignition on has to be divided by Vp6 at ignition on (in your case 12.6 V) … and Vp3 at warm engine running has to be divided by Vp6 at warm engine running (in your case 14.0 V). So your actual duty cycle values at ignition on (your measurements 1, 2 & 3) are slightly different from the ones you posted.

What I don't quite get yet is the significance of these readings. I am posting them here and will await word on what to do next.
As I emphasized in post #39 of my Lambda Control Thread, the “significance“ of duty cycle readings is generally not only way underestimated. What‘s even worse & counterproductive is looking at the duty cycle as something that simply needs to be readjusted via adjustment tower … let alone the fiddling around with that adjustment tower without even caring about the duty cycle.

Unfortunately, the latter has been done on your car. As explained in your Initial Thread, that destroyed most of the diagnostic information that the warm running engine‘s duty cycle (your measurements 4, 5 & 6) would otherwise have provided. Fortunately, however, in your case these measurements still do provide some useful information. At least several possible causes of the symptoms you described can now be excluded, and some become more likely.

Now disconnect the EHA plug when the engine is not completely cold (30-50°C). Then go on a test drive and see how the car behaves. The result should lead to further specific “word on what to do next“. ;)

H.D.
 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
One more thing Randtor. … When I said “go on a test drive and see how the car behaves“ (with the EHA plug disconnected) I should have mentioned that, with your duty cycle readings 4 & 6, it is possible that the engine can not be started then, which would also provide some helpful inside.

As I said, unfortunately, your Lambda adjustment screw has been messed with. In post #83 of your Initial Thread, I quoted the following from my Lambda Control Thread:

Tampering with the Lambda adjustment screw without even checking or caring about the duty cycle (or the EHA current) is an even worse idea than simply readjusting a deviated duty cycle without caring about what‘s causing the deviation … with even higher risks for the engine’s health !
Plus, done without at least knowing exactly how far in which direction the adjustment screw has been turned, valuable diagnostic information is gone for good (!) and everything that has an effect on fuel combustion (see examples under “Please note“ in post #2) has to be checked first before further touching the adjustment screw, in order to reliably restore a proper condition of the system.“


That‘s where you (and many other CIS-E car owners) are now. … The significance of the reason for the difficult to remove plug in the Lambda adjustment tower of the KE-Jetronic is way underestimated. Most DIYers & mechanics have no idea how much guessing and trying and time & money wasting can be prevented if the Lambda adjustment screw has either never been unprofessionally messed with or if it has been properly reset !

However, your duty cycle readings 1, 2 & 3 (the ones with only ‘ignition on‘) do show a few things:
The CIS-ECU is properly receiving supply voltage (via OVP). That missing is certainly not the only potential cause of the symptoms you reported, but one of the most typical causes, which can now be excluded in your case. That, however, does not show that your idle speed control ECU is properly receiving supply voltage too.
The CIS-ECU is also receiving proper input from the TPS (Throttle Position Switch).
And, with the AFM in its rest position, the CIS-ECU is receiving proper input from the AFM potentiometer, which does not prove that it is also doing that when the running engine is being accelerated.

What your duty cycle readings 4, 5 & 6 (the ones with the warm engine running), however, do suggest is to check the following things first:

1) Movability of the AFM & CP (Control Piston). I explained how to do that somewhere in This Thread.

2) Engine‘s running behavior after turning the Lambda adjustment screw counterclockwise. Start with maximum a quarter turn. If that improves the engine‘s running behavior, keep that adjustment for now. With the information what the duty cycle with the warm running engine is now you can do that free of risk. … Mind what I said about turning the adjustment screw under “Adjustment procedures“ in post #2 of my Lambda Control Thread !

3) Leak-tightness of the CSV (Cold Start Valve).

4) Fuel pressure (SP & LCP) with the EHA plug disconnected and the FRP (Fuel Pump Relay) jumpered (engine not running).

5) Spray pattern of all 8 injectors.

6) Electric resistance of both AFM potentiometer carbon tracks along the complete AFM plate‘s travel. The input track is checked between pins 3 & 1 and the output track is checked between pins 2 & 1. I talked about that somewhere in This Thread too.

I post this now, because up from tomorrow I‘ll be quite busy with other things and probably too short of time for it.

H.D.
 

