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M103 Rough idle and vacuum leak

59K views 182 replies 14 participants last post by  KJZ78701 
#1 ·
My 89 300 SE with 262k miles has developed a rough idle. When warmed up it idles at around 550-600 rpm. The engine seems to be hunting as the idle will go very slightly up and down. Occasionally when coasting my engine will speed up and stay there for a few seconds before returning to normal speed. I need to depress the gas pedal to start the car, which I understand should be unnecessary. After starting, If I don't keep my foot in the gas for a few seconds the engine will usually die immediately but after restarting will usually stay running without depressing the gas pedal.

About 6 months ago I replaced the fuel filter and spark plugs due to the engine failing to start. Around 3 months ago I replaced the fuel pump relay due to the engine dying and failing to restart. I replaced the o2 sensor about 6 weeks ago after reading the check engine light codes.

I have tested the OVP, ICU, ICV, coolant temperature sensors, air flow sensor plate, throttle position sensor, and a variety of other components ( been working on it a while and I don't remember all I've tested) which have all tested to be working.

The economy gauge does not peg to the left (in the black) when warmed up and idling in drive with the AC off which I understand indicates a vaccuum leak. Using WD-40 I diagnosed a leak in an injector seal and replaced all 6 injector-to-housing seals. The car runs better now, but is not running perfectly. The economy guage still does not peg to the left, so I believe there is still a vacuum leak.

Before replacing the seals I would occasionally get a knocking sound in the engine while idling, but since replacing them about a week ago I have not heard it.

I suspect that the vacuum leak is not my only problem but likely is the largest problem. When testing for leaks I followed this wiki and did not find any other leaks. What are other locations in the vacuum that are likely to leak? I've searched the forum for a diagram but haven't found one for my chassis and engine, does anyone have a diagram?

Any information about a vacuum leak or other problems I have described will be greatly appreciated

Thank you,
Codycool55
 
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#3 ·
You need to go through and check ALL the vacuum lines and rubber connections (I need to do this with the Coupe' too), don't rule out the plastic hard lines as I had one or two of those that were leaking as well. Rubber can be replaced with proper sized line found locally. On my former SE there were several leaks found and fixed. How is the cap and rotor ?
 
#4 ·
I replied to your PM, but it looks as if good advice is already being provided.

It would help to click 'User CP' on the top toolbar and complete your profile with your car's year and mod (300SE or SEL) and at least a general location, like State if within US.
Daimler Benz made different versions of same model cars for different parts of the world, so to get the correct advice on a international forum, location can be quite important.
Mercedes Benz USA = MBUSA used to host these manuals free of charge for US resident members, unfortunately, that's no longer the case. Alternatively, as US resident, you can navigate to technical literature on MBUSA and see what is still available for your car.
 

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#7 ·
Teutones reply came at a great time! I actually just came back home from college for the summer and I'm looking to repair my car more. I was never able to replace the vacuum lines, and the rough idle never ceased. Lately I've been needing to replace the spark plugs excessively frequently (roughly every 6 months) as they are becoming fouled to the point where the car will not start. At times my engine would stall at a stop, if I accelerated too quickly from a stand still, and even when accelerating out of rolling corners. During the winter there were times the engine wouldn't start at all, and some of those times when I ceased cranking the engine the air flow meter plate would flutter and eject black smoke. These problems have went away since the weather has gotten warmer, but when coasting or stopped the idle is still low and feels as if it's dying and still a hard start. Once it's reved up to 1500 RPM plus it runs fine although it's lacking in power. Smells like its running very rich. I still plan to replace all the vacuum lines, but if these symptoms seem like something else let me know too!

Cody
 
#8 ·
You have a multitude of problems but I can safely say that your vacuum lines might not be the root cause of your problems.
So I guess i'm saying the symptoms seem like it is something else.

Have you determined if your Lambda system is working properly and taken some duty cycle measurements, especially when it smells like its running very rich? I suspect the air/fuel mixture is not being maintained/regulated in closed loop fashion.

What is the date code on your OVP? Check that please as a first step. You said you checked it for functionality, how did you do that?

You can also video your idle by recording your instrument cluster during these episodes of low idle, unstable idle. That may present us with a clue.
 
#9 ·
I figured it was more than just the vacuum lines.. But seeing as it's a 25 year old car couldn't hurt to switch out any rubber/ plastic parts I can get my hangs on

I checked the duty cycle at one point and it was acceptable, however I believe that was 2 years ago. I will check it again this weekend and get back to you!

