Tampa 928s

Wiring my A/F gauge:
I am looking at the connector from the LH to the Ox sensor it contains both the signal wire and a ground wire. It looks like the ground wire is used only as a shield and does not provide a grounding point to the connector itself. I need to tap into the center wire only. My question is so should the A/F gauge ground wire be connected to the the Ox sensor ground or to the Fuse panel ground.

Tampa 928s

I just measured my connector cut from th harness and both wires show a short to each other. This maybe normal due to it being referenced to ground but need to make sure.

Garth S

AFAIK, all recent 928's use a 3-wire O2 sensor ( early 928's, like my '80, use a single wire sensor): the single wire one grounds via the threaded body to the exhaust system - as does the 3-wire unit.
On the latter, the two white wires are supply and ground for the pre-heater, and not associated with the signal lead.

Tampa 928s

Yes I'm aware of that, I am speaking about the large round connector. The Exhaust side sensor connector has only one wire in it I believe, I did not open it up.

From the Lh side the large beige connector with center pin there is two wires one seems to be a RF shield on the outer case and the signal center wire that goes to the LH, both are green .

When I tapped into this for my A/F gauge on the LH side A/F started to act strange the meter went off and came back on when I restarted the car.
What I failed to notice is that the Lh connector side contained both a R/F shield and signal wire and most likely tapped in to both but barely touching the center wire, this would explain the odd readings as car was driven.

When I measured the resistance from the now disconnected Lh side Connector it showed both wires shorted together. The cable feed to the Lh does not show a short and if I measure the outside R/F wire it goes to ground. My thought was the LH connector may be either shorted or provides some type of resistance or loop back to the signal wire inside the plastic case. With out cutting it open I have no way of knowing this.

The reason I say this is there is no physical connection for the shield wire to ground As a temporary solution I connected the Ox sensor A/F gauge and Lh together it does read out when cold then after a short drive it shows a lean condition I'm wondering if the Ox sensor is damaged.

Tampa 928s

This is the Skem not sure what Schirm means but wire ends there !

Tampa 928s

Now that I confused everybody on this I'll try to explain this one more time:
Warning no responses and I will be forced to post a nude picture of myself

The Pdf, in my post shows a Circle where the Outer shield wire goes to, not sure if this indicates a pass through but the wire indicates it goes to a Schirm. I looked up the word Schirm and it means screen. Is the outer wire used as an RF shield, if so it seems to end in the LH connector. I hope I am being clear about this !

I have posted since this morning and no one has an answer, I'm trying to figure out if the LH Ox sensor barrel connector has a built in Resistor due to the fact it has two wires going to the connector on the LH barrel connector and the one signal wire out to the Female connector to the Bosch Ox sensor. Testing is showing a short from signal lead to outer wire on the now cut LH Male portion of the connector, either the connector is shorted inside the plastic connector or contains a low value resistor. The disconnected LH wire is not shorted, with the connector removed the outer wire is grounded to the car.

I'm not sure if I messed it up when soldering the A/F to it or this is normal. After I did a temp connection bypassing the connector the gauge works for a short time then goes lean. Is it possible to damage the Ox sensor by shorting the Signal wire to ground?

Tampa 928s

Maybe a picture will help look at the connector it has two wires both green.
The ox sensor only has one connector!

ROG100

For the sanity of us all please keep your clothes on.

928drvr86.5

That picture is too blurry to tell what is going on here.

928drvr86.5

There should be two connectors for the O2 sensor. The first connector, the sensor power connector, is a black one with a Mercedes symbol on the side containing a blue wire for 12V power and a brown ground wire that goes to MP IX on the Engine Block. The second connector, a large white plastic bullet type connector is the feedback from the O2 sensor to the Brain.

928drvr86.5

That means the shield wire is tied to ground at that point. The shield is tied to pin 11 on the LH and MP VIII.

Tampa 928s

I believe my barrel connector is damaged with it removed the center signal pin shows a short from the signal ground and RF ground at the connector only. Therefor both wires are internally shorted inside that beige connector.
This happened after I tapped into it and soldered the A/f meter not realizing a smaller signal wire was encased by the shielding wire. I may have penetrated the signal wire after soldering it on melting the signal wire just enough to have it short our while I drove around.
Makes me think the connector may have some type of metal ring to attach to the RF wire around the signal wire and the heat may have caused it to melt to the signal wire inside the barrel connector. They are definitely shorted but only on the connector itself.

Tampa 928s

Post note:
if I hook it up the way after seperating both wires the A/f meter does not work at all. If I hook it up just connecting the signal wires directly it shows a lean condition.

928drvr86.5

I guess if the connector is ruined you can just cut it and the female connector (from the 02 sensor) off, solder the wires together, and heatshrink over the splice. If you do that, first make sure that you milk the outside shield wire back over the outside of the green insulation and shrinktube it inplace. You don't want the sheild wire touching the signal wire in any way or it will short your signal to ground.

FlyingDog

If you are trying to be as precise as possible (with a horribly inaccurate narrowband O2) you would ground the sensor and gauge to the same place as the LH. Since a 3 wire sensor is grounded to the exhaust, it doesn't really matter where you ground the gauge.