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #4
H.D., thank you for all this information. Time consuming effort on your part and much appreciated on this end.
You made only one small mistake in the ‘voltage to duty cycle‘ conversion....
I am going to redo the math just so I can look at the difference, and also to learn how it's done properly. I'll review the instructions as I did not remember that part, thanks.
Now disconnect the EHA plug when the engine is not completely cold (30-50°C). Then go on a test drive and see how the car behaves.
I should have mentioned that, with your duty cycle readings 4 & 6, it is possible that the engine can not be started then
I will try disconnecting the plug and see if it starts. If it does, I will drive for a bit and see how it runs. If it doesn't start i will reconnect, start it up, then disconnect and see if it continues to run... if so, I'll take it for a ride (a short distance lol!)
and report findings.
I will also look up all of the info I can on your points #1 - #6, and follow your directions/suggestions.

H.D., Do I assume these steps #1-#6 should be performed in the order you listed?
Cheers!
 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
I am going to redo the math just so I can look at the difference, and also to learn how it's done properly.
(y) … What I‘ve said in posts 2 & 3 is based on the correct conversions of your voltage readings to duty cycle.

I will try disconnecting the plug and see if it starts. If it does, I will drive for a bit and see how it runs. If it doesn't start i will reconnect, start it up, then disconnect and see if it continues to run... if so, I'll take it for a ride (a short distance lol!) and report findings.
(y)

H.D., Do I assume these steps #1-#6 should be performed in the order you listed?
I recommend to do step #1 first. Step #2 is actually best done last. (I listed it as #2, because it might give you an earlier temporary sense of achievement :)). The order of the other steps doesn‘t really matter.

Cheers!
 

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #6 (Edited)
H.D., I just went out and did the very first suggestion, ie: warmed up the car (10 min ride), unplugged the EHA, and it started right up. I took it for a ride and it was a totally different car! It ran beautifully, none of the described symptoms... no stumbles, no hesitations in all driving modes. In park or in neutral, the idle went up to about 900 at first then settled right in at 700rpm. Full throttle from stop, 1/2 or 3/4 throttle, gentle throttle... all was perfect!
THAT was a great sense of accomplishment right there!!!
Now if you would be so kind as to tell me (briefly, I know you are pressed for time) what that means and what to do next, I'll refrain from any of the other steps until I hear from you.

Wow... I could hardly believe the instant correction of all faults just unplugging the EHA!

Edit: I just read through the links you provided in post #3 and will refer to them again should I need to proceed further with your list, after you have further instructions since I found such an improvement after unplugging the EHA.
Rand
 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
THAT was a great sense of accomplishment right there!!!

Wow... I could hardly believe the instant correction of all faults just unplugging the EHA!
Haha … it‘s a fundamental intention of mine to contribute to other people‘s joy, despite the fact that they (not only car people) often think I just want to torture them with tiring explanations. … LOL

Now, this is not the solution, of course. Doing a test drive with the EHA plug disconnected was just a logical first next diagnostic step that your duty cycle readings called for.

This might give you an idea of the value of a duty cycle check, especially if you consider that in your case the duty cycle is only partly reliable, because the Lambda adjustment screw has been messed with. Imagine how helpful a completely reliable duty cycle can be (if you understand what it‘s telling you, of course) … especially if you can monitor it anytime, for instance with a device like the one I introduced in This Thread. ;)

In your case steps #1-#6 still make sense.

What do you know about the o2 sensor, the CIS-ECU, the EHA and the FD in your car? … Are they the original parts or are they replacements? … In case of replacements, used or new? … Has the small adjustment screw on the back side of the EHA been touched?

I may not be able to post further replies tonight. My wife and I have friends over. 🍷

Cheers!
 

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #8
Haha … it‘s a fundamental intention of mine to contribute to other people‘s joy, despite the fact that they (not only car people) often think I just want to torture them with tiring explanations. … LOL
Well I for one... and apparently MANY others on the 126 forum... appreciate your "tiring" explanations! On the contrary, my brain is kept wide awake trying to grasp what you are saying! It takes a while, I am not well versed in electrical repair, but I do get a lot of it. I have been reading through the threads that you make reference to, and my oh my.... I think I need a degree in electrical engineering. BTW, I have been talking to my friend about your Duty Cycle monitoring unit, and he is going to get together with me and see if we can build it, or something equivilant. I'm excited at the possibility!

