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'91 Merc 190E 2.3
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Discussion Starter #1 (Edited)
My vehicle has failed the E-Test. How do i properly test my 1991 Mercedes 190E 2.3's O2 Sensor to see if it is in working status?

Perhaps i did not perform my last test correctly but here's what i did:

(( The multimeter RED & BLACK ends -- RED connected to female coax & BLACK connected to frame of car ))





The RESULTS:

I set the multimeter to the left on the V (with a straight line + dash) and 2000m:



I turned on the car (Automatic), placed in NEUTRAL, and let it sit for a couple minutes. The reading on the multimeter for 2000 m = 115. When i gave it lots of gas the reading spiked to 950 and remained fixed. When i let off the gas it returned to 115. Again with ample gas it peaked at 950.

I switched the multimeter dial to 200 (with the line beneath it). The reading for 200 m = 0.1. With gas it peaked at 0.9 and remained fixed. No gas it returned to 0.1.

Did i perform the O2 Sensor test with my multimeter correctly? Is my O2 Sensor working correctly? Do i need to remove it for a cleaning / replacement?

Thanks
 

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87 300D 5 speed
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5,523 Posts
A new generic 3 wire O2 sensor can be had for $40. It usually pays for itself in better fuel economy. My car failed smog in California (same ASM 5015 and 2525 as you have in Canada) because of high HC but my NO was very high as well, bearly passing. Here's the before and after replacing the O2 sensor.
http://img.photobucket.com/albums/v242/tjts2/Green Mercedes/003-5.jpg?t=1290095144

My car has 177k miles with the original cat.
 

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'91 Merc 190E 2.3
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232 Posts
Discussion Starter #3
A new generic 3 wire O2 sensor can be had for $40. It usually pays for itself in better fuel economy. My car failed smog in California (same ASM 5015 and 2525 as you have in Canada) because of high HC but my NO was very high as well, bearly passing. Here's the before and after replacing the O2 sensor.
http://img.photobucket.com/albums/v242/tjts2/Green Mercedes/003-5.jpg?t=1290095144

My car has 177k miles with the original cat.

Where do u purchase your O2 Sensor? Here in Canada PartSource, NAPA, and the dealer sell new sensors for no less than $180 for my Merc, much more than the $80 i paid for the new Cat Conv.
 

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87 300D 5 speed
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5,523 Posts
That $80 cat will pass smog precisely once. Thats why California banned those a few years ago. A real cat is closer to $500-$1000.

Any 3 wire O2 sensor works. The only difference between any of them is the plug.
3 wire O2 sensor - Google Search

I got mine at NAPA. Ask for a generic Bosch 3 wire O2 sensor. If the guy at the parts counters asks what car you have tell him it doesn't matter.
 

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'87 190E 2.6
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186 Posts

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1991 190e 2.3, 1997 C280, 1981 300D Euro (Sold), 1998 BMW 328i
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104 Posts
The O2 sensor should read about .5 volts when the engine is running normally. This, I believe corresponds to a 14.7 air to fuel mixture. A higher voltage indicates a richer mixture and a lower voltage indicates a leaner mixture. I would think that your sensor is working if the voltage output changes with throttle changes. In my state they check the emissions at around 2000 rpm under load as if the car was going down the highway.
It could be a number of things causing your problem but I would check the Ignition System first. Good Luck
 
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