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90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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236 Posts
Discussion Starter #1
My car has just this slight miss when warm and idling. I think this stumble is pronounced when at operating temperature. So I am guessing this is happening when engine goes into closed loop operation.

I was going to replace the O2 sensors.

Questions are:
How many o2 sensors are uses in the car
What are the part numbers
What is the best brand (apart from of course, Mercedes OE) to buy. Push comes to shove, and if prices are reasonable, I may go for OE too. But only if price is reasonable.
 

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1991 560sec. 1969 280SL
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1,077 Posts
i would test the O2 sensor first. Its connection is under the passenger front carpet to the left. You need to disconnect the single black wire for reading below 1 volt. Engine at operating temp. reading should around 0.4 to 0.8 volts at idle.
also check the O2 heater wires for power and ground at cold start up.
 

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Registered
90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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236 Posts
Discussion Starter #3
Thanks Gogi. I appreciate your reply and I will do that. I know you are one of the seasoned members of this forum for a long time.
I am rather electronics challenged. Could I request you to provide more details. What do I hook up the multimeter leads too. Can the black wire be disconnected easily? And does the care have an upstream and a downstream sensor? Woul dyou have part numbers - just in case...
 

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Registered
1991 560sec. 1969 280SL
Joined
·
1,077 Posts
Thanks Gogi. I appreciate your reply and I will do that. I know you are one of the seasoned members of this forum for a long time.
I am rather electronics challenged. Could I request you to provide more details. What do I hook up the multimeter leads too. Can the black wire be disconnected easily? And does the care have an upstream and a downstream sensor? Woul dyou have part numbers - just in case...
Has just one sensor. The black wire pulls apart connect the red probe of the multimeter to the end that goes to the ECM and the black probe to a good ground like the seat track or bolt. The Multimeter should be set to volts or millivolts. The engine should be running and at temp.
just go on ebay or amazon look o2 sensor for your specific car and buy Bosch.
 
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