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Discussion Starter #1
Hello R129 owners, sometimes I post things in the 124 and 126 forum, and last weekend I wrote up a few things about the KE-Jetronic’s Lambda control adjustment, which perhaps some people here at the 129 forum might find useful too.

Before I get to my suggestion how to check and how to change the KE-Jetronic’s Lambda control adjustment, I’d like to address some basics in this first post, which might help better understand the matter. I’ll continue with some recommendations and considerations and the detailed procedures in post #2.

Basics:

Here at BenzWorld.org I see the Lambda control adjustment usually being called ‘duty cycle adjustment’, or (not really suitably) ‘mixture adjustment’ or ‘air/fuel mixture adjustment’, which can easily lead to (and possibly often reveals) misconception. … By changing the adjustment the position of the fuel distributor’s control plunger in relation to the air sensor plate’s position is changed, which in case of a K-Jetronic (without lambda control) results in a changed ‘air/fuel mixture’, but - aside from the engine’s warm-up phase, or completely floored accelerator, or limp home mode - not in case of a KE-Jetronic!

What is ‘Lambda control’?
It’s the fine-tuning of the air/fuel mixture to a ratio at which complete fuel combustion takes place, in order to minimize pollutants. That ratio is called ‘λ (Lambda) = 1’, which in case of non-ethanol fuel is given at an air/fuel ratio of about 14.7 mass units of air for 1 mass unit of fuel (14.7:1). It’s a compromise between engine torque and fuel consumption. The highest engine torque would be given at a ratio of about 12.5:1, and the lowest fuel consumption would be given at a ratio of about 16:1.

How does Lambda control work?
I like to use a metaphor for illustration. While driving along the road our eye tells our brain to which side the car is about to drift off-lane, the brain processes that information and tells our hand to turn the wheel a little to the left or to the right, which we more or less alternately do all the time. … Translated to the KE-Jetronic the lane is ‘λ = 1’, the eye is the o2 sensor, the brain is the ECU (electronic control unit), and the hand is the EHA (electro-hydraulic actuator).
The EHA is a valve via which fuel flows through the lower chambers of the fuel distributor’s pressure differential valves in order to control the quantity of fuel injection, hence the air/fuel mixture. The EHA’s baffle plate is electromagnetically moved closer to or further away from its inlet nozzle by positive or negative current from the ECU, by which the lower chamber pressure can be changed. And the lower chamber pressure controls the fuel flow through the upper chambers, each of which has a separate injector pipe port.
In order to detect whether complete fuel combustion is taking place, regardless of the type of fuel, the o2 sensor compares the amount of residual oxygen in the exhaust gas with the amount of oxygen in the ambient air. At the ratio which represents complete fuel combustion (λ = 1) the o2 sensor is very sensitive and generates a voltage of 450 mV. That voltage changes significantly at tiny changes of the oxygen ratio. At ‘λ = 0.98’ the o2 sensor voltage is about 800 mV, and at ‘λ = 1.02’ it’s about 100 mV. And as we can not keep the car in its lane without tiny adjustments via steering wheel, ‘λ’ can not be kept at ‘1’ without tiny mixture adjustments either. The air/fuel mixture is either a touch too lean or a touch too rich and alternately has to be enriched and leaned a touch (micro-tuned) in order to keep ‘λ’ close to ‘1’. Lambda fluctuates with about +/- 0.02 around 1, when the o2 sensor voltage fluctuates with about +/- 350 mV around 450 mV, which with a healthy o2 sensor hapens at a cycle frequency of about 0.5 – 1 Hz. That’s the o2 sensor voltage the ECU ‘wants’ to receive, and it adjusts the air/fuel mixture via EHA control in such a way that it does receive that voltage, regardless of the kind of fuel, which in case of non-ethanol fuel leads to an a/f mixture fluctuating with about +/- 0.3 around 14.7:1. In case of ethanol containing fuel it leads to a different (richer) mixture, depending on the percentage of ethanol in the fuel.
Here’s a simplified example of one Lambda control cycle with non-ethanol fuel, which takes about 2 seconds at idle:
- λ ~ 0.98, (a/f ~ 14.4:1), > o2 sensor voltage to ECU ~ 800 mV
- ECU generates more negative EHA current (duty cycle: 45%)
- leaning the air/fuel mixture
- λ ~ 1.02, (a/f ~ 15:1), > o2 sensor voltage to ECU ~ 100 mV
- ECU generates more positive EHA current (duty cycle: 49%)
- enriching the air/fuel mixture
- next cycle: λ ~ 0.98, (a/f ~ 14.4:1), > …..

