Just when I thought this was all making sense, now I get thrown a curve. My 1990 300te has a 103.983 engine according to all documentation that I have ever seen. While trying to troubleshoot the duty cycle issue for a California car, I see that I have parts that are specified for a 104 engine.

Case in point; the pushbutton LED for diagnosis for a CA car as of 1988, an 8-pin version, is replaced by a 16-pin version on engines 104, 119. I have the 16-pin version.

Case in point; the KE Control Unit (N3) has a 25-pin configuration that is specified for engines 102, 103, 116, 117. I have the 55-pin version that is specified for engines 104, 119.

The reason that I have not been able to get my LED into the "continuous on" mode is because you can't do so with the 55-pin connector. It has a separate wire to contact 30 that supplies the on/off ratio (lambda test signal).

My duty cycle reading was 35% (rich). All of the write-ups I have seen say a CCW turn is needed to lean the fuel ratio back up to a target of 45%. When I tried to turn CCW, the ratio went lower and lower. I was able to get my ratio corrected to 45% by turning the tower screw CW by about 5 degrees from its' original position.

I have very few pages of wiring diagrams and test procedures from my WIS that apply to fuel management for this type of configuration. Do I need to now start looking at specs for 104 engines to figure out how to properly tune my car? When did MB start indroducing 104 components into the 103 engines? Is this just a California thing?

You obviously have a 103 motor. The distinguishing characteristic of a 104 motor is dual overhead cams and 4 valves per cylinder. It came out in 1990 in the 300CE and the 300SL. MB chassis and motors share parts but typically get the part number from their first application (e.g. 104 motor, 129 chassis, etc.) but they are by no means unique to that application. A 16 pin connector is quite common on later 103 motors. The documentation is not always perfect about where a part may have been used.

Here is a pic of my sons 1988 300TE engine bay... 103 I believe.
Ignore the red arrows, they are from a previous question.

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2009 Mercedes ML320 Bluetec

Thanks Merkey,

I was being a little tounge-in-cheek when I asked which engine I had. It was just the frustration of doing all the research on how to troubleshoot and do a repair, and then finding something different when I opened the hood.

Having to turn the idle mixture screw CW instead of CCW like everybody says to lean the mixture was just the kicker.

Speaking of opening the hood, the only differences I see in our engines are your lack of an EGR valve, the stamped thermostat housing instead of my cast piece, and the hideous orange Phram oil filter trying to hide in the back.