The date code is 23/01/1998. Is this an expiration or a date of manufacture? Basically removed the OVP, started the engine, and noticed it was running much worse than with the OVP. Again, that was 2 years ago. Picture of date code.

Here's a video! This is stopped, in drive, with the AC off, warmed up after a few miles of driving. At about 20, 25, 30, and 35 seconds in (when the RPM dropped to nearly 0) I had to throttle up the engine as it was going to stall. At about 40 seconds (when the RPM moves up to around 700) in I shifted into park for the duration of the video.

I replied to your PM, but it looks as if good advice is already being provided.

It would help to click 'User CP' on the top toolbar and complete your profile with your car's year and mod (300SE or SEL) and at least a general location, like State if within US.
Daimler Benz made different versions of same model cars for different parts of the world, so to get the correct advice on a international forum, location can be quite important.
Mercedes Benz USA = MBUSA used to host these manuals free of charge for US resident members, unfortunately, that's no longer the case. Alternatively, as US resident, you can navigate to technical literature on MBUSA and see what is still available for your car.
I have updated my information!

I looked for technical literature on that site, but I think it only goes back to 2000 :( I (believe) I have found a download elsewhere though.
 
#10 ·
For some reason the links to your google photo album is not working for me.
But if your OVP is truly 19 years old, like you believe it is, it has to be changed. A KAE unit is about $45 I believe. Mercedes Benz brand might be slightly higher.
I would recommend KAE, that's what i used and was was in the car for 12 years.
I have tested 2 OVP's on my M103 in the last 2 months, one was 12 years old the other was 18 years old.
Both appear to be OK but both were having intermittent idle problems because the ECU kept switching on and off, most likely because of the internal relay circuitry being defective/worn in the OVP.

Whether the OVP is your main problem remains to be seen but it is quite likely. However I would like to see your idle first to see if it is similar to mine when I was having similar issues at a lesser extent.
Can you put it up on youtube instead and post a link?
 
#12 ·
I don't know how much help this will be and I'm doing it from memory here, the car was sold over two years ago. The 91 300SE I had for 12 years slowly over time got to running not as well as when I bought it. Over a period of trial and error I replaced all the rubber vacuum and two hard lines, got a duty cycle meter and adjusted the lamda/fuel mix, EHA was leaking a little and was replaced. It was about this point that sometimes I'd have to ride the shoulder uphill due to absolutely no power, downhill was better and this was erratic as hell. New cap, rotor, wires, and plugs (believe it or not 100K miles on the plugs that were in it when I bought it :eek I had read that aluminum heads sometimes had stripped plug holes, these didn't). She ran some better but still sometimes no power and when she did and I floored the gas it looked like diesel exhaust out the back. Around this point someone mentioned the cats may be plugged, I had a set of pipes made and dropped the cat, problem solved and she was still running quite well a year later when I sold her. The new owners are my neighbors in-laws and I still see the car from time to time
 
#13 ·
After seeing that video my money would be your OVP. It is similar to my '89 M103's behavior although not exact. You can try to measure the output of the OVP when the idle is cycling to see if it is cutting off at that exact time and coming back on.

But your OVP is so old it needs changing anyway, so you may as well just change it and see if your idle cycling issue goes away.

Your vacuum problem is separate in my opinion and should be tackled separately. I assume the AC was not running during the video.
 
#14 ·
Last night I checked my duty cycle by checking the voltage across pins 2 and 3 of the x11 using a multimeter. It read out a constant roughly 14.1 to 14.2 volts. So if my assumptions are correct this would indicate 0% duty cycle, meaning the system isn't attempting to adjust the mixture at all. Does that sound right?
 
#15 ·
... So if my assumptions are correct this would indicate 0% duty cycle, meaning the system isn't attempting to adjust the mixture at all. Does that sound right?
The voltage you read out does indicate 0% duty cycle … but that does not mean that the system isn't attempting to adjust the mixture at all … quite the contrary … it‘s trying its best to adjust the mixture … which seems to be rich beyond the system‘s capability to lean it out via EHA.

For details see: http://www.benzworld.org/forums/w12...49-ke-jetronic-lambda-control-duty-cycle.html

Btw … your entry under occupation in your profile takes me back (35 years) … :wink_2:

H.D.

