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Hi,

My 1990 420 missfires slightly after cold start at first traffic lights before engine has reached operating temperature. When warm it idles as smooth as possible. Starts as easy as possible too warm and cold. Is that normal or should I suspect injectors or something else?
I do not find anything out of spec anymore. It might be that fuel distributor has been rebuilt or replaced since lamda adjustment has been unplugged. Passes leak down test. Previous owner had been playing with adjustments in order to get the car running without any luck. Ignition coil was defect. Should I plug the lamda adjustment?
 

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Discussion Starter #62
Heikkif- When you say "plug the Lamda adjustment" I am assuming you are referring to covering the opening that accesses the screw adjustment. If so it will keep debris from entering tube, but it will not do anything to the way the engine operates. Your issue could be one of many ranging from fuel distributor, fuel injectors, ignition system, vacuum leaks etc. Before touching lambda adjustment (which would be last on my list) I would want to eliminate all potential issues that could be causing the problem.

One thing I have learned is that if someone takes the adjustment route to get a car to pass emissions and makes knowing or unknowing of the consequences it can be very difficult to restore it to factory settings AND you will still have the underlying issues just covered with a not very good band aid. Hope that helps, but that is where I would start my journey if I were you.


Hi,

My 1990 420 missfires slightly after cold start at first traffic lights before engine has reached operating temperature. When warm it idles as smooth as possible. Starts as easy as possible too warm and cold. Is that normal or should I suspect injectors or something else?
I do not find anything out of spec anymore. It might be that fuel distributor has been rebuilt or replaced since lamda adjustment has been unplugged. Passes leak down test. Previous owner had been playing with adjustments in order to get the car running without any luck. Ignition coil was defect. Should I plug the lamda adjustment?
 

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... When you say "plug the Lamda adjustment" I am assuming you are referring to covering the opening that accesses the screw adjustment. If so it will keep debris from entering tube, but it will not do anything to the way the engine operates. ...
It depends on how airtight the adjustment tower is. Pull a hose over it and try to blow air with your mouth through it. If it works, read post 48 of the thread I have mentioned so often in this thread … or forget the air blowing test and generally do what I suggetsed in that post. … ;)

... Your issue could be one of many ranging from fuel distributor, fuel injectors, ignition system, vacuum leaks etc. Before touching lambda adjustment (which would be last on my list) I would want to eliminate all potential issues that could be causing the problem. ...
^This is very well said, JR420. … :thumbsup:

... One thing I have learned is that if someone takes the adjustment route to get a car to pass emissions and makes knowing or unknowing of the consequences it can be very difficult to restore it to factory settings AND you will still have the underlying issues just covered with a not very good band aid. ...
^This is also very well said. … :thumbsup:

I‘d just like to add the following words (in blue):
“… it can be very difficult to restore it to factory settings ... or to professionally made settings that were indicated by duty cycle test results after part replacements or fuel type switches (ethanol / non-ethanol) ... AND you will still have the underlying issues just covered with a not very good band aid. …“


... I do not find anything out of spec anymore. It might be that fuel distributor has been rebuilt or replaced since lamda adjustment has been unplugged. Passes leak down test. Previous owner had been playing with adjustments in order to get the car running without any luck. ...
In a case where the Lambda adjustment screw has been tampered with, or you‘re not sure whether it has been tampered with, I basically recommend the two steps that I recommended in my last post.

step 1:
Check and, if necessary, fix everything that has an effect on fuel combustion … not only the injectors … also, for instance, all the other things I mentioned in this thread.

step 2:
Check and, if necessary, readjust the duty cycle via the Lambda adjustment screw.

If step 1 does not come into question, do at least a (proper) fuel pressure test (SP & LCP). ... If that is okay, continue with step 2.

H.D.
 

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Ok

But is it so that these engines should not misfire even slightly at any circumstances? Now it only does that before reaching operating temperature. Difficult to say if the difference is closed loop no miss fires and some in open loop. Fuel pressures are within specs and so is duty cycle as far as I understand. Next thing to check is the calibration of measuring flap potentiometer as now I got idle control working.
 

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... is it so that these engines should not misfire even slightly at any circumstances? ...
Yes, that‘s how it should be. … If that is not the case, there is a problem.

... Now it only does that before reaching operating temperature. Difficult to say if the difference is closed loop no miss fires and some in open loop. ...
By monitoring the “duty cycle“ you can tell if the misfires happen in open loop or in closed loop or in open & closed loop. … Plus, you might even see an error code appear. … :wink_2:

Check the duty cycle with “ignition on / engine off“ and then monitor it up from cold start until 2-3 minutes after the engine has reached full operating temperature. … If you like, report the readings and during what reading(s) the misfires happen. … Pay particular attention to fluctuations of the readings. See what I said about amplitude & frequency of the fluctuations under “Check procedures“ in post #2 in my Lambda control thread) !

BTW … in case of interest in significantly quicker & more comfortable CIS-E related diagnosing, have a look at this:
https://www.benzworld.org/forums/w126-s-se-sec-sel-sd/2906786-board-ke-jetronic-test-device.html
:wink

H.D.
 