What happens when we change the Lambda control adjustment?
Let’s say the duty cycle is fluctuating like in the above example between 45% and 49% at idle. When we change the adjustment by turning the adjustment screw cw the control plunger moves to a higher position, leading to a richer mixture. That immediately leads to o2 sensor voltage not undershooting 450 mV, upon which the ECU immediately reacts with an EHA current fluctuating around a more negative mean value in order to lean the mixture again, which is accompanied by a duty cycle fluctuating, for example, between 33% and 37%.
And when the control plunger is set to a lower position by turning the adjustment screw ccw, leading to a leaner mixture, the o2-sensor immediately reacts with voltage not overshooting 450 mV, upon which the ECU immediately reacts by sending a current fluctuating around a more positive mean value through the EHA’s coil in order to enrich the mixture again, which is accompanied by a duty cycle fluctuating, for example, between 57% and 61%.
No matter to which position the control plunger is set, unless it’s set too high by cw turns beyond the EHA’s ‘Lambda leaning limit’, or too low by ccw turns beyond the EHA’s ‘Lambda enriching limit’, the ECU always adjusts the air/fuel mixture via EHA control, regardless of the kind of fuel, in such a way that it receives o2 sensor voltage that fluctuates with about +/- 350 mV around 450 mV, which represents ‘λ ~ 1 +/- 0.02’ respectively ‘a/f ~ 14.7 +/- 0.3 : 1’ (in case of non-ethanol fuel).
Or, speaking in terms of ‘duty cycle’: No matter around which mean value the duty cycle fluctuates, as long as it’s above 5–10% (‘leaning limit’) and below 90–95% (‘enriching limit’), if it fluctuates, Lambda respectively the air/fuel mixture fluctuates around the correct ratio, intactness of the system provided, of course. However, around (or close to) 50% it does that more precisely than, for example, around 20% or 80% (I’ll get back to that in post #2).
Conclusion: When we change the duty cycle adjustment we change the operating ranges of both the control plunger and the EHA’s baffle plate … but not the mixture!
- Control plunger higher > EHA more open
- Control plunger lower > EHA more closed

What’s this ‘duty cycle’ about?
Parallel to the fluctuating EHA current the ECU sends a square wave voltage with a corresponding ‘on/off ratio’ to port 3 of the diagnostic coupling X11, where it can be measured in 'duty cycle', 'dwell angle' or 'volt'. This 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.
A duty cycle of 50% represents an EHA current of ‘0’ mA, a duty cycle below 50% represents negative current (flowing in one direction through the EHA’s coil), and a duty cycle above 50% represents positive current (flowing in the other direction through the EHA’s coil).
Additionally to the fluctuating duty cycle, a non-fluctuating (static) duty cycle while the engine is running serves as error code.

From the above it may also become clear that the air/fuel mixture can not only be ‘micro-adjusted’ (to ‘λ ~ 1 +/- 0.02’) via EHA control, as often assumed, but also ‘macro-adjusted’ - as long as the EHA’s leaning / enriching limits are not exceeded. Especially the leaning capability via EHA control is significant, and more precise.
Let me illustrate this ‘macro-adjustment’ with my driving-along-the-road metaphor:
As explaned above, the ‘micro-adjustment’ via EHA control is like the constantly done tiny adjustments via steering wheel to the left and right in order to keep the lane, no matter whether we’re driving along a straight road or through a curve. The ‘macro-adjustment’ is like the turning of the steering wheel in order to follow the road’s changed direction. The changed direction of the road represents a changed condition of the system … for example, a changed control plunger position in relation to the air sensor plate, or different fuel, or contamination in the fuel distributor, or a false air leak (of limited size of course), etc. …. conditions, all of which without EHA control would result in more or less significantly too rich / lean mixture.
The more or less far to the left or right turned steering wheel represents the EHA’s baffle plate position more or less far away from the EHA’s inlet nozzle, respectively an EHA current more or less far below or above ‘0’ mA, respectively a duty cycle more or less far below or above 50%.
And like we continue with the tiny adjustments of the steering wheel to the left and right in order to keep the lane, no matter whether we hold the steering wheel in the straight-ahead position on a straight road or turned to the left or to the right in a curve, the ECU continues with the tiny adjustments of the EHA’s baffle plate in order to keep ‘λ ~ 1 +/- 0.02’, no matter whether the baffle plate is operating closer to or further away to either side from its center position (closer to or further away from the EHA’s inlet nozzle).

Continued in post #2 …
 

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Discussion Starter #2 (Edited)
... continuation of post #1

Purpose of the adjustment:

Since, as I explaned in post #1, the air/fuel mixture is unchanged, no matter whether the system is adjusted to a higher or to a lower duty cycle … what is the purpose of the adjustment?
It’s the EHA’s optimal operating range with regard to:
- Lambda control (keeping ‘λ ~ 1 +/- 0.02’ by fine-tuning the air/fuel mixture)
- the engine’s running behavior.

Regarding Lambda control the EHA’s optimal operating range is given when its baffle plate oscillates around its center position (currentless rest position) – in other words, when the EHA current fluctuates around ‘0’ mA, which is represented by a duty cycle fluctuating around 50%. That way the EHA has its highest dosage accuracy.

Regarding running behavior, however, a slightly further opened EHA with its current fluctuating around a mean value slightly below ‘0’ mA at idle, which is represented by a duty cycle fluctuating around a mean value slightly below 50%, is better. That has i.a. to do with the in post #1 mentioned better leaning than enriching capability of the EHA. A duty cycle at idle fluctuating around a mean value of about 47% or a little lower is usually a good choice for an intact KE-Jetronic in my experience.