P.S.: Since, unfortunately, I’m not receiving notifications on threads I’m subscribed to from Benzworld, I might not notice further questions in this or in the above-mentioned thread. … Sorry if that happens.
 
#16 ·
So should I adjust my Lambda control adjustment? I've previously been instructed by a mechanic to never adjust it as he has set it where it needs to be.. Does a 0% duty cycle indicate any potential issues other than running very rich?
Once I get paid I will purchase a new OVP and let you all know how that turns out!
 
#17 ·
... Does a 0% duty cycle indicate any potential issues other than running very rich? ...
If you checked the Lambda control adjustment (at X11 across pins 2 & 3) with a voltmeter and read out “a constant roughly 14.1 to 14.2 volts“ (instead of measuring a duty cycle of 0% with a duty cycle meter), then:
- either the engine is running very rich
- or there‘s a problem with the ECU
- or there‘s a short circuit on the wire to pin 3 of X11

So should I adjust my Lambda control adjustment? I've previously been instructed by a mechanic to never adjust it as he has set it where it needs to be ...
Very good question … much better than rashly changing the Lambda control adjustment when the meter shows a too low/high duty cycle. … And I hope that the mechanic made sure that everything else was in order before he set it.

I suggest to check a few things that might cause the 14 volts (0% duty cycle) reading … starting with measuring voltage, with “igniton on“ (engine not running), between X11 pin 3 & ground … and between X11 pin 6 & ground. The quotient of the pin 3 voltage and the pin 6 voltage should be about 0.3. … If that's the case, the third of the above-mentioned possible causes can be excluded (and the second one is less probable).

The next thing I‘d suggest, is to measure the o2 sensor voltage at the (connected) o2 sensor connector under the passenger side‘s floor panel (green cable). ... 0.8 volts or higher indicate “rich mixture“.
If that‘s the case, I suggest to check the CSV (cold start valve) for tightness.
If the CSV is tight, I suggest to check the fuel pressure.
With your engine running at idle, SP (system pressure) should be about 5.3 - 5.5 bar (77 - 80 psi) and LCP (lower chamber pressure) should be about 0.4 bar (5.8 psi) below SP ! … SP higher than 5.5 bar (80 psi), or LCP more than 0.4 bar (5.8 psi) below SP are possible causes for too rich air/fuel mixture.

Let‘s see the results of these test prior to further suggestions.

H.D.
 
#24 ·
Street cruiser, if you want to know more about Fuel injection details than your mechanic does (even if he is doing the work), I would highly recommend reading H.D. 's write-ups on the subject on BenzWorld. They are simple and concise enough and educational. He has them in W124 as well as W201 and W126 (I believe).

Jetronic FI is better explained in these write-ups than the Bosch manual (in my humble opinion) as I have read both (cause I had to, believe me)

Although I comment on FI related issues in various post, I always refer people to read the Bible (H.D. write-ups) for the whole story.

My 2 cents worth...
 
#25 ·
The OVP relay is a strange critter and I'm not sure exactly how it's wired into the big picture but when one goes bad it does some really weird stuff to the car :eek warning lights flash or come on and off for no reason, car runs differently than "normal". Under a suggestion years ago I replaced the one in the SE (picked a new looking one from a wrecked car) and suddenly, no more flashy lights, good and proper idle, and overall ran better :dunno: :bowdown:
 
#26 ·
The OVP relay is a strange critter and I'm not sure exactly how it's wired into the big picture but when one goes bad it does some really weird stuff to the car :eek warning lights flash or come on and off for no reason, car runs differently than "normal" ...
That lies in the nature of its function ... it provides (limited) supply voltage (battery voltage) for ECU‘s … on the M103 also for the ICV, which is actually also an ECU supply voltage (via ICV) that‘s converted into an adjustable square wave voltage by the CIS-ECU for ICV control.

Fortunately, the OVP is not difficult to check. … I can monitor it (and several other things) during driving with the device shown in the picture in post 22 of http://www.benzworld.org/forums/w12...49-ke-jetronic-lambda-control-duty-cycle.html ... something I recommend enthusiasts of KE-Jetronic equipped cars to think about, BTW. Facilitates diagnosis immensely, especially in case of intermittent problems. … :wink_2:

H.D.
 