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Discussion Starter #66
Finally after differential issues (still not entirely solved) summer vacations and you name it, I have car back. Short story long is there were major vacuum leaks between intake manifold and all 8 O-rings and lower intake manifold gasket were replaced, I was not able to detect those issues with carb cleaner spray method and had a chance to see the smoke coming out myself from the smoke test.

Shop was old school Mercedes trained 26 years ago on Bosch fuel injection and hadn't heard yet of EHA being adjusted due to that being a "taboo" adjustment.. Car is much improved, but still a rough idle, they used exhaust gas analyzer to test hyrdro-carbons and determined cylinders 1 and 5 did not change reading like others did when disconnecting spark plug wires indicating a lean burn situation. They also pulled off fuel lines on fuel distributor and found that cylinders 1 and 5 were slower then others on fuel accumulation.

Question - and I appreciate all responses, if previous owner changed EHA setting would/could this possibly impact air/fuel ratio for just these two cylinders or would that impact air/fuel ratio for all equally? Fuel Distributor rebuild did include as best I could tell a bench test that passed expected measures in all ports and I'm at a loss on trouble shooting to do from here.
 

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Out of curiosity where was the fuel distributor rebuilt? I have heard there are companies who know what they are doing and then some who should not touch those. If fuel is not distributed evenly after rebuilt could be the second case.
 

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Discussion Starter #69
Had it rebuilt from a guy on Ebay. Based on reviews it seems he has been doing a good job.

Looks like I will need to send it back.
 

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... there were major vacuum leaks between intake manifold and all 8 O-rings ...
In post 40 of http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/2720049-ke-jetronic-lambda-control-duty-cycle.html I said:

“An intake vacuum leak causes low O2 sensor voltage. The ECU immediately reacts by sending higher current (in positive direction) through the EHA’s coil in order to increase the amount of injected fuel as an attempt to compensate for the vacuum leak and raise the O2 sensor voltage again, which works if the leak is not too big and the Lambda enriching limit via EHA control is not reached or exceeded. ... In that case this higher EHA current is represented by a duty cycle fluctuating in a higher range. It can, of course, be lowered again by raising the position of the FD‘s control plunger in relation to the AFM plate’s position via Lambda adjustment screw … which most DIYers would probably do … with the consequence that during each warm-up phase (before Lambda control is active) the engine will suffer from way too rich a/f mixture. … It would be much better to leave the adjustment screw alone and lower the duty cycle again by fixing the vacuum leak, wouldn’t it !?

Seems like a PO did the opposite with your car. He let the vacuum leaks be vacuum leaks and just lowered the duty cycle via the adjustment screw. … :rolleyes:

... Shop was old school Mercedes trained 26 years ago on Bosch fuel injection and hadn't heard yet of EHA being adjusted due to that being a "taboo" adjustment. ...
See what I said at the end of post 60 in the above mentioned thread:

“… reminds me to what one of the Bosch engineers who designed the KE-Jetronic once said to me in the 1980‘s. He said that it will be the least understood gasoline injection system, no matter how many will claim to understand it … and that they better hide the EHA adjustment screw … and that a difficult to remove plug in the Lambda adjustment tower is an absolute must.“

... if previous owner changed EHA setting would/could this possibly impact air/fuel ratio for just these two cylinders or would that impact air/fuel ratio for all equally? ...
If there is no problem with the FD or the injectors, the latter would be the case. In case of specific problems with the FD or the injectors, the former could be the case.

... Fuel Distributor rebuild did include as best I could tell a bench test that passed expected measures ...
See what I said in post 56 (of this thread) !

I suggest to check the ignition system too … best with an oscilloscope.


P.S.:
After the forum design change the formatting of my threads has been changed and complete posts of mine in them have disappeared. :confused: ... Due to worries that this may not be the last time that this happened I prefer to further assist in troubleshooting issues … and provide detailed CIS-E related info & advice in general … via private email instead of posts in threads. PM‘s are also not practical, because there is, unfortunately, still a problem with BW's email notifications.

Best wishes!

H.D.
 

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Discussion Starter #72
Thanks HD - just to confirm below an EHA (have no idea if mine was adjusted) could indeed cause one or two cylinders to run lean also experience a rough idle?

I have not yet trouble shoot the FD by removing lines and visually inspecting flow. Rebuilder is suggesting turning retaining collar by a quarter turn at the metering pin clockwise to increase fuel flow earlier. States it is currently set at factory specs, but that may not accommodate wear in the throttle plate. In addition rebuilder showed/states that bench test flow of FD showed all within 15% of each other.

New fuel filter was installed just prior to FD rebuild so it shouldn't be a debris related issue.

Yes - previous owner was without a doubt compensating for a major vacuum leak. Have also replaced wires, cap, rotor, new non-resistor plugs.


JR420 said:
... if previous owner changed EHA setting would/could this possibly impact air/fuel ratio for just these two cylinders or would that impact air/fuel ratio for all equally? ...
If there is no problem with the FD or the injectors, the latter
would
be the case. In case of specific problems with the FD or the injectors, the former
could
be the case.
 

