8 replies to this topic

[Alex]

Hai all. I just had my up and dump pipes ceramic coated, to help with heat regulation under the bonnet. Anyways, got me thinking about the O2 sensor bung, and that it relies on the dump pipe being earthed to the body (exhaust/dump hanger to body?). I had a crazy thought. Feel free to shoot me down here, as I'm not hugely electrically savvy (well, I'm no qualified auto electrician... but I know how to solder wires, and follow wiring diagrams) I was thinking that instead of wiring in the generic 3 wire O2 sensor, and rubbing back the ceramic coating to expose the metal of the O2 sensor bung and hanger to the body to allow earthing, could I instead run a 4 wire O2 sensor, wire the other wires as per normal, and hardwire the fourth earth wire? Let me know whatchya reckon. Cheers Alex

[Alex]

Just done some googling.

Found This four wire Bosch O2 Sensor wiring diagram

Was hoping to just ground the earth wire against the body, or to the engine block.

Would that be acceptable?

[RX25SE]

Alex, I cant see any reason why this wouldn't work. Assuming the O2 sensor if of a type that is compatible with then PCM. The front of the NGK O2 sensor catalouge has lots of useful information on this. Perhaps this is available through their website also. I've never bothered to look. What about running a tap down the bung to remove the coating? I would inmangine that the rest of the system would earth through the mounting bolts. Does your car run a small earth strap from the under body to the exhaust pipe? Usually these are found near the gearbox crossmember.

[Alex]

Alex,
I cant see any reason why this wouldn't work. Assuming the O2 sensor if of a type that is compatible with then PCM.
The front of the NGK O2 sensor catalouge has lots of useful information on this. Perhaps this is available through their website also. I've never bothered to look.


What about running a tap down the bung to remove the coating? I would inmangine that the rest of the system would earth through the mounting bolts. Does your car run a small earth strap from the under body to the exhaust pipe? Usually these are found near the gearbox crossmember.

Jason,

I have suspected that my O2 sensor quibbles (poor signal reading according to my subdatascanner ECU scanner) since my conversion to single turbo was a result of a poor earth. There was never a solid strap per se. The exhaust was just mounted by one hard steel mount (pre exhaust flex) onto the body. I don't know exactly how well that worked, as it was covered in paint, and I don't know exactly how well the gaskets conduct electricity.

According to the Bosch link I posted, it is optional apparently, in that it pulls earth from either metal contact, or the earth wire (rendering it "optional".

I am leaning towards the four wire O2 sensor conversion, simply to have a reliable earthing point, as long as the O2 sensor parameters are the same.

Thanks for your reply Jason

Alex

[RX25SE]

Alex,

Some additional info.
NTK O2 sensors
Hope it helps.

Cheers

[Alex]

Alex,

Some additional info.
NTK O2 sensors
Hope it helps.

Cheers

Thanks for that Jason.

I've been reading this:

http://www.bosch.com...or__Cat_WEB.pdf

Combined with the NGK/NTK document, and now the Bosch, they both provide a wealth of information!

Now... I've decided that I want a Bosch Oxygen Sensor! (I've been through the NTK ones...)

Now.... I am still at a loss to know what it is exactly that I need.

According to the Bosch Catalogue, I need a 0 258 986 502 (Three wire sensor with 12 watt heater and grounded case.)
But it's listed for a EJ205 (08/98-09/00 WRX). Nothing about earlier WRX/STi.

I'm just wondering what would be appropriate here.... (FORGET THE FOUR WIRE O2 SENSOR FOR A MINUTE...LET'S FOCUS BACK TO THE STANDARD 3 WIRE)

My options are here, for the three wire sensors:

0 258 005 726 – Three wire sensor with 12 watt heater and grounded case and special 3 slot protection tube.
0 258 986 502 – Three wire sensor with 12 watt heater and grounded case.
0 258 986 504 – Three wire sensor with 18 watt heater and grounded case.

I've also noticed that some other Subarus run the top one. With the protection tube.

I wonder why the NA's run the protection tube, and the turbo's don't?

Would I be able to run one with the protection tube, even though my car may be suited for one without?

Also... Through deduction, I've figured that I'll be needing a sensor with a 12 watt heater. I guess running one with a 18w heater be bad? Sensor out of range for ECU?

Appreciate your help Jason....and anyone else willing to help me nut this out.

Feel free to chime in too, Shiv, and Adam. My work here