What do you know about the o2 sensor, the CIS-ECU, the EHA and the FD in your car? … Are they the original parts or are they replacements? … In case of replacements, used or new? … Has the small adjustment screw on the back side of the EHA been touched?
I did replace the EHA last week, we found it leaking (mentioned in my previous thread). We didn't do anything with an adjustment on the actual EHA. I only know of that from your mentioning of it in other threads. We checked the FD and found 2 injector pipes not weeping gas when the car was running and nuts were loosened, those were cleaned and both worked fine after that. AFAIK the O2 sensor and the CIS-ECU are original. When I purchased the car late last year it ran just fine, with minimal issues unrelated to the current problems., such as a non operative cruise control, outside temp readout, etc. All since fixed. The only items left on my "to do" list are passenger side mirror (only works horizontally, not vertically) and seat spring reinforcement on the 2 front seats. The PO had a lot of work done (I obtained a copy of several bills totaling over $6300 worth of work he had done professionally. A lot of front and rear suspension work, r/r cylinder heads, head gasket, timing chain, guides and tensioner; replaced intake seals, injector seals, rear engine crank seal, replaced engine mounts, repaired #8 spark plug hole).

I may not be able to post further replies tonight. My wife and I have friends over. 🍷
Habe einen wunderschönen Abend !!
I'll await further info and instruction at such time as you are able to post. I have been seeing more and more evidence of the hundreds of posts you have made relative to this system, it is an incredible amount of information. This forum is so very lucky to have someone with your knowledge willing to spend vast amounts of time helping us out.
 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
Okay, then reconnect the EHA (!) and to disconnect the o2 sensor connector under the carpet in the passenger footwell (single connector with green wire). Then start the cold engine and do a test drive long enough to see how the car behaves not only up from a cold start but also when it‘s at full operating temperature.

Thanks again for your appreciation, Rand. :)
 

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #10
Hi H.D., I was able to get some time to check this morning. I plugged the EHA back in, unplugged the green wire (O2 sensor connector) and started it up. It run a bit rough on cold start (I am fairly certain this was the same as when I had the EHA unplugged), but the idle came right down to ~ 700rpm. I went for a drive and tested everything the same way as before. From a dead stop, with 'city' acceleration, then 1/2 throttle, 2/3 throttle, and full throttle. No hesitation, stumbling or 'popping' from the engine bay! It drove and accelerated beautifully. Putting it into park or neutral, the idle went to about 1000rpm, then slowly seemed to settle into 700-750.
To be sure, I plugged the O2 wire back in, and continued my ride. Yes, the symptoms came back... hesitation/stumble/high idle. Again unplugging the wire, all symptoms cleared up. It ran like a thoroughbred race horse! When I drove into my garage and put it in park, the idle went up to 1000rpm. I sat there contemplating, and suddenly the idle dropped to around 750, then 700, ran a bit rough at these 2 points, and just as suddenly the idle went back up to 1000rpm. So I sat for a while, and the process continued.... 1000rpm, for 30-45 seconds, then dropping to 750, slight rough, 700 a bit more rough, then back to 1000, and smooth.

I will wait to hear your diagnosis :unsure:. I am curious if this means the O2 sensor is bad, not giving proper voltage and throwing off the system? I'm pretty sure you already know lol!

BTW, I redid my figures seeing as how I mistakenly used the same Vp6 measurements cold and running. Final Duty cycle numbers (engine off, key on) ended up as follows:
#1 - 70.79%
#2 - 13.57%
#3 - 22.93%

Thanks again,
Rand
 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
I will wait to hear your diagnosis :unsure:. I am curious if this means the O2 sensor is bad, not giving proper voltage and throwing off the system? I'm pretty sure you already know lol!
Hahaha ... looks like the culprit is caught in a trap it will not be able to escape from, doesn't it. ;)

It‘s either the 02 sensor, or (less likely) the CIS-ECU, or a short between the o2 sensor wire & ground, or a missing connection between the o2 sensor housing & ground (via exhaust pipe → engine → ground strap).

All these things can be tested, of course. Checking for a short between the o2 sensor wire & ground is the easiest. Checking for proper connection between the o2 sensor housing & ground is also very easy if you can reach the o2 sensor with the test prod under the car. Testing the o2 sensor and the CIS-ECU is also not difficult, but explaining how to do that takes more time than I have right now.

So I suggest to check for that short to ground & that connection to ground. If these things are okay, I suggest to replace the o2 sensor. To get it out of the threaded socket it sits in it may have to be heated with a blowtorch.

After that‘s solved check the duty cycle again. This time only the measurements with the warm engine running matter.

Don‘t worry about the idle behavior at this stage.

H.D.
 

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #12
Awesome H.D. !
I'm not really sure exactly how to test what everything you mentioned, but I will do a youtube or internet search if necessary, for more info on this. I understand your time is limited, and as always, much appreciated! You have such a wealth of knowledge with this system, I don't know how you have managed to answer all the threads that you have answered in the past!

