OK I would really like to test my oxygen senor that I adapted to my '88 190E 2.3. I bought the Bosch O2 sensor that supposedly fits 190's by just cutting the wire connectors and using the ones from the old sensor soldered.

I got my Craftsman multimeter ready but I dont know the specifications and where to hook the +/- leads. Any comments appreciated, thanks.

If its a three-wire, two are for heating, and one is for the current from the sensor to the engine computer. Hopefully you hooked those up correctly.

What you should do now is connect your meter to Pin 3 of the diagnostic socket and use the duty cycle reading on your meter to adjust the mixture to 45%. There are literally hundreds of posts on how to do this.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

If you disconnect the signal lead with the car fully warmed up it should read greater than .45V. The best test is to hook up a scope in parallel with the connected sensor so you can inspect the actual waveform. It should cycle between about .15V and .85V about one to two times per second at idle with a nice crisp jump between the two voltage levels.

A proper duty cycle also indicates a good sensor, but an anamolous duty cycle could indicate several problems.

When I do diagnostics, I usually test the O2 sensor first, and then look at the duty cycle.

Duke

What if it's a 5-wire? What is the 5th wire for?

TIA

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

I have tested by piercing the signal wire with the engine off so you do not short anything. Get past the outer shielding and into the center wire, if you have one of those little Hook type ends for you red lead of your VOM they work great. Then ground the black lead to your seat bolt and set meter to DC Voltage. Then start the car and it should be not moving and a steady .45 ish readinng until it fully warms up and the CIS-E system goes to closed loop operation. Then you will notice the voltage swinging properly, if the engine is cold you will most likely get a rich reading, over .45V. If you are talented enough go for a drive will glancing at the VOM once in a while. Once at speed you will notice it go up and down around the .45 reading. When accelerating it will go lean briefly and then to rich. When at WOT it should be above .8V until you let off the gas. This would indicate that your EHA and AFM are working properly. I actually set my EHA and IACV using the O2 reading. Got them back to where they should be after I screwed with them stupidly chasing down a rough idle and poor fuel economy. That was when I first started with the 190 before I realized there were other things wrong. Good luck.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....

Poking holes in the wire insulation and driving while concentrating on something else. Why didn't I think of that?

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1989 300 SEL that mostly works, but needs TLC