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Thanks HD - just to confirm below an EHA (have no idea if mine was adjusted) could indeed cause one or two cylinders to run lean also experience a rough idle? ...
In combination with specific problems with the FD or the injectors: Yes.

... Rebuilder is suggesting turning retaining collar by a quarter turn at the metering pin clockwise to increase fuel flow earlier. States it is currently set at factory specs, but that may not accommodate wear in the throttle plate. In addition rebuilder showed/states that bench test flow of FD showed all within 15% of each other.
I have refurbished & recalibrated a lot of CIS-E FD‘s over the years and I warmly recommend to have your FD‘s calibration checked and, if necessary, corrected by someone else who really knows how to do that. Not only should the maximum volume flow difference between all injector ports (without injectors connected) be a lot smaller than 15%, but the absolute volume flow should, under specific test conditions, be within a specific range too !!

I said a few things regarding FD calibration also in https://www.benzworld.org/forums/w126-s-se-sec-sel-sd/3019718-cis-fuel-distributor-initial-settings.html#post17722752 ... and in another thread that I don't remember right now.


P.S.:
Please remember … with the forum problems I already had experienced before the forum design was changed and with the new problems (partly mentioned in my last post) I prefer not to further post in forum threads, untill these problems are fixed. In case of further interest in my assistance you & other readers are welcome to send me a PM with your/their private email(s). :)

I would actually like to share a lot more detailed info & advice … especially about the commonly not really understood KE-Jetronic … but I‘d like to do that in a forum whose technical quality reaches to a level that is more appropriate for a place where help seeking owners of classic MB‘s can find professional information & advice.

H.D.
 

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JR420: Some of your symptoms sound similiar to mine after my FD was rebuilt(same guy)/new injects/injector seals put in. I seem to recall watching the gas fill up my ports and noticing that whichever port is at about the 10/11pm position (facing windshield from front bumper) and the 7 or 9pm position...those two filled up slower than others. (Apologies for not knowing which two cylinders those ports represent). My initial test drive was almost undriveable (fuel starvation big time) so I think your condition starts off better than mine. As you know, I resolved my driveability and idle issues by a lot of various adjustments to the EHA and tower screws. Exam of the spark plugs after about 400 or so miles of driving showed all plugs looked almost identical in condition(I was always told years ago, that one of the best indicators of how an engine is running is by condition of spark plugs) and appeared to show a balanced mixture (not too lean, not too rich). Since your tower screw is already been adjusted, and it appears your EHA has been adjusted as well, seems to be not much risk in trying a couple of minor turns on one or the other and making careful note of your pre-post adjustment positions. Worst case, you return the adjustment to where they were before you touched them.

One day when im not traveling and can make time, I'll get that smoke test done and will also check other areas in order to get things adjusted the right way/properly. But for now, I'm comfortable with the results.



And its refreshing to be able to know that she fires up first time each time, no stuttering/stumbling after the start, and doesnt shut off at the first stop sign down the block after the first start of the day.
 

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H. D. we must recover them. Is it possible to get details?
Ianrandom, I sent you a PM regarding ^this.

Since I haven‘t heard back from you … and in case that after the forum design change there is also a problem with private messaging (now called “conversations“) … I reply via this post.

I’ll have to see if & what backups I can find. … What should definitely be recovered is my disappeared post #40 (a continuation of post #39) in my “KE-Jetronic Lambda control (duty cycle) adjustment” thread (https://www.benzworld.org/threads/ke-jetronic-lambda-control-duty-cycle-adjustment.2720049/). That was/is one of the most important posts in that thread. I refer to that post in many other threads.
The subsequent posts should get their original post numbers back too, because I refer to these post numbers in other threads too.

If I can not find backups of posts that have disappeared after the forum design change, is their any hope that they can be found at Benzworld and recovered (reintegrated at their original positions) ??

H.D.
 

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Discussion Starter #76
Thanks all for thoughts on this. I just began some diagnosis. Have not adjusted EHA yet, but I did unplug it at operating temp and it idles absolutely smooth as can be. Misses on acceleration, but not much more than with EHA plugged in. Of course check engine light then turned on due to EHA being unplugged.

After plugging back in rough idle returns to rough state immediately. . . Guessing it's highly likely previous owner adjusted EHA at this point. If Fuel Distributor was faulty I would think unplugging EHA would not smooth out engine as cylinders 1 and 5 would still have been starving for fuel.
 

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As two cylinders are misfiring constantly or just running lean exhaust has oxygen left in it. While EHA is connected computer is able to increase fuel to burn all O2 from those misfiring cylinders too. Too much fuel for the rest of the cylinders then causes the engine to idle poorly. Basic settings of lamda tower and EHA being correct engine idles better in open loop(= EHA disconnected) than in closed loop . This is how I would explain it to myself. If fuel distributor is not delivering equally to all cylinders it is no use trying to adjust the rest of the system.
 
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