Yes, that is what I intended. After installing it, I was getting a continuous o2 sensor reading of 0.84~0.85V which meant the mixture was overly rich.

 

Hi, my 1989 300TE was running rough and had no power once it reached the running temperature of 80. After reading another thread here I went looking for the oxygen sensor and found that it was missing. The last owner must have replaced the exhaust system removing the sensor. I found the unconnected wires under the right hand floor carpet.

shdoug your solution works. After adjusting the mixture screw slightly leaner the car ran smooth again with a lot more power, however the idle is now a little rough but I can live with that for now.

I have located a dude who is wrecking a 300TE for parts so I have sent a message asking whether he will sell the exhaust system to me. I feel that this would be the best way to add the sensor and also fix a damaged muffler.

I am also looking at replacing the disruptor and rotor with new ones for about $200 New Zealand dollars because the current ones are wearing out.

Thank you for all the good information here. They maybe old posts but they are still helping owners like me work stuff out.

 

You don't really need to buy part of the original exhaust system to be able to fit the o2 sensor. Just have the muffler shop open a small hole and then over it braze on a nut in the area of the exhaust pipe where the sensor normally goes and that will fit the thread on the sensor. That is what I did and it works perfectly. Just make sure the hole through the nut is clear all the way into the exhaust pipe. The o2 sensor thread size is 18MM (M18 x 1.5 thread). You can also buy a o2 sensor "bung" from many online dealers, but it will cost more and basically will do the same job as the plain nut I used.

 

Hey Alex! This thread is a bit old but it turns out I'm in the same boat. Went looking for the O2 sensor while checking duty cycle and found it missing and no plugged holes visible on the exhaust either, so the exhaust was probably replaced also. Voltage starts at 7.5v then holds at 5.6v steady after warmup.

Now the car feels pretty slow in low gears. Cold starts take longer cranks. Warm starts are half a crank, so perfect. And I just changed my oil a couple of days ago, which in 2 days has gotten very watery (no signs of actual water).

Apart from the above, there are no warning lights, the car runs decently and doesn't stall while driving or anything.

So my question is, are you faring better with the O2 or were you better off without?

 

Hey there.

That was done a good while ago. I remember noticing that afterwards the mixture was running much closer to optimum, fuel economy improved somewhat (not that my enthusiastic driving style helps much with that anyway), and of course finally got rid of the Check Engine light for good. With the feedback from the o2 sensor what happens is that the Bosch KE-Jetronic injection dynamically optimizes the mixture, its a closed loop system which will bump the mixture all the way rich in the absence of the expected input voltage from the sensor as it is interpreted as a lean condition and it will try to compensate by adding some extra fuel. In any case by itself the KE-J system under normal circumstances will not stray too far away from the ideal because in itself it is mechanically so accurate, like a fine watch, that even without the electronic feedback it will still allow the car to run very close to optimum and most people won't even notice any difference in the driving behavior other than some tailpipe soot and a tank lasting somewhat less than expected. And definitively the Check Engine light coming on, unless of course someone did remove the bulb. The electronic input from the sensor just allows the KE-J to further dynamically fine tune the mixture that much closer to optimum under all driving conditions. Another obvious advantage of this system is that even with the electronics part failing completely it will still keep the car driveable and never ever leave you stranded.Try doing that nowadays with a "modern" car that heavily relies on the electronics to adjust mixture.

I really only started looking into the missing o2 sensor because my chromed AMG tail pipes where always showing a bit of black soot on the inside and around the rim of the openings. When I rubbed a finger in there it would come out pretty black, obviously meaning combustion was too rich. In other words just wasted unburned fuel but still performance wise the car was seemingly always perfect. After adding the sensor I remember that there was also an adjustment to be made to dial in the sensor's output to fall into the correct range so it would be interpreted and acted upon correctly also taking into consideration if the engine temperature was cold or hot, etc. Also remember that at some point also checked and adjusted the upper and lower chambers of the fuel distributor to the correct vacuum differential which also affects mixture but requires having the appropriate gauges handy, and knowing the correct values and procedure to make that adjustment. All the info is in the W124 service manual available online for free download at a couple of sites out there. If you don't have it already, just search for "Mercedes W124 Service Repair Manual" and you should be able to find it. I also recall it could be purchased cheaply on a CD off ebay. Another recommended book to have is the "Mercedes-Benz E-Class (W124) Owner's Bible 1986-1995".

Hope that helps, and good luck.
Alex