If anyone else reading this thread can take some time to explain how to test these things, that would be helpful. As mentioned before, I am a novice with all this, and even tho I can turn wrenches, admittedly the electrical components in ANY vehicle always throw me! I've messed around with my 3 Triumphs and figured it out, so I am pretty sure I can do the same here.

I will do the checks and come back to report my findings, probably some time this week.

Thank you again! (sorry, I can't say it enough!)
Rand
 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
You‘re welcome, Rand. :)

If anyone else reading this thread can take some time to explain how to test these things, that would be helpful.
Most likely the o2 sensor itself is the culprit.

If you want to check for proper connection of the o2 sensor housing to ground, you might want to ask your friend to check resistence between a metallic bright spot on the o2 sensor housing & ground (or the battery minus pole).

To check if there‘s a short between the o2 sensor signal wire & ground, ask him to check resistence between the female part of the disconnected o2 sensor connector & ground and between the male part of the connector & ground.

If you want to know for sure whether it‘s the o2 sensor or the CIS-ECU, I explained a few tests in This Thread that would bring insight.

H.D.
 

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #14
H.D., as always, your input is appreciated, thank you! My mechanic friend left for Florida last week for the winter, but I can do this on my own based on your instructions. I will test this out this week and report back.

I am curious though, how you interpret the results of the duty cycle check. What pointed you in the direction of first unplugging the EHA, and then nailing the O2 sensor as the most likely culprit? I know explaining this procedure is likely going to be time consuming - and very possibly like trying to explain advanced aeronautical engineering to a grade schooler !! But perhaps you can point me to another thread you might have here that will educate me (us!) without having to write everything up again.
Best,
Rand
 

·
Registered
1986 560SEL
Joined
·
107 Posts
Discussion Starter #15
I have been searching the forum and, in addition to the link sent by H.D. in post #13, I have found several more helpful threads posted by H.D. on this subject. Thank you! I won't be able to check the O2 sensor for a couple of days but I will post my results here when done.
 

·
Outstanding Contributor
1988 300CE
Joined
·
1,424 Posts
I am curious though, how you interpret the results of the duty cycle check. What pointed you in the direction of first unplugging the EHA, and then nailing the O2 sensor as the most likely culprit? I know explaining this procedure is likely going to be time consuming - and very possibly like trying to explain advanced aeronautical engineering to a grade schooler !! But perhaps you can point me to another thread you might have here that will educate me (us!) without having to write everything up again.
That‘s a very good question. (y) … Unfortunately, due to limited time I can only give you a very superficial answer right now.

I was planing to explain in detail how to interpret the “duty cycle“ earlier this year, when I had more time. Since early March there had been technical forum problems that I preferred to see fixed before I post these things. But they were not fixed. Instead, the forum suffered a severe downgrade in August. And worst of all, several extensive posts of mine have completely disappeared from this forum since that downgrade. That‘s when my motivation to post these things here at Benzworld suffered severely. Since then I have only posted a few things in a few threads. This thread & your Initial Thread (which was already more than 40 posts and 6 weeks old when I stumbled over it) are the ones I posted the most in. Since no one had suggested a duty cycle check, which I generally suggest in case of engine running issues, I joint your thread and did that in my first post.

As I mentioned in that thread, with your Lambda adjustment screw having been messed with, your duty cycle readings were only partly reliable. But they did exclude some of the potential causes of the symptoms you described. They also showed that the CIS-ECU is continuously trying to make the air/fuel mixture leaner (via EHA control) … at idle speed even reaching the Lambda leaning limit.

So I wanted to see if that is a logical or an illogical attempt. Your test drive with the EHA disconnected suggested that it is an illogical attempt.

Then I wanted to see if a problem with the ECU or a problem with input to the ECU is prompting it to behave like this. With your Lambda adjustment screw having been messed with, a problem with the o2 sensor or its connection to the ECU or to ground or the processing of its signal by the ECU are not the only possible causes of that obviously illogical attempt. So I wanted to see how the engine behaves when only the o2 sensor is disconnected. Your test drive with it disconnected showed that at least one of these o2 sensor related things … most likely the o2 sensor itself … is the culprit.

H.D.
 

·
Premium Member
87 Euro500HVSEC. 88 Euro 560HVSEC. 89 Euro 560HVSEL
Joined
·
4,216 Posts
I hope those original post from HD can be retrieved by the mods.
The technical knowledge and info of the Bosch system that HD has contributed is so invaluable to so many owners across the globe.
I consider it the highest of all issues in maintaining these engines in good running order - and most ill informed.

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.
 
1 - 20 of 60 Posts
Top