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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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7,970 Posts
Discussion Starter · #1 · (Edited)
I spend a lot more time on my 190K mile 560SL than on my 47K mile 380SL.
I'm now quite versed, more likely dangerous, about the KE-Jetronic fuel injection on the 560SL than I am with the older K-Jetronic fuel injection on the 380SL. So, now I am wanting to learn more about K-Jectronic.

I use an Oscilloscope because I already have several but don't have a Duty Cycle Voltmeter.
If anyone can recommend a reasonably priced one I can get off Ebay or Amazon I would appreciate that.

Anyway here is a comparison of the wave forms on pin 3 of the diagnostic ports.

560SL:
ZZZ_2021_05-04_003.jpg


380SL:
ZZZ_2021_05-04_001.jpg

Both cars are running extremely well.
My Oscilloscope is on the 2ms scale and each cycle occupies 7.5 divisions - so its 67hz by my scope.
BUT, I read that its 100hz, so it could be my scope or I have my time base controls set in an un-calibrated mode. These are older photos when I wasn't concerned about the time base.

Delete that ... its 100hz. I updated the photo with another photo where the Oscilloscope was in a calibrated mode.

Oh well, you can see for the 560SL we have a pretty nice square wave depicting a pretty good Air to Fuel ratio.
The 380SL waveform is a bit more complex. I did not realize when I took these photos that I had delayed sweep going on - so ignore the intensity on the start of the waveform.

So, how does one adjust Air-Fuel ratio on the 380SL's K-Jetronic and what are we looking for for an optimal setting. My 380SL mixture adjustment still has the factory seal that I have not drilled out ... yet :)
 

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R107 300 SL, Year 1986 and C124 300CE-24 Year 1990
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165 Posts
Hi Carl,

I bought this multimeter a few years ago, € 99. All measurements can be carried out with it.
Regards Marcel
DSC01954_Bildgröße ändern.JPG
2690283
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1985 380 SL
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I checked mine on my 1985 380, attahed is a screenshot of the scope (I use a PC based scope). It shows just over 50% duty. For the 1985 the spec is that the readings are supposed to be the same at 2500 rpm and at idle, as best I can tell they are. Earler cars show the spec to be 50% as a target, test values 40 to 60% are acceptable. The adjuster on my car has not been touched either.
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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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7,970 Posts
Discussion Starter · #4 ·
What frequency are you reading?
I went and rechecked with my Oscilloscope this morning and I find it to be 66Hz for K-Jetronic, and 100Hz for KE-Jetronic.

On 380SL: 3 divisions on 5ms scale = 1/15ms = 66hz:

3 x 5ms = 66hz.jpg
 
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