4 wire O2 sensor

[CDeeZ]

Hey people,

It's been a while since I replaced my OE style 1 wire O2 sensor. I think it's probably time to replace it since they tend to get "lazy" with use.

Enter brainstorming session:
I'm thinking that I want to try a 4 wire O2 sensor this time for the benefits a heated O2 can yield.

I think that wiring it up should be a piece of cake. I'm thinking the wires should go like this: One wire for the signal to the ECM, one wire is the ground for that circuit to the ECM (just as a backup incase there are problems with the O2 grounding through the body of the sensor itself), and the last two wires are for the heater element circuit, one of which will go to a +12V switched power source, and the other is just another ground wire for the heater element circuit...

Do I have this right? Are there 2 grounds with a 4 wire? One for the ECM signal circuit and the other for the heater element circuit? Seems simple enough but someone please correct if necessary..

I'm planning on using ACDelco AFS75 as my new 4 wire O2 sensor..... At only 32 bucks it seems like a fair deal, plus it's actually ACDelco rather than some goofy brand noone has heard of.

[JeepsAndGuns]

You are correct, you will have the signal wire, then a ground for the sensor, then two for the heating element. 1 to power, the other to ground, doesnt matter witch one.

[RobertISaar]

100%.

amazon shows it for 32.29 with free shipping.... awesome.

[FSJ Guy]

You will love a heated O2 sensor!!! You'll be in closed loop in no time! Also, it won't get cold when driving in rain or through slushy snow.

[dyeager535]

Why the four wire vs. the three wire AFS-74?

I remember doing some reading on either thirdgen or diy-efi about the various O2 sensors that GM used, and as I recall, the AFS-74 was the "best" heated to use with the late 80's/90's stuff. Something to do with the way the sensor operates in regards to it's output voltage.

[EagleMark]

IIRC the three wire uses one wire to ground the power circut.

Four wire has a ground for power circut and ground for O2 sensor signal. Since the GM ECM already has a O2 signal circut tied into ground there is no need for four wire O2 sensor...

[RobertISaar]

know of a factory application for the 3 wire? i can confirm what it uses the 3 wires for then.

while the signal ground can be redundant, the ECM does use an individual ground circuit for reference.

[dyeager535]

here's one app:
Blazer 4x4 (Full size) 1994-1994 V8-350ci 5.7L F/I Vin K

Sorry for the formatting here.

1994 V8-350ci 5.7L F/I Vin K Four wire seems pretty cheap though, at $32 if that's an AC Delco part, it's probably substantially less than the AFS-74. Only used 94-95 according to delco

[EagleMark]

Well we just bought a 3 wire for my sons 16197427 conversion I think he looked it up as 1995 Chevy truck 4l60E.

My LT1 is a four wire 1994 Chevy Camaro, Corvette, Caprice or Buick Roadmaster.

Just from memory of doing harness's I remember seeing a pin for O2 ground seperate from other sensors but tied to same ground wire in harness from factory.

[RobertISaar]

colors might be different, but for a 94 blazer 5.7:

two white wires are used for the heater circuit, black wire is used for the O2 signal(goes to pin A10), and the ground reference is pin A12(if you were using a 4 wire, you would connect the O2 signal ground there).

[CDeeZ]

So, while a four wire may not be necessary for my application.... It can't hurt to have that extra ground wire could it? I kind of like the idea of a little redundancy, like a fail-safe.

Also, you guys are talking about pins.... Why couldn't you just ground the two ground wires under the hood somewhere rather than running a ground wire all the way to the ECM???

I was just about to order that ACDelco four wire 02 but now you all have me wondering.

that 94 Blazer was obviously a TBI application and if it used a four wire O2, then I would think you could slap a four wire O2 on just about anything TBI you wanted whether it had it or not.

[RobertISaar]

well, think of it this way: with a 4 wire, grounding of the O2 sensor is essentially foolproof. unless the wire is cut somewhere, it can't be effected by bad grounds on the engine/etc, since it's grounded via the ECM.

the 4 wire listed is also used in 96 and earlier 3100 applications, 97 switched to a different style of connector, but same sensing element.

[EagleMark]

Actually yes having an extra ground for the O2 sensor circut could be a bad thing. This is why they are usually run through the ECM/PCM. If the O2 has a differant ground offset then the ECM/PCM then readings will be affected. Grounding the extra wire to same ground lug on engine from ECM/PCM would be the way to do it.

Here's part of the instructions from the LC-1 Wideband O2 sensor explaining grounds...

2.3 Electrical Grounding Concerns

The electrical environment inside a car provides unique challenges, combining high voltages and

currents, low-voltage signals, convoluted signal paths, and variable conditions (i.e., fans turning

on and off, or starter cranking).

When using precision electronics, it is important for ALL electronics to share a common ground.

Remember that “Ground” is more than just the return path for any circuit- it is also the reference

against which any voltage is measured.

Since it is not always practical to ground every device to the exact same location, here are some

tips on grounding:

1. The BEST grounding scheme is all grounds (i.e., ECU, Gauges, LC1 heater, LC1

system, etc.) SOLDERED into a single lug and bolted to the engine block.

2. The next best is all grounds attached to the same source, as close as possible, but on

separate lugs. This is because even the corrosion between lugs can create ground

offset and noise. Incidentally, this is why many ECUs have separate ground wires for

injectors vs. ECU system ground- separating high voltages and low voltages reduces

noise.

3. Grounding to the engine block is usually better than grounding to the frame.

4. Grounding a gauge to the radio is usually bad- ground offset can vary with volume.

5. Grounding to an ECU housing is generally not optimal- housings are strapped to the

frame for shielding, but not necessarily grounded.

6. One of the WORST things to do is to ground most of your electronics to one place (i.e.

the engine block), but ground one device somewhere else (i.e., the frame). Not only can

this result in ground offsets, it can also create a “path of least resistance” for high

currents THROUGH a low-current device. This can result in melted wires and vaporized

diodes, when, for example, starter currents flow through gauges.

[34blazer]

theres one issue i have come across when using the heated O2. they arent as sluggish as compared to the single wire, which seemed to make tighter swingpoints. i had trouble with my car falling out of CL during highway cruising. part of that was my fault due to tightening up the O2 constant tables. even when i returned them to stock values it would still fall out of closed loop. i fixed it by tightening up the O2 voltage qualifier constants.

[dyeager535]

colors might be different, but for a 94 blazer 5.7:

two white wires are used for the heater circuit, black wire is used for the O2 signal(goes to pin A10), and the ground reference is pin A12(if you were using a 4 wire, you would connect the O2 signal ground there).

So was the O2 used dependent on VIN? The '94 full size Blazer I posted the info for was spec'd for a three wire, the AFS-74...

edit: Duh, I get it, wire "out" from the ECM on A12 for ground reference....