#27 ·
CC55, back to your concern since this is your post originally. Looking at your vacuum and comparing to mine, it is not that bad. Your leak may even be on the vacuum gauge side of things (like the vacuum actuators with your HVAC) Mine was like yours a year ago, did not effect the idle or the engine performance in any way. I have fixed the leaks now but I had to get into the dash to do it and I replaced two actuators. The vacuum is adversely effected by your low RPM. At 700RPM you are closer to all the way pegged. You still have one minor leak but again comparing to my engine it should not effect your performance. If you had a MightyVac you could find the instrumentation related leaks very easily. The cost online is about $25 I think.

I'm curious, what month was your M103 born in 1989? Since it has >200K miles I assume after March. Am I correct?
 
#28 · (Edited)
... You still have one minor leak but again comparing to my engine it should not effect your performance ...
A false air leak causes leaner mixture, which is compensated (enriched) by higher EHA current, which is indicated by a higher duty cycle. … The OP, on the contrary, read out a duty cycle of 0% (post 14), which indicates extremely rich mixture (see post 15 & 17) !

Turning the Lambda adjustment screw ccw might lean out the mixture far enough to get Lambda control back to working again, which would be indicated by a fluctuating duty cycle. The duty cycle might even be adjustable back to its proper range if the adjustment screw is turned far enough (should not be turned out of its thread though !) … but that might just compensate for a problem that would continue to exist, which is not recommendable. … The tests mentioned in post 17 are the much better option. … :wink_2:

H.D.
 
#31 ·
Yes, I should have believed you on the OVP H.D. But I figured it was work a shot..

I assume a VIN beginning in CA indicates the car was originally from California?

When performing the o2 sensor test the car may not have been at operating temperature. I'll have to double check the voltage the next time I drive. But I will go ahead with these tests the next time I can! Also, should I still be concerned with testing the fuel pressure?
 
#33 ·
Yes, I should have believed you on the OVP H.D. ...
Be careful, believing people … I might be a loudmouth … (many of‘em out there today :wink_2:) … LOL

I ‘believe‘ that it‘s much better to properly test things to find out what‘s causing a problem, instead of changing things to see if it goes away. … :wink_2:

... When performing the o2 sensor test the car may not have been at operating temperature ...
o2 sensor voltage tests only make sense if done with the engine well at operating temperature !

... should I still be concerned with testing the fuel pressure?
Not yet … let‘s get reliable o2 sensor voltage data first.

Btw, nothing you reported so far indicates a problem with your CTS (coolant temperature sensor) either. … :wink_2:

H.D.
 
#32 ·
Cody have you changed the engine temperature sensor yet . A lot of information is sent to the electronics parts on your engine for it to operate right . If the sensor is stuck, then it could tell the computer its cold ,and in doing so the computer will then richen the mixture up . But can work the other way and make it weak when your engine needs rich mixture ..
 
#36 ·
Open Loop: fluctuated between 750-800 mV
Closed Loop: Fluctuated between 0 -800 mV
Open loop without EHA: fluctuated between 400- 700 mV
Open loop, no EHA, 2500RPM: steady 815, minor fluctuation.

I used the bolt heads used to attach the seat as ground. While taking these measurements the electronics were very finicky, and I got some weird values. Let me know if any of these numbers still seem improbable as I may have made an incorrect measurement
 
#37 ·
... I used the bolt heads used to attach the seat as ground ...
That's okay, but you can also use the battery minus pole.

... While taking these measurements the electronics were very finicky, and I got some weird values ...
… which might also have to do with your meter ... plus, assuming that you‘re using a digital meter, an analog meter is much more comfortable for reading such fluctuating values.

... Let me know if any of these numbers still seem improbable as I may have made an incorrect measurement
These numbers differ significantly form the implausible ones you reported in post 34. … Could it be that in post 34 you measured between both parts of the connector, and not between the o2 signal wire and ground ? … :wink_2:

The numbers you report now, look more plausible and more like what I expected. But you forgot one measurement. Anyway, since these tests are very easily done and you‘re not completely sure if you measured correctly, I suggest to repeat them, with the hot engine running at idle and the ECU connected, in the following order:

Closed loop test (EHA and o2 sensor connector connected):
1) Both parts of the o2 sensor connector ‘somehow‘ connected (diagram #1)

Open loop tests (o2 sensor connector not connected):
2) EHA connected (diagram #2 without ground wire)
3) EHA connected and male part of the o2 sensor connected to ground (diagram #2)
4) EHA disconnected (diagram #2 without ground wire)
5) EHA disconnected and engine speed risen to ~ 2500 RPM (diagram #2 without ground wire)

H.D.
 

