89 300CE running rich/hesitation/Duty Cycle stuck at 82%

[visal911]

Hi guys,

This is my first post at PeachParts but some of you might know me from BW. Benzworld.org - Mercedes-Benz Discussion Forum - View Profile: visal911

Anyway as per title I'm having a few problems with my M103 powered 1989 300CE running rich and some lack of power.

This started being very noticeable after a new Spark plug, Distributor Cap and rotor change. I used Genuine Bosch parts and proper NGK non resistor plugs.

After Driving around for a bit like this I noticed that the car needed more push in the pedal to go and the economy gauge was in the middle at 60kmph when it usually was in the left hand corner. The new plugs were a bit dark after about 200kms. I will post pictures tomorrow when its day light.

So I tested the Duty cycle with a Multimeter and it was at 82% and 11.11V ~ according to what I was reading, higher V means That its running rich and the 82% is the proper OFF Mercedes Duty cycle.

I gave the screw a couple of tiny turns and a couple of big ones and waited for 10-20 seconds but nothing happened! The Reading did not go up OR down. It was like something else was enriching the mixture!!!

The car reads a 50% when started up and 50%~ at WOT.

Tested for Vacuum with a mittyVac - 15(hg?).

After reading lots of posts and other CIS material I have come to the conclusion that my O2 sensor has gone bad and is giving a wrong reading. Check engine light is not ON though. It flickered on and off a couple of months ago but haven't come on since. Car stinks of unburnt gas out of the exhaust.

What do you guys think? I don't want to throw parts at the car without knowing for sure and I cant really test the O2 or any other sensors because of the cold and I don't have a garage to work in.

Reasons for this happening after the tune up? City Mpg is pretty bad. I still get 10L/100kms on the highway.

What I have replaced

Rotor
Distributor Cap
Spark plugs
Fuel/Air filter within 30,000kms
EHA
Always running shell 91 without ethanol

Thanks a lot,
V

Hope to get to know people here and share my knowledge and experiences about these great cars.