I’d like to add that there’s another advantage of a duty cycle close to 50%, respectively of an operating range of the EHA’s baffle plate close to its currentless rest position. That way the air/fuel mixture is almost unchanged if the KE-Jetronic goes into limp home mode due to a failure of the ‘E’ in ‘KE-Jetronic’, and during driving at normal operating temperature most drivers would probably not even notice any change.
That, btw, was a major argument in favor of the KE-Jetronic (as an advanced K-Jetronic) for Mercedes, at a time when BMW was already using the fully electronic L-Jetronic. They did not want to see pictures and reports in the media about S-Classes standing on Autobahn brakedown lanes due to injection system problems ever again either, which they did with the fully electronic D-Jetronic they introduced in the early 70s. Instead they prefered the owner to drive quietly to the dealership and tell the friendly people there that somehow the car behaves strangely for a minute or two after starting it in the morning ... lol.


Please note:

Above target values apply to an intact system (not only CIS) !
Generally problems relevant for the fuel combustion have an influence on the EHA control, hence on the duty cycle. Depending on the problem(s), the most suitable duty cycle could, for instance, be below 30% or above 70%.

Here are a few examples of relevant problems:
Oil or coolant getting into the combustion chamber(s), wrong or bad spark plugs, bad distributor cap/rotor, worn injectors, leaking cold start valve, contaminated metering slits in the fuel distributor, incorrect fuel pressure, false air leaks, clogged air filter, incorrect ignition timing / faulty vaccum advance, false input from o2 sensor, problems with the ECU, EHA’s baffle plate damaged, EHA’s coil damaged (resistance should be 18–21 Ω), incorrectly adjusted throttle linkage, throttle plate not resting against its idle stop, air sensor plate not centered or its ‘zero position’ incorrect, control plunger sluggish or stuck, problem with EGR valve, bad battery, bad voltage regulator, …

On the other hand, a duty cycle check might help to track such problems. A high duty cycle might be caused, for example, by a false air leak, which of course should be fixed instead of turning the duty cycle lower with the adjustment screw. A low duty cycle might be caused, for example, by a leaking cold start valve, which of course should be fixed instead of turning the duty cycle higher.

Correcting the duty cycle to the target value is often done too easily, IMHO, and should only be done if the elimination of the reason for its deviation is an option which doesn’t come into consideration, like maybe for instance in case of a problem inside the fuel distributor.
But, checking the duty cycle is too often neglected as a quicky and easily done diagnostic measure, IMO.

The kind of fuel being used (non-ethanol / ethanol-containing) has no effect on the validity of the above EHA current / duty cycle target values (see ‘Basics’ in post #1). However, it has of course an effect on the position to which the control plunger has to be set (via adjustment screw) in order to get to these values !
After a switch between fuel types, depending on the o2 sensor’s input, the ECU sends different amperage through the EHA in order to change its operating range, accompanied by a correspondingly different duty cycle, so that it continues to receive o2 sensor input fluctuating around 450 mV (which represents ‘λ ~ 1’). Therefore after a switch between fuel types the duty cycle should be checked, and if necessary readjusted to the target values !

I’d also like to point out, that the duty cycle adjustment does not ensure corresponding optimal results if the adjustment of the EHA’s baffle plate has been improperly changed !
Changing the EHA’s adjustment can make sense in case of a changed fuel distributor condition. There could, for example, be contamination, or the pressure differential valve’s diaphragms / springs may have been replaced and differ from the original ones, etc.. But bear in mind that by changing the EHA’s adjustment the mechanically predetermined fuel flow rate through the lower chambers of the pressure differential valves in relation to the fuel flow rate through the meetering slits into the upper chambers is changed, which IMO should not be done without adequate know-how and care. If done improperly the EHA current’s / duty cycle’s informative value is gone! … and it’s proper adjustment, as for instance also required for other tests, impossible !


Measuring device:

I suggest to either use an analog duty cycle meter or an analog voltmeter. Analog meters offer more comfortable monitoring of the fluctuating readings than digital meters.

Duty cycle meter:
Some duty cycle meters show the percentage of the square wave voltage’s ‘on’-time, and others show the percentage of its ‘off’-time. In case of the KE-Jetronic the duty cycle value refers to the square wave voltage’s ‘off’-time. A meter which shows the ‘on’-time would, for instance, read 53% instead of the relevant 47%.
If you’re not sure which version your meter is: With ignition switched on (engine not running) the duty cycle should be about 70% (California: 85%). If the meter shows about 30% (California: 15%), it’s probably the wrong version. And if, while the engine is running, the fluctuating duty cycle drops when the adjustment screw is turned cw, it’s the right version.

Voltmeter:
The voltage is converted to duty cycle according to the following formula:
duty cycle [%] = [1 - (Vp3 / Vp6)] * 100
Vp3 = voltage between X11 port 3 & port 2 (or ground)
Vp6 = (battery) voltage between X11 port 6 & port 2 (or ground) during the respective rev !
Example for a measurement at idle:
Vp3 (at idle): 7.1 - 7.6 V
Vp6 (at idle): 13.9 V
duty cycle at 7.1 V = [1 - (7.1 / 13.9)] * 100 = 48.9%
duty cycle at 7.6 V = [1 - (7.6 / 13.9)] * 100 = 45.3%
duty cycle mean value: (48.9% + 45.3%) / 2 = 47.1% (fluctuating with +/- 1.8%)


Preparations:


