02 Sensor Wires (3 vs 4)

[ryan_george]

I'm looking through the Bentley at the o2 sensors, and I can't figure out what the difference is between the 3 and 4 wire sensors. They both have a signal wire, and 2 for the heater. There is no mention of what the #1 wire does for the 4 wire sensor.
The reason I'm wondering all this is because I wan't to know if I can use my existing sensor (3 wire from the eta) on the 'b25 (1987) that came with the 4 wire.
I've also read that there is a Mustang 5.0 sensor we can get, but it's only a 3 wire. So back to the original question...

Thanks.

[Den]

You are corect about the 3 wires. Two are the heater loop, and one conducts the signal from the O2 sensor to the ECU. I've been told that the newer 4th wire is a redundant ground in case the O2 sensor or the exhaust becomes rusty and the sensor doesn't ground itself to the exhaust.

I'm thinking it would be fine to leave the 4th wire disconnected as long as the sensor stays grounded, but I worry about frying the ECU.

I used a Bosch 3-wire O2 sensor for a Ford 5.o($40) on my 535 with no problems, so I too would like to determine the compatibility between 3-wire and 4-wire systems, or find a $40 Ford sensor with 4-wires.

[ryan_george]

I'm sure someone should know some answers... The magical 4th wire? Hopefully it is a redundant ground, and leaving it disconnected won't hurt anything.

[Den]

Well, when this Ford 5.o sensor info surfaced years ago, the story was that all the Bosch O2 sensors are the same on the business end; the only difference is in the wire pigtail. Different length of the wires and different type of connector on the end for different cars, hence the need to splice the 5.o sensor onto an E28 even though they both use 3 wires. AFAIK, all O2 sensors have the same output(0-1V).

I don't think there was s'posed to be anything special about the 5.o sensor other than that it was a 3-wire Bosch sensor available for $40 at generic parts stores like AutoZone. I think the reason the 5.o is one of the cheapest applications is that the wire pigtail is only ~6" long, and it doesn't get the "¡It's for a BMW!" markup.

I think the best solution may be to find a newer $40 application of a Bosch 4-wire sensor and splice that into the 4-wire E30. Basically just find the cheapest Bosch 4-wire sensor available and double check to make sure the sensor tip is identical to a stock E30 tip. The only difference I've heard of is that some tips might have a different number of slits, but I don't know if that makes much of a difference functionally.

I know I've seen a coulpe of guys on R3V who work in parts stores, but I don't remember who they are. If they are not able to assist, I nominate you, Ryan, to take your O2 sensor down to your local AutoZone or AdvanceAuto and sweet talk the parts counter guy into pulling a bunch of the cheapest Bosch sensors until you find a match.

[nando]

I don't see the point of fussing around trying to retrofit a generic O2 sensor when you can get one that will plug right in for $65 on ebay..

[Den]

Nando, you said the same thing in the other O2 thread.

http://www.r3vlimited.com/phpBB2/viewtopic.php?t=14482&postorder=asc&start=15

Some folks don't mind splicing a few wires to save $25+. You can do it with the parts off of the car, say, on the kitchen table while drinking a case of beer, good beer, that you bought with the $25.

Also, being able to pick up a part locally on a Sunday when the weather is nice and you happen to have time to install it is more convenient to some.

[Den]

Okay, Ryan, here you go:

http://www.partsamerica.com/ProductDetail.aspx?mfrcode=BOS&mfrpartnumber=13275

Bosch 13275
Oxygen Sensor: Four Wire; Heated

http://www.boschusa.com/AutoParts/FAQs/OxygenSensors/

Q. I have a Bosch original equipment 4-wire sensor. What do the wire colors mean?
A. All Bosch 4-wire sensors have a black wire for the signal, a gray wire for ground and 2 white wires for the heater. Note: the wire colors and functions on non-Bosch sensors are not necessarily the same as on Bosch sensors.

http://www.boschusa.com/images/OxygenSensorInstall.pdf

Bosch FAQ on splicing

http://www.humanspeakers.com/audi/tricks.htm

1: 4-wire Universal O2 Sensor. I got this one at the local FLAPS for $45: Bosch 13275
BTW-the 4-wire is a good upgrade to the 3-wire, the difference is that the 4th-wire is an additional ground to the chassis, the 3-wires rely on a ground through the sensor body into the exh. manifold (or whatever they are threaded in), the 4th wire ensures that corrosion never diminishes the ground on the sensor body.

http://mymiata.paladinmicro.com/Miata4-WireO2.htm

Heated O2 sensors (requiring 3-wires) were designed to keep the sensing element heated to it's optimal temperature--the 4-wire sensor adds the benefit of a dedicated output signal ground wire (1 and 3-wire sensors use the exhaust system as the signal ground path).
. . .so I set out to find a suitable 4-Wire Sensor.

Autozone had the Bosch p/n 13275 sensor I had seen mentioned on Miata.net and elsewhere for $34.99 (1/2004, it's $39.99 now.)
This sensor is an OEM replacement for some mid-90's Chrysler products, and comes with a very nice male connector, and pre-loaded with anti-seize compound.

[ryan_george]

Wow, that's exactly what I wanted to know. You're the man Den. 8)

[kowalski]

i got a generic bosch 02 sensor from lordco for like 40$ or somthing like that it was a 4 wire, if theres a part number on them ill get it for you guys... anyways good luck.

[E30godz]

why dont you just ground the 4th wire....