4 wire O2 sensor

**CDeeZ** · 05-16-2012

Okay after reviewing the 7747 pinout diagram it looks as if there are two
"system grounds" the A12 and also @ D1. I found both of these wires under the hood and I have them grounded to the intake manifold, but at two different places.. Should I put them all at the same location for grounding?

So, if I were to tap into the A12, would I just figure out which one of two wires under the hood with that color scheme (black w/ white stripe) is the A12 or does it even matter since they're both system grounds… and then just strip some insulation off and piggyback the O2 ground wire onto that???

EagleMark, you say it could be a bad thing, but if it's properly grounded it should be just great right?

Okay now I'm really confused, it looks like the pinout shows that the 02 has a dedicated ground… on pin D6 with tan insulation…… If I buy this 4 wire, where do I ground it? To one of the "system grounds" (blk/white) OR, to the "GND O2" (tan)

It sounds like a 3 wire would be just fine, but if I can properly setup a 4 wire O2 I see no reason why not to go for it?

RobertISaar, I see that you said to ground the 02 circuit @ A12, the system ground as my pinout diagram is calling it… Why not use the other wire the tan "GND 02"??

**EagleMark** · 05-16-2012

Simple answer: Leave the grounds the way they are and add the heated O2 sensor ground to anywhere on engine block. If you go with four wire ground the sensor to same bolt on engine that ECM already uses, either one.

**RobertISaar** · 05-16-2012

that's why i would run the O2 sensor's signal ground to the ECM.

even if the entire rest of the ground system essentially fails for some reason, with the O2 having it's own ground reference, it will always read 100% correct. if ground isn't really ground, then the O2 voltage will shift, sending a falsely rich or falsely lean signal, depending on the shift.

my 2 cents anyways.

and i'm not sure what ECM the schematic i looked up was for, it may not have been for a 7747, there were at least 2 O2 sensor circuits i could have chosen from, both were at least slightly different.

**EagleMark** · 05-16-2012

With what Robert has posted I would not run a four wire O2 sensor on a 1227747. I've added three wire O2 sensors to 1227747 before because it is desinged for one wire from sensor going in! Then has a ground wire going out, and it works! Other 2 wires are power and ground for heater.

Use a three wire! It's been done many times with nothing but improvments!

Why try a four wire? The wire coming out of 7747 goes to ground, if you add the fourth wire from a four wire O2 sensor to it you have already passed whatever is inside the ECM like pictured above so might as well be to ground.

**RobertISaar** · 05-16-2012

technically.... you can connect the O2LO pin directly to a good ground, the 4 wire O2 sensor's signal ground to a good ground, then it's basically a 3 wire.

the only real advantage (and difference between) a 4 wire has over a 3 wire is that it doesn't rely on the body of the sensor(it's threads specifically) for the ground path. ONLY difference.

**Six_Shooter** · 05-16-2012

Wow, you guys are making a big deal out of a small thing.

MANY people have used a 4 wire NBO2 sensor in place of a single wire NBO2 sensor.

This is especially common in 2nd gen J-bodies.

The 4 wire version is much more common than the 3 wire units, generally a little cheaper too.

There is the same signal wire, an ignition wire, and two grounds, one is a heater ground and one is a sensor ground. The most common place to connect the sensor ground in a retro-fit, is to guess what, a solid ground, could be the same point as the heater ground, could be a separate location. If the ECM has an "O2 ground," which many do, this ground could be connected with that ground.

**EagleMark** · 05-16-2012

We're bored!

**CDeeZ** · 05-17-2012

My new O2 should be here tomorrow. I'll let you all know how it works out. Thanks to everybody for their input so far.

**CDeeZ** · 05-19-2012

The new O2 sensor came today. I have a weatherpack-pigtail to plug into the other side on order which sould be here tomorrow for a nice clean installation.

I was playing around with the O2 in the garage tonight trying to see if I could get the heater element to do it's thing. I have 4 four wires, two black, one blue, and one white. I tested the prongs for continuity and I got continuity from one black wire to the other black wire. THIS is the heater circuit right? I can't find a diagram of what the wires are so I'm left guessing in a retro fit application like this.

I put 12v to the 2 black wires to try to bench-test the heater element but it didn't do anything. I hope I didn't screw something up...

I'm guessing the two black wires are for the heater circuit, while the blue wire is signal to ECM and white wire is ground, but can anyone confirm this?

**RobertISaar** · 05-19-2012

you probably won't be able to do this off of color, rather pin position.

pins C and D are used for the heater. should be able to see some cast letter in the plastic.

A is O2 ground and B is O2 signal.

**FSJ Guy** · 05-19-2012

I think I asked around here about the schematic a while ago. If you google around a bit I think you'll find out which wire is the sensor and which is sensor ground.

**EagleMark** · 05-19-2012

^^^^^^^^^^^^^^^^^^^^^^^^^^^
Bottom one...

**CDeeZ** · 05-21-2012

Awesome, thanks Robert and Mark

**CDeeZ** · 05-25-2012

Okay I just finished installing the new 4 wire O2, had to wait a few more days for the right pigtail connector to arrive..

I noticed that it seemed to swing between rich and lean much quicker than the old O2 so the old one must have been pretty lazy from age..

I thought that with a four wire O2, it should go into closed loop almost immediately and stay there???? I did some cruising around town and a short blast down the highway and the ECM was in open loop more often than I figured it would be...... Am I missing something here? Could the open loop have anything to do with the fact that I have massive exhaust leaks on both collectors?? Need to get that fixed next...... Still have the stock fuel tables for now, so it was running pretty rich the whole log session.....

I wired it up exactly as you guys stated...

I'm uploading a short log, if anybody would be so kind as to review it and see what gives with the new O2 sensor, or am I just overthinking this??