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Discussion Starter #21
Myndex, you are coming to the GTG on weekend of april 9th. Any chance you would be willing to give the guys a demo on what you have proven to be an excellent way to check our lambda system. Maybe bring along a short list of items for us to get. I will offer my 280sl as a demo auto.

Dennis
Yes, indeed I am planning on attending - I'll bring my oscilloscope, duty cycle meter, etc.

For your 280sl - as that is a euro model it would not have the Bosch lambda ECU, but if grey market could have the Johnson aftermarket ECU.
 

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My 84 is a ROTW, imported from Spain............... :)

When I first purchased the car I had no clue about Mercedes, the differences between a 380 or 560, let alone the differences between US/ ROTW.................. I looked for a frequency valve and smog equipment for months.... :)

Then I found Benzworld......

RC
 

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High Idle / Max Rich Problem Solved

So it goes max rich after warmup?

Okay, have you adjusted the mixture at the fuel distributor, per sections two and three of the first post in this thread, with the engine at full operating temperature?

50% solid means the O2 sensor is not hot yet. Once it is hot, then it will try to adjust mixture. If the duty cycle is pegged at 95%, then richen the mixture (clockwise). You can start with ¼ turn clockwise.

Note that when the O2 sensor is cold, the mixture should read 50% (or 60% if the engine oil temp is cold) REGARDLESS of how the mixture screw is adjusted.

Once engine and sensor are at operating temp, only then make adjustments to the mixture screw.
Andy thanks again. I was able to get the ECM to control the mixture down to the normal range even at high idle using the mixture set screw. That is when I realized that the problem was not in the mixture but in the idle control. I gained access to my idle controller, nested against the heater behind the glove box to the left of the switchover valves, and found that by moving the plug the idle would change. So I removed the PC board and re-touched most of the soldered joints, reassembled, only to find that the high idle was still there, surging whenever I moved the plug. I removed the cover from the idle controller plug and using a pair of needle nose closed up the gaps in all of the sockets. That stopped the surges but the idle was still high. I decided to remove the idle valve with the intention on cleaning it and, as soon as I removed the air filter box, found a disconnected vacuum line. I reconnected it and the idle immediately went back to normal. The only thing I had to do was to re-set the mixture. I love it when this beast purrs like a kitty! Thanks for all your guidance.


 

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Dragonflyer, you should come to the GTG next weekend in belair. You are not far away from meeting a bunch if great mercedes guys
Who are on the forum here. Read the first sticky and add your name to the roll call

Dennis
 

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Dragonflyer, you should come to the GTG next weekend in belair. You are not far away from meeting a bunch if great mercedes guys
Who are on the forum here. Read the first sticky and add your name to the roll call

Dennis
Thanks Dennis, I usually work on the weekends but I shall do my best to try & make it. I think if I offer my wife to drop her off at the Neiman Marcus on Wilshire she'll give me a day off :grin
 

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You will get a lot out of the GTG. We are headed to the classic center in irvine on friday with our cars. Tom hanson has
Been alerted that we will be showing up for a tour of the facility.
Sat is a work on cars day. And sunday is a classic car drive up the PCh.

Just get on your knees and do a bit of begging or give her a credit card to go shopping
 

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Wouldn't you be more likely to get Pex's attention if you mentioned his name like this? @Pex
I refuse to do that just as I refuse to send hearts to other members. The number symbol has been bastardized to mean hash browns or something like that. BAH
 

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Discussion Starter #34
Andy thanks again. I was able to get the ECM to control the mixture down to the normal range even at high idle using the mixture set screw. That is when I realized that the problem was not in the mixture but in the idle control.
--snip--
Cool, glad you got it sorted out.

The way the idle control is routed mixture won't be affected if the idle controller is set wrong – however depending on where a vacuum leak is, it may affect the overall mixture.

K-jet and KE-jet is very sensitive to vacuum leaks.

And yea,when working right, these engines purr nice...!
 

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Bump

On my 1984 380sl, the advice above to swap the negative lead to pin 17 and red for pin 16 did not work for me.