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#39 ·
Okay, based on these significantly more plausible o2 sensor voltages, there seems to be a problem
- with the FD‘s (fuel distributor) basic setting via Lambda adjustment screw
- or with the position of the CP‘s (control plunger) lock screw
- or with the AFM‘s (air flow meter) or CP‘s movability
- or with the cleanness of (at least the lower part of) the FD‘s metering slits
- or with the injectors


I suggest not to touch the Lambda adjustment screw, and to do the following test now:

  • First check the AFM plate‘s “zero position“ according to the attached PDF
  • Then let the engine reach operating temperature and switch it off
  • Push the AFM plate slowly & slightly down with your finger and attentively feel the mechanical resistance. On the first 1-2 mm of the plate‘s travel (starting from its correct “zero position“) you should feel almost resistanceless play. The only resistance you should feel along these first 1-2 mm is the one that‘s caused by the AFM‘s counterweight.
  • Then, latest after about 2 mm !, you should feel the other end of the AFM lever reach the CP. Up from that moment the AFM lever pushes the CP (in the center of the FD) upwards, causing you to feel some slight homogenous additional resistance. Additionally to that suddenly starting sensible resistance you should not have to apply any additional break-away force at that point.
  • Up from that moment there should also not be any noticeable resistance jumps along the rest of the AFM plate‘s travel.
  • After having pushed the AFM plate completely down, quickly and completely let go of it ... it must quickly and smoothly jump back into its “zero position“.
  • Then turn the key once or twice to ignition on for as long as you hear the fuel pumps prime.
  • Then push the AFM plate swiftly completely down with your finger again, but this time don‘t let it freely jump completely back. This time let it swiftly jump back in 5-10 mm steps. Hold it at these steps for a moment and feel if the CP is following the AFM lever (with a little delay) … you should feel it reach the AFM lever less than a second later at each step. This way feel if the CP follows the AFM on its incremental way back to its “zero position“ !

If you want to repeat one of these two test steps, first turn the key once or twice to ignition on for as long as you hear the fuel pumps prime.

Furthermore, I have a question: Has the FD ever been removed ?
If so, has the CP’s lock screw (in the center of the FD’s bottom side) ever been touched ?

H.D.
 

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#40 ·
I tried all these tests and they've all been passed, except for centering the plate. I attempted to measure the gap using a basic Napa feeler gauge at .483 mm. The guage is approximately 1 CM across, so I'm having trouble fitting it into the gap due to the curvature. Is there a trick to this test, or are circular feeler gauges (at .5 mm) an option? This was performed first thing in the morning before the car had been driven.

I'm unsure whether the FD has ever been dissassembled.

Additionally, since completing the o2 sensor tests my check engine light has come on. I pulled the code and got 5 blinks. If the chart I'm reading is correct this indicates a fault with the o2 sensor.
 
#41 ·
I tried all these tests and they've all been passed, except for centering the plate ...
Very good … sounds like the AFM and the CP have flawless movability.

... Is there a trick to this test, or are circular feeler gauges (at .5 mm) an option? ...
Probably your feeler gauge doesn‘t taper at its end, right? … Instead of a feeler gauge, you can also use something else, like a needle … or a real good eye :).

... since completing the o2 sensor tests my check engine light has come on. I pulled the code and got 5 blinks. If the chart I'm reading is correct this indicates a fault with the o2 sensor.
I hope you did the o2 sensor voltage tests correctly … especially with the very different and implausible readings you reported in posts #34 and #36 I wonder how you measured that. You did not, for instance, connect the wrong part of the o2 sensor connector (the female part that‘s coming from the sensor, instead of the male part) directly to ground with a wire while you did the tests, did you ? … And you reconnected the connector properly, right ?

Besides the movability of the AFM and the CP and the position of the CP, I mentioned three more possible reasons for your problem in post #39 … (based on the o2 sensor voltages you reported in post #38).
And if these values - especially the value of test #4 - are reliable, I add two more suspects:
- the EHA
- and the restrictor in the FD

I‘ll give you further test suggestions after your feedback about my concerns regarding the o2 sensor tests you did.

H.D.
 
#42 ·
I have not yet tried using another object to measure the gap but I will as soon as I can!

As far as I know I connected the sensor correctly. I did not connect the female plug (coming from the sensor) directly to ground. The results in post 34 were from placing the multi meter directly between the 2 o2 sensor plugs. Yes, the connector is back in place as it was before. I remember a few months ago (6?) The check engine light came on for a day or two but went away before I had the opportunity to check it. Is it possible to reset the light to see if it will come on again?
 