  • In case of California version the ECU may have to be switched over to duty cycle output. Check the service manual for instructions if necessary.
  • Warm up the engine to its normal operating temperature. A 10-minute warm-up drive is better than letting the engine idle until it’s warm. Make sure that the engine does not heat up too much during the check / adjustment procedure.
  • Pull off the vacuum line between the throttle valve and the regeneration valve of the fuel evaporation system at the regeneration valve and block it.
  • Keep the A/C switched off.
Check procedures:


  • Connect the meter to the diagnostic coupling X11 port 3 and 2 (or ground).
  • With ignition switched on (engine not running) the duty cycle should be about 70% (California: 85%).
    If you’re using a voltmeter it should read 0.3 * Vp6 (California: 0.15 * Vp6)
  • Take off the air filter lid and check two other duty cycle values with ignition switched on (engine not running):
    With the throttle closed and the air sensor plate deflected the duty cycle should be about 10%. If it stays at 70% there may be a problem with the ‘closed signal’ of the throttle position sensor.
    With the throttle fully opened and the air sensor plate not deflected the duty cycle should be about 20%. If it only drops to 40% there’s a problem with the air flow potentiometer.
    Put the air filter lid back on for the duty cycle check with the engine running, which should be done with the air filter installed (and clean)!
  • Start the engine, let it idle and wait until the reading starts to fluctuate (it takes a moment until the o2-sensor reaches its operating temperature). If it doesn’t start to fluctuate after a while, the meter may be displaying a static error code (see ‘Static duty cycle’ further down).
  • Increase the engine’s speed and monitor the meter while you keep the speed at about 2500 rpm. The reading should fluctuate! Record the values between which it fluctuates – it should be a range not much bigger than 4%, for instance: valley = 42%, peak = 46% (mean value = 44%). The fluctuation frequency (1 cycle = from ‘valley’ to ‘peak’ and back to ‘valley’) should be about 1 Hz (1 cycle per second).
  • Then check the reading at idle. Again it should fluctuate, and again record the values between which it fluctuates. The fluctuation frequency should be about 0.5 Hz (1 cycle per 2 seconds).
  • The mean value at idle should not differ by more than +/- 10% from the mean value at 2500 rpm.
Adjustment procedures:


  • Remove the plug from the adjustment tower (if it’s still in there), so that the Allen wrench can be inserted. You can put a drop of oil into the adjustment tower if you like.
  • Then start the engine, let it idle and wait until the reading starts to fluctuate again.
  • Please note: adjustments are always done at idle (not at the higher rev)!
  • Then insert a 3 mm Allen wrench into the spring-loaded adjustment pin in the adjustment tower and carefully push it down. Don’t put too much pressure on it, otherwise the air sensor plate’s lever below the adjustment pin might be pushed down, which can easily stall the engine. With the Allen wrench engaged, turn the adjustment pin a little to and fro in order to let it snap into the actual adjustment srew, which is located in the air sensor plate’s lever.
  • Turn the adjustment srew in small steps. Even tiny turns can change the duty cycle by several percent.
    Cw turns lower the duty cycle … ccw turns raise the duty cycle.
  • After each step briefly rev the engine and let it settle for about 10 seconds before taking readings.
  • I recommend to record the total adjustment angle. If you turn the adjustment srew too far the engine will stall. And if you can not remember how far and in which direction you have turned it, you may not get the engine restarted. Then the KE-Jetronic needs to be reset in order to get the engine started again, which is not very difficult, but unnecessary labor.
  • After the adjustment to the desired value at idle, check the duty cycle at 2500 rpm and then again at idle.
    Readjust if the mean value difference between both engine speeds exceeds the above-named allowance.
Static duty cycle:

A static (not fluctuating) duty cycle value with the engine running and the o2-sensor at operating temperature, indicates a problem according to the following list:

  • 0%: problem with the meter
    or diagnostic coupling (X11)
    or too rich setting (beyond the EHA’s ‘leaning limit’)
  • 10%: TPS (throttle position sensor), throttle fully closed signal
    or (if at 2.000 rpm) no/false supply voltage to POT (air flow potentiometer)
  • 20%: TPS, ‘throttle fully open’ signal
  • 30%: CTS (coolant temperature sensor)
  • 40%: no/false output voltage from POT
  • 50%: o2 sensor (aside from not having reached its operating temperature yet)
  • 60%: car speed signal (displayed during driving or engine still running after driving)
  • 70%: CPS (crankshaft position sensor)
    or EZL (electronic ignition module)
  • 80%: IATS (intake air temperature sensor)
  • 95%: micro switch of throttle linkage (6-cylinder engines)
  • 100%: problem with the meter
    or diagnostic coupling (X11)
    or ECU ‘N3’ (missing connection to voltage supply or to ground)
    or OVP (overvoltage protection relay)
    or o2 sensor signal (short to ground)
    or too lean setting (beyond the EHA’s ‘enriching limit’)
Consider that in case of a static duty cycle reading, there may be just a problem with the connection of a component (loose / broken cable, damaged plug) instead the component itself.

Depending on the running behavior after duty cycle readjustment an additional EHA check which includes overrun cut-off and acceleration enrichment and lower chamber fuel pressure tests under various engine operating modes may be recommendable.