I noted some differences on my ECU as well as with the part numbers.

For starters, putting the negative pin on pin 17 and positive on pin 16 resulted in no duty cycle. As in 0%. Swapping was the same result.

Only putting the negative probe on pin 17 resulted in a number that would operate inversely to what the actual settings are (counterclockwise - lean; clockwise - rich).

When I put the positive prob on pin 17, I was able to get the A/F mixture to respond to counter clockwise for lean and vice versa correctly.

Strangely, I could only read the duty cycle when only one probe was touching pin 17 for either negative or positive leads.

So in short: if you are working on at least a 1984-1985 380sl and are attempting to set your A/F mixture, make sure that you only put the positive probe on pin 17 and let the negative probe lay to the side.

Per the FSM, you also need block off the ports to the charcoal canister that lead to the engine AND turn off air conditioning.

For the 1984-85 model years, you're supposed to rev the engine to 2500 RPM and take the duty cycle reading then let it fall back to idle then check again. The value should not deviate more than 10% from each reading. In all reality, it should rest at around 50 %(+/- 2). At 2500 rpm, the duty cycle number should move between 45-55%.

Hope this helps those who are working with model later than Myndex's!
 

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Now, though all of this until this last sentence, I’ve avoided the term “duty cycle” - you’d see though (watch the video) that there is a duty cycle of the amount of the wave form that is PWM, and the amount that isn’t. Unfortunately, you can’t read this directly using a regular duty-cycle meter - you need an oscilloscope, OR the Bosch tool that is designed specifically for converting the PWM portion TO a duty cycle for diagnosis.

NOTE: I am looking into some methods of adjustment that could allow the use of a regular duty cycle or dwell meter, but have yet to asses them for accuracy.


This concludes the overview and adjustment of 1980 thru 1985 K-Jetronic WITH Lambda fuel injection systems. I hope you found this helpful.

Cheers,

Andy
Very interesting subject. I need to buy an oscilloscope to do this but know nothing about them. Would this one be suitable or any other tip on which one to buy?

https://www.banggood.com/Upgraded-MUSTOOL-MDS8207-Intelligent-2-in-1Digital-40MHz-200MspsS-Oscilloscope-6000Counts-True-RMS-Multimeter-p-1496130.html?akmClientCountry=SE&rmmds=cart_middle_products&cur_warehouse=CN
 

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Very interesting subject. I need to buy an oscilloscope to do this but know nothing about them. Would this one be suitable or any other tip on which one to buy?

https://www.banggood.com/Upgraded-MUSTOOL-MDS8207-Intelligent-2-in-1Digital-40MHz-200MspsS-Oscilloscope-6000Counts-True-RMS-Multimeter-p-1496130.html?akmClientCountry=SE&rmmds=cart_middle_products&cur_warehouse=CN
Yes, that tool looks perfect for what you will be using it for.

I should have spent money on that bad boy instead of my duty cycle meter. That's far more useful!
 

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Yes, that tool looks perfect for what you will be using it for.

I should have spent money on that bad boy instead of my duty cycle meter. That's far more useful!
So, I ordered it. One question though, where would i connect the oscilloscope to the 380SL to be able to adjust the mixture?
 

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So, I ordered it. One question though, where would i connect the oscilloscope to the 380SL to be able to adjust the mixture?
Since you have the oscilloscope, stick the probes into the X11 diagnostic port that is in the engine bay. Pins 2 (+) and 3 (-). I think that's the correct polarity.

Open your hood and look to where the brake booster is on the driver's side (US). There will be a small black circular object. Unscrew him, stick in the probes, and you're in the money!

It's much easier to use this method than the one I have to do since I only have a duty cycle meter.
 

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Finally Received my oscilloscope yesterday so it will be interesting to see how it looks when i hook it up.
Another thing, my 35 year old timing light isn't so bright any more and my old analogue revcounter doesn't work on any of my cars including the 380SL so i wan't to buy new ones. Any tip on a good timing light and revcounter?
 
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