1979 450SL warm up regulator adjustment?

[Richard Wooldridge]

Hello all,
My 450SL was idling rich after warmup, and after much reading I decided that a possiblity could be the warm up regulator. (The symptom observed was that I could push down on the airflow sensor plate and correct the overrich condition, but couldn't adjust it lean enough with the idle mix adjusting screw.)I removed it from the engine, unscrewed all the screws and nuts holding it together, and very carefully removed the bottom plate. I found a diaphram that is controlled by manifold vacuum, with an adjustment screw in the middle, that pushes against a spring which in turn pushes against the valve plate that controls the line pressure for the injector control piston. My thought was that I had too little pressure, so I screwed the adjustment in about .050. I then reassembled the warm up regulator, reinstalled it, and after readjusting the airflow sensor plate's idle mix adjusting screw it idles very nicely now. (Before, I couldn't get it to idle lean enough regardless of the adjustment.) This year CIS has no feedback, no O2 sensor. I did check out the heating element, it has 24 ohms resistance, seems good. When I took the unit apart, the bimetallic strip was still up away from the springs. (Hot condition)

My question to the learned folks here on the forum is: Did I do the right thing? I know this unit was calibrated carefully around 26 years ago, but I'm thinking that the springs might have weakened a bit as they aged. I'm thinking I should order out a CIS-K pressure gage set, I see them advertised for around 60 - 80 on a few websites. What should I see on the high pressure side of the warm up regulator valve, cold and hot? Would it be worthwhile to consider installing the pieces to add lambda control to the engine?
I am a newbie to the intricacies of the CIS-K setup. What is the purpose of the unit between the warm up regulator and the injection pump? It looks a little like a pressure regulator, but the vacuum control line is connected to the air cleaner on my car, so I don't think it could be regulating much. (update: after more reading I found the answer to this question, it is a pressure damper, and was removed in 1981 when they made the tecalan element in the control pressure line longer.)
Thanks for any illuminating answers you have!

[oxymoron]

Try www.w116.org for adjusting K-jet and hot/cold pressure testing specs.
There's a section at that website for the manuals.

There's a Charles Probst book on Bosch FI that's always on e-bay.

Sounds like you are on the right track, but CIS is all about pressure and volumes and without gauges hooked up, you are just guessing.

I saw in another thread that you have the Unwired tools' servo replacement. I guess you are also aware that they make a warm up regulator replacement as well.

[Richard Wooldridge]

Thanks, I appreciate the links... I saw the unit that Unwired Tools sells, actually I talked to Steve there, and he told me about pushing on the airflow plate to see if it would cause the mix to lean. (He said if you push on the plate and it leans out, then the warmup regulator isn't working properly, not enough pressure.) I'm somewhat interested in their unit, but it's pretty spendy. I would go for the adjustable one with the gage, I think. I will check out the book you mentioned, also the link.

[wbain5280]

Originally Posted by Richard Wooldridge

__________________
Richard Wooldridge
'82 300D 4.3L V6/T700R4 conversion
'79 450SL, digital servo update
'75 280C

Richard, what's this 'digital servo update'?

[Richard Wooldridge]

Hi Wbain 5280,
The digital servo update is a nifty although expensive device that is sold by Unwired Tools (http://www.unwiredtools.com) to replace a troublesome climate control control unit used from around 1976 - 1981 in some of the Mercedes vehicles. It was developed by Chrysler Corporation for the 1971 Chrysler Imperial, and slightly modified and adapted by Mercedes, they called it the ACII climate control system. The control unit combined blower speed control, vacuum pod control, and heater valve control all in one unit that was driven by a small electric motor which was operated by a differential amplifier. Unfortunately, the heater valve tended to bind up and/or leak, causing the little electric motor to keep trying to run, even with the key switch turned off, which would run down the battery. Also the 9 or so vacuum lines going into the unit would start leaking at the connector over time, killing the whole operation. If you don't have one of the cars with the ACII system installed be glad! Happily, the digital servo update takes care of all the problems except for the vacuum leaks, which can still occur, usually due to a leaky vacuum pod after 25 years of service. I hope that explanation clears it up for you!