Don’t forget to reconnect the vacuum line of the fuel evaporation system!

H.D.
 

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Excellent and comprehensive write-up! I would recommend you also post in the R107 forum, many 560 SL owners there with KE. They'll love it :)
 

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Discussion Starter #4
Thank you very much Ruindr, also for reminding me to post this in the R107 forum. I didn’t have enough time today, maybe tomorrow morning. It’s not only relvant for the 560 (M117) of the R107, but also for the 500 (M117), the 420 (M116) and the 300 (M103).
 

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DUTY CYCLE COMMENTS

Hello H.D.
I liked your post. Very good. :thumbsup:

There are two fuel system adjustments: -

1) Lambda control (duty cycle), which is controlled electronically by the CIS-E computer (N3), and

2) The fuel pressure differential between the upper and lower chambers of the fuel distributor, which should also be checked.

Whilst aside from WOT and limp home mode the M119 lambda control is enabled once the post start enrichment is completed, for the M103 lambda control operates in open-loop mode, and then after max of 2 mins returns to closed-loop.

The duty cycle adjustment is the lambda control adjustment but I also like to think of it as the baseline KE setting.

When we change the baseline setting we change the operating window of both the control plunger and the EHA, as you say … BUT we do in fact also change the mixture (air-fuel ratio) under limp home mode, warm up phase, and full load (WOT).

Why is the baseline setting important to R129 owners?

The baseline setting can have a significant effect on the startup characteristics, and also the engine responsiveness and torque during warm up and WOT.

On an intact KE system the M119 is slightly harder to start up when the KE average baseline is set too high i.e. 60%. Too low (40%), the idle will be lumpy for the first 15secs, depending on air temp. Max torque at WOT and good cold start characteristics can be obtained with an average baseline setting around 46-48%. A baseline of 50% will give you the smoothest hot idle, with very little oscillation of tune (the 1Hz rhythmic fluctuation due to EHA influence on engine tune). This is where the EHA reed valve is mostly in rest position (0 mA).

In a correctly functioning KE set up, adjustment of the EHA valve adjuster (only possible by removing EHA valve and screw plug) would render the EHA incompatible with the output current from the KE control unit (N3). The EHA valve is factory set to align with the predefined mechanical differential offset between the upper and lower chambers of the distributor. It may be more appropriate, if you are having running issues, following replacement of the injectors or fuel distributor etc, to adjust the KE trimming plug using one of the seven tuning presets.

This brings me on to removing the KATs. Some time ago I thought about doing this (but in the end I decided not to). The KE Jetronic control module (N3) contains 2 fuel maps (or programmes). The choice of fuel programme is determined by the trimming plug fitted (KAT or ECE). One type instructs N3 to adopt lambda control for engines with a KAT, the other for engines without a KAT and no lambda control. For those who wish to remove their KATs, it would seem relevant also to change the trimmer plug, unless of course you find a way to preserve the O2 sensor.

Regards
Rob
 

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Discussion Starter #6 (Edited)
Thank you very much for your comments, Rob.

About 30 years ago I spend a day and a half in the beautiful town of Stratford-upon-Avon … probably not far from your home I guess ... had a good time with locals in one of those nice traditional pubs there. I could picture us chatting about the KE-Jetronic over a few ale in such a place … lol

There are two fuel system adjustments: -
1) Lambda control (duty cycle), which is controlled electronically by the CIS-E computer (N3), and
2) The fuel pressure differential between the upper and lower chambers of the fuel distributor, which should also be checked.
Of course … and that’s not all. There are several other things that can / should be checked on a KE-Jetronic. But this thread is about what its title says, the ‘Lambda control (duty cycle) adjustment’, and I’d like it to stay limited to that. I’m planing to talk about other things, including the fuel pressure, later … in separate threads … when I have more time again. :)

The duty cycle adjustment is the lambda control adjustment but I also like to think of it as the baseline KE setting.
Very good, Rob ... I’m completely with you there … that’s what we usually call it in Germany too: “KE-Grundeinstellung”

When we change the baseline setting we change the operating window of both the control plunger and the EHA, as you say … BUT we do in fact also change the mixture (air-fuel ratio) under limp home mode, warm up phase, and full load (WOT).
That’s exactly why I wrote the second sentence in post 1 under ‘Basics’ the way I wrote it:
<Quote>
By changing the adjustment the position of the fuel distributor’s control plunger in relation to the air sensor plate’s position is changed, which in case of a K-Jetronic (without lambda control) results in a changed ‘air/fuel mixture’, but - aside from the engine’s warm-up phase, or completely floored accelerator, or limp home mode - not in case of a KE-Jetronic!
<Unquote>

The baseline setting can have a significant effect on the startup characteristics, and also the engine responsiveness and torque during warm up and WOT.
On an intact KE system the M119 is slightly harder to start up when the KE average baseline is set too high i.e. 60%. Too low (40%), the idle will be lumpy for the first 15secs, depending on air temp. Max torque at WOT and good cold start characteristics can be obtained with an average baseline setting around 46-48%. A baseline of 50% will give you the smoothest hot idle, with very little oscillation of tune (the 1Hz rhythmic fluctuation due to EHA influence on engine tune). This is where the EHA reed valve is mostly in rest position (0 mA).
That’s correct additional detailled information to where I said (in post 2) that the purpose of the adjustment is the EHA’s optimal operating range with regard to Lambda control and the engine’s running behavior.

