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

No worse than looking at the radio when driving. I had my VOM in my hand at the time and up by the steering wheel. As for probing the wires, sorry but that is all you can do and it is done by many more people than I and has been for many many years. Mechanics, Electricians, Engineers, and DIY'ers!

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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.....

This is doing something whilst being aware of multi tasking.........most idiots who run you off the road are multi tasking whilst in IDIOT mode !


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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

So who said looking at the radio while driving was okay? Once familiar with the radio, most common tasks can be performed without looking. It's hard to read a multimeter by touch.
Bullpoop. There are any number of methods for taking readings without harming the circuit. Damaging the insulation is just plain stupid.
If a million people do a foolish thing, it is still a foolish thing.

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1989 300 SEL that mostly works, but needs TLC

If you don't have the instrument ( s ) to obtain an O2 sensor reading via a plug-in, I have been tought, the correct way is to back-probe into the connector, ( a safety-pin works well ) or, if you absolutely must pierce the insulation, you should seal that spot after.

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2007 C 230 Sport.

Gee when I went to school and became and EE I was taught how to do these neat little tricks. It is called improvising. Also note that looking at a VOM while in your hand next to the cluster is the same as checking your speed, temp, fuel level, RPM's or even the clock. If you can not look at your speedo and still see traffic with your peripheral vision then you should not be operating a motor vehicle.

Sorry but any moron can check there speed and drive at the same time, so why not look at a VOM digital display. And I am not saying do this in rush hour traffic.....

As for piercing a wire, it is something that is common practive in the electrical industry, otherwise they would not make and sell regular wire probes that pierce a wire so you can check for voltage, like the standard little tester with a lightbulb in it. Now for higher voltage no you do not pierce the wire. Like when I was working on TV transmitters with over 5KV going through wiring, no you never pierce the insulation. At 12V it is ok to do without causing injury to yourself. Albeit I have been zapped by a wire with ****ty insulation on it and 7KV going through it. Those wire are tested by sliding the connector out a hair and probing at the connector. Unfortunately the way the MB connector for the O2 is you can not slide it out and probe without breaking the connection and I am not buying an MB Breakout Box to test the O2 once or twice. So you must improvise.

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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.....

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1989 300 SEL that mostly works, but needs TLC

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1989 300 SEL that mostly works, but needs TLC

Oh forgot to mention I have the O2 from the 1990 Mustang 302 on my car so wiring has already been cut to put MB Plugs on, so piercing the wire is the least of anyones problems.....

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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.....

I guess I'm one of those idiots who doesn't multi task very well. I was driving a 190E and trying the different modes on the climate control to determine what was not funtioning correctly. I drove into a curb at 30 MPH. It cost me a rim and an almost new matching tire.

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