#43 ·
Regarding the check engine light: since only California cars are equipped with it, which I‘ve never been in touch with, I‘m not sure, but I think the light disappears when the problem that caused it is gone.

Experiences in another forum here at Benzworld lead me to address something general:
So far, I have not suggested to replace any parts or readjust anything to see if the problem goes away … I never do that. I suggest and describe systematic testing, especially in case of the KE-Jetronic. So far we have only done some o2 sensor voltage tests … and there are many more and also more informative tests than those shown in Bosch / MB service manuals / books … which, from Bosch‘s or MB‘s point of view is understandable … they suggest(ed) not to test any further up from a certain test level and to buy and install complete new assemblies, like the FD or AFM … :wink_2:

The tests I suggest here at Benzworld are a lot easier to do than it may seem at the first look at detailed test procedures of mine. Plus, systematic testing helps to understand the system and to avoid unnecessary money spending. … I mention these things, because not everybody cares about understanding the system or saving money. Often people just want to get their cars fixed asap, also at the risk of spending more money … and there is nothing wrong with that.

So, depending on each individual situation, following my advice may not be the most suitable way. But if you are interested, I‘ll post further test suggestions to narrow down the possible causes for your specific problem.

H.D.
 
#45 ·
I saw your reply by chance, because I did not get any email notification about it. There was a problem with email notifications over many months this year already. … I hope it‘s not back again !?

Okay codycool55 ... since you‘re interested, I‘ll dive a little deeper into systematic testing than I have done so far here at Benzworld. Maybe a few other readers here in the 126 forum will be interested too. I tried to awaken interest in that in another BW forum not long ago, but practically no one there was interested.

The possible culprits I have mentioned so far (based on your information) are:
- fouled / faulty o2 sensor
- incorrect Lambda control adjustment
- incorrect position of the CP lock screw
- incorrect AFM ‘zero position‘ (checked)
- incorrect AFM play (checked)
- sluggish AFM / CP movability (checked)
- contaminated metering slits
- injectors
- EHA
- restrictor

Based on the assumption that especially the o2 sensor voltage #4 you reported in post 38 and the duty cycle of 0% you reported earlier, which do not match with each other, are reliable … the next thing I would do if I had your car here is something I addressed in post 22 of my KE-Jetronic Lambda control thread:
A simultaneous test of:
- fuel pressure (System Pressure and Lower Chamber Pressure)
- EHA current (ampmeter connected in series between EHA and EHA plug)
- o2 sensor voltage (closed loop, voltmeter connected as shown in diagram 1 in post 37)
- duty cycle (terminal 3 at the diagnostic socket)
with the engine at operating temperature, both at idle speed and at ~ 2500 rpm, once with the EHA electrically connected and once with the EHA electrically disconnected.

That sounds more complicated than it is. When I do such a test, I place all (analog) meters next to each other, and since I can not simultaneously watch fluctuating values on several meters, I let my tablet PC, fixed above the meters, record a video of all readings while I carry out the test steps. After the test I watch the video and stop it at interesting moments for detailed analysis.

That test also shows whether the ECU is telling the truth in ‘duty cycle language‘ about what it is telling the EHA in ‘current language‘. Remember, in my Lambda control thread I said that the “fluctuating duty cycle is an easier to check representative of the EHA current, and the duty cycle check / adjustment is actually an EHA current check / adjustment”.

As a side note:
When I check a KE-Jetronic, I always check / adjust the Lambda control directly via EHA current, not (indirectly) via duty cycle. I just quickly compare the duty cycle with the EHA current at the end, only to see if the ECU‘s duty cycle information at the diagnostic socket is reliable. I also never do the “ignition on / engine off“ duty cycle tests I described in my KE-Jetronic Lambda control thread. Neither do I care about static duty cycle error codes when I check a KE-Jetronic. I use other test routines prior to the Lambda control test, that are not described in any service manual, with selfmade test equipment ... covering all of these and many other things more informatively and more reliably.
The duty cycle I only watch occasionally during driving … on the selfmade OBD ‘ashtray‘ I introduced in my Lambda control thread … which is very helpful in tracing (especially intermittent) problems that are represented by static duty cycle values. ... :wink_2: … I might introduce this OBD device a little more detailed here in the 126 forum when I have a little more time.

H.D.
 
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