However, I’d rather say “This is where the EHA’s baffle plate oscillates mostly close around its rest position (0 mA)” instead of “is mostly in rest position (0 mA)”.

In a correctly functioning KE set up, adjustment of the EHA valve adjuster (only possible by removing EHA valve and screw plug) would render the EHA incompatible with the output current from the KE control unit (N3). The EHA valve is factory set to align with the predefined mechanical differential offset between the upper and lower chambers of the distributor.
Without going too deep into details … the currentless EHA is factory set to a specific volume flow rate through itself, and with it installed the fuel distributor is calibrated to a specific volume flow rate through the metering slits (from the control plunger side into the upper chambers, hence to the injectors) with the control plunger at a specific position and the EHA’s baffle plate in its currentless rest position.
That, btw, was done at the Bosch factory (not by Mercedes) with the completely assembled fuel distributor, so that all involved components (control plunger, metering slit carrier, complete pressure differential valves, etc.) with their production tolerances were included.

Because the fuel flow rate through the metering slits (while the EHA’s baffle plate is in its currentless rest position) is changed if the EHA’s baffle plate adjustment is changed, the ECU (N3) has to provide different EHA amperage in relation to the amount of fuel being injected, in order to ‘be happy’ with the o2 sensor’s feedback. That, of course, comes along with a correspondingly different duty cycle. And that’s why I said in post 2, that if changing the EHA’s adjustment is ‘done improperly the EHA current’s / duty cycle’s informative value is gone!’

H.D.
 

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Hello HD and hello All,

Sorry to crash in on this thread but I should like to ask one question.

My KE-Jetronic is working really well, even with my "by ear" adjustments. Idle is smooth, as is overall performance. For this reason, I am trying not to fix what isn't broken.

There is one thing.

When I start the car (cold/warm/hot) it only starts after about 1 second of cranking. After that, it settles into a smooth idle. No real problem.

However, I should love to restore that "instant start" I remember.

Do you have any ideas what might be the cause?

Non-return valves on fuel pump(s)?
Fuel accumulator (a new part, installed a few years ago)?
Fuel pressure regulator (rather an expensive part!!!).

My thanks in advance.

RayH
 

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Discussion Starter #8
When I start the car (cold/warm/hot) it only starts after about 1 second of cranking. After that, it settles into a smooth idle. No real problem.
Besides checking what this thread is about (the duty cycle), which, IMO, is too often neglected as a quick & easy diagnostic measure anyway (especially after ”by ear” adjustments) … I’d check the fuel pressure, particularly the holding pressure. What you describe sounds (aside from somewhat acceptable for a quarter century old car) like a fuel pressure issue. I’ve seen several cases like that where new check valves at the fuel pump(s) made a difference.
H.D.
 

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I’d check the fuel pressure, particularly the holding pressure. What you describe sounds (aside from somewhat acceptable for a quarter century old car) like a fuel pressure issue. I’ve seen several cases like that where new check valves at the fuel pump(s) made a difference.
H.D.
My thoughts exactly.

I have carefully measured duty cycle and it is set to about 50%, the precise value changing as it should. When I say, "By ear", I mean that I set it at about 53%+- because it was better (than 50%+-) that way. And I am very happy with the result.

I have 2 new check valves and shall get those fitted soon.

I do not have the tools to measure fuel pressure and I am deep in the French country with no Bosch KE specialists near by.

Thank you again.

RayH
 

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Discussion Starter #10
You’re welcome, RayH.
I have 2 new check valves and shall get those fitted soon.
If it is the check valves, it’s indeed both check valves.
But your slight start hesitation might also be caused by worn injectors … just to name one of several other possible reasons ... which, btw, can also be (not necessarily is) the reason for the car’s better running behavior with a rather higher than lower duty cycle.

A fuel pressure test might bring more insight.
I do not have the tools to measure fuel pressure and I am deep in the French country with no Bosch KE specialists near by.
Like checking the duty cycle, checking the fuel pressure is a standard diagnostic measure on a KE-Jetronic, and all you need for complete pressure tests (system~, holding~, lower chamber~) you can get in any well-stocked hardware store for about 25 € … well, for some of the lower chamber pressure tests you would also need a 2.5 kΩ axial lead resistor for a few cent … and it’s not as complicated as it may sound. … I’m thinking about creating a thread about it when I have more time again.

Greatings deep into the French country, which I always enjoy driving through. :)

H.D.
 

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My thoughts exactly.

I have carefully measured duty cycle and it is set to about 50%, the precise value changing as it should. When I say, "By ear", I mean that I set it at about 53%+- because it was better (than 50%+-) that way. And I am very happy with the result.

I have 2 new check valves and shall get those fitted soon.

I do not have the tools to measure fuel pressure and I am deep in the French country with no Bosch KE specialists near by.

Thank you again.

