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'91 300CE M104 and '86 560SL
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237 Posts
Discussion Starter #1
I have had ongoing problems with declining gas mileage, cold and warm starts etc. (Question has posted on another forum), Tested O2 sensor following procedure outlined here and my sensor does NOT cycle between .1 and .9v. It started to - after the car warmed up - but then following a click in the motor area the voltage went to 1.04v and stayed there. So, I checked the duty cycle and it went from 70% KOEO to 50% at cold idle to 98-99% when warmed up - and it stays there. Sounds like the car is running rich and staying in open loop...???

Question: does the fact that the O2 sensor is not cycling automatically mean a bad O2 sensor, or is there some other issue that is causing the O2 sensor to not cycle? Is the fact that the O2 sensor is doing this the reason the duty cycle is not cycling either?? I'm just trying to figure out the proper sequence here...This is a relatively new Bosch direct replacement - within the past 2 years and 15K miles...

Any help? Thanks.

Ryan
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,745 Posts
Ryan,

The O2 sensor is a service item and should be replaced approx every 60K miles IIRC. When was your's changed last?

Jayare
 

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Registered
'91 300CE M104 and '86 560SL
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237 Posts
Discussion Starter #3
2 years ago...approximately 15-20K miles. I used a direct fit Bosch...

ryan
 

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92 400E, 95 S500,91 300TE practically stole it, 97 V10 Ford E350 to tow them home from time to time
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4,492 Posts
If you have the wrong plugs installed, one may have worked loose. Guess how I know...
 

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Registered
'91 300CE M104 and '86 560SL
Joined
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237 Posts
Discussion Starter #5
They are the right plugs - I'm trying to pull them to take a look, but I can't get the wires off!
 
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