RayH
Assuming all other parts of your fuel system are in spec, and there is no reason why they shouldn't be, your duty cycle looks to be about 5% too high for optimum cold start characteristics. I would adjust it to average 50% and test start again, and then 48% and then recheck start. You may be surprised to find the optimum start is round 48%. It is very sensitive to these things. But stick with whatever suits you. :)

... I’m thinking about creating a thread about it when I have more time again... H.D.
Yes, please do. Whilst checking the holding pressure is a relatively simple procedure, I would like to hear your recommendations H.D. on both this and fuel pressure measurements.

Thank you for your response to my previous comments.

I think I should clarify a point I made. When I said that "aside from WOT and limp home the lambda control is enabled". Note I say lambda control not lambda sensor. At WOT the lambda sensor is still sending a signal. The throttle switch and air flow sensor potentiometer signals N3 about engine load. If N3 detects an increasing airflow and a wide open throttle, the current to the EHA is increased, the mixture enriched and the lambda sensor is ignored. So the lambda control is disabled at WOT.

...Greatings deep into the French country, which I always enjoy driving through. :)...H.D.
Moi aussi!! :grin
 

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If it is the check valves, it’s indeed both check valves.
But your slight start hesitation might also be caused by worn injectors … just to name one of several other possible reasons ... which, btw, can also be (not necessarily is) the reason for the car’s better running behavior with a rather higher than lower duty cycle.

A fuel pressure test might bring more insight.

Like checking the duty cycle, checking the fuel pressure is a standard diagnostic measure on a KE-Jetronic, and all you need for complete pressure tests (system~, holding~, lower chamber~) you can get in any well-stocked hardware store for about 25 € … well, for some of the lower chamber pressure tests you would also need a 2.5 kΩ axial lead resistor for a few cent … and it’s not as complicated as it may sound. … I’m thinking about creating a thread about it when I have more time again.

Greatings deep into the French country, which I always enjoy driving through. :)

H.D.
I have both check valves and both will be replaced.

Also, all injectors were replaced last year. €500 well spent on injectors, guides and seals. This alone returned the car ALMOST to perfect responses.

Only that "IMMEDIATE START" remains to be fixed.

As was said before, this is a 25 year old car. Should I expect perfection? I am a bit crazy about small things like that. I am happy that the car looks old, but I am crazy about things not working 100%.

And yes, France has the roads where you can really enjoy driving. Germany is not the fun it used to be and is much more crowded than France. UK is just mad mad mad, unless you're way away from the south east.

We were in Spain and Portugal last year. Wonderful. Endless Autobahn apparently built just for me. Sadly, many speed cameras. Ironic as my job sometimes involves writing about speed cameras!!!

Best to all.

RayH
 

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Discussion Starter #13
... When I said that "aside from WOT and limp home the lambda control is enabled". Note I say lambda control not lambda sensor. At WOT the lambda sensor is still sending a signal. The throttle switch and air flow sensor potentiometer signals N3 about engine load. ...
Correct.

... If N3 detects an increasing airflow and a wide open throttle, the current to the EHA is increased, the mixture enriched and the lambda sensor is ignored. ...
Please allow me to change that sentence a little and state more precisely:

"If N3 detects an increasing airflow while the coolant temperature is below 80°C or a wide open throttle, the current to the EHA is increased, the mixture enriched and the lambda sensor is ignored."

The degree of acceleration enrichment depends not only on the potentiometer signal, but also on the coolant temperature signal. The higher the temperature – the lower the enrichment. And up from a coolant temperature of 80°C there is no more acceleration enrichment.

That's why the cold engine’s running behavior is so lousy in case of limp home mode, while at operating temperature most drivers are not aware of the CIS being in limp home mode.

... So the lambda control is disabled at WOT. ...
Yes … and always.
 

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Hello H.D.

As I am sure it is getting to be cold in Germany, how I wish you were planning on vacationing for the Christmas holidays in a more warmer climate like this:
:grin:grin

So than if you do decide to fly in, maybe I can pick you up and have you go check the duty cycle on my M119.960 R129 :wink ..... being that I am "technically challenged" :eek::eek:

So may I request you to please find the time to "
... I’m thinking about creating a thread about it when I have more time again... H.D."

:thumbsup:
 

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Hello H.D.
As I am sure it is getting to be cold in Germany, how I wish you were planning on vacationing for the Christmas holidays in a more warmer climate like this ...
So than if you do decide to fly in, maybe I can pick you up and have you go check the duty cycle on my M119.960 R129 ..... being that I am "technically challenged" ...
Haha … thanks for the suggestion, Chicky ... Germany’s Christmas weather can indeed not compete with what I see in that video. :)

For a quick duty cycle check just follow the three chapters ‘Measuring device’, ‘Preparations’ and ‘Check procedures’ in post 2 ... it’s easier than it may sound.
If idle and/or acceleration are okay you don’t even have to do the two tests with the air filter lid removed (third step under 'Check procedures')

H.D.
 

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...Please allow me to change that sentence a little and state more precisely:

"If N3 detects an increasing airflow while the coolant temperature is below 80°C or a wide open throttle, the current to the EHA is increased, the mixture enriched and the lambda sensor is ignored."...
Thank you for expanding regarding normal running conditions, which I agree. My context was at WOT, when the fuel enrichment is not dependent on the feedback from the lambda sensor.

I will take this a bit further, if I may, but along the lines of RayHennig's query regarding slightly poor start.

When the engine is cold, some of the fuel condenses on the side walls of the inlet tracts and mixing chamber, before getting to the combustion chamber, which would (if not addressed) create a lean mixture in the combustion chamber during starting. The cold start valve was Bosch's work around to this problem by injecting fuel directly in to the secondary air system and this enhanced fuel-air mixture is is drawn in to the combustion cycle via the air inlet shrouds around the injectors. The cold start valve does not do all the work alone, and relies on the fuel also supplied by the distributor.

My point is, in older engines the side walls of the inlet tracts become glazed with fuel and combustion products. The glazing/combustion products adsorb fuel particles when cold more readily than new alloy. In an older engine, a bit more of the fuel which is in suspension in the air-fuel mixture coalesces and condenses on the side walls, making the cold start mixture a bit leaner and naturally making the cold starts on older engines not quite as efficient as they were when new.

In addition, a leaner mixture, as we know, increases the voltage required across the distributor points (which is normally around 30kV under normal conditions) to create the initial spark, which leads to an incomplete burn, which accentuates the difficulty in starting from cold. This is one of the reasons why the KE baseline (duty cycle) should be set slightly more 'richer' on older engines, around 48%. The other reason as you say is compensating for the different lean and enrichment characteristics of the EHA.

There are other scenarios which also increase the P.D. required to initiate the spark - wrong spark plugs, too high impedance in wires, bad earthing etc. These, in whatever combinations they occur, lead to a higher energy spark in the spark plug distributors, which can then cause fouling of the points in the DC due to oxidation and can lead to some of the common running problems of these CIS-E engines.
 

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Thank you very much. That makes very interesting reading, as does the rest of this thread.

In my more sensible moments, I face the fact that a 25 year old car cannot be expected to start as it did when new. I shall fit the (cheap) new check valves and possibly get a specialist in the UK to check pressures in the system when I'm next in the UK.

This car is just a hobby for me and I get almost as much fun from this sort of "remote diagnostics" as I do from driving the car. My other hobby is thwarting MB's aggressive pricing policy by finding great deals on genuine parts on the Internet.

My best to all.

RayH
 

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Discussion Starter #18
… along the lines of RayHennig's query regarding slightly poor start.
When the engine is cold, some of the fuel condenses on the side walls of the inlet tracts … cold start valve … air inlet shrouds around the injectors … in older engines the side walls of the inlet tracts … adsorb fuel particles when cold more readily than new alloy … making the cold start mixture a bit leaner … increases the voltage required across the distributor points … which accentuates the difficulty in starting from cold … one of the reasons why the KE baseline (duty cycle) should be set slightly more 'richer' on older engines, around 48% …
Correct. … Btw, you can certainly not be blamed for not having done your homework, Rob. :)

But .. Gentlemen .. don’t forget what’s written in post 7: “When I start the car (cold/warm/hot) it only starts after about 1 second of cranking.” :wink_2:

Rayhennig, after the check valve replacement, please let us know if there’s any difference regarding that starting issue … and please let’s not get this thread too far off-topic … remember it’s about the ‘Lambda control (duty cycle) adjustment’. :wink_2:

… The other reason as you say is compensating for the different lean and enrichment characteristics of the EHA …
And refering to the ‘i.a.’ I used when I mentioned that, I’ll come back with more.

H.D.
 

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Correct. … Btw, you can certainly not be blamed for not having done your homework, Rob. :) H.D.
To the point of ridiculous excess no doubt, as my friend would say over a pint and fetid belch down the local tavern. :)

... But .. Gentlemen .. don’t forget what’s written in post 7: “When I start the car (cold/warm/hot) it only starts after about 1 second of cranking.” :wink_2: H.D.
I do not believe in replacing parts on hunches. It has the subtle effect of distorting the decision making from that point forward, and in this case by possibly giving false credence to the notion of loss of holding pressure. This despite no testing having been undertaken to verify this.

The KE baseline setting affects cold/warm/hot starting, and particularly the first 15 seconds of running.

I would advise not to change any parts until proper diagnostic tests have been done. I would start with the duty cycle.

...please let’s not get this thread too far off-topic … remember it’s about the ‘Lambda control (duty cycle) adjustment’. :wink_2:H.D.
I recall back when D-Jetronic was around, I read an article about tricks to get around the draconian control of the fuelling system. Apparently the Bosch guys used to unplug the air inlet temperature sensor 1 to improve the responsiveness of the engine. ;) If this was the Bosch way back then, it would be considered underhand nowadays... a bit like trying to fiddle emissions tests and getting found out!! :grin
 

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To the point of ridiculous excess no doubt, as my friend would say over a pint and fetid belch down the local tavern. :) ...
Lol

... I do not believe in replacing parts on hunches. ...
You’ll hardly find a stronger supporter of that opinion than me.

In a case like rayhennig’s I would not install new check valves .. I just mentioned them as one of the possible culprits and suggested to do fuel pressure test first, which would show whether there is a loss of holding pressure or not (post 8 and 10).
But he says he has them and he’ll install them (post 12) .. and I will not try to stop him from doing that.
With regard to the duty cycle he says he checked it and set it to a value he’s “very happy” with (post 9).

I’d say, let’s call it a day.

I will post more information regarding ‘KE-Grundeinstellung’. :wink_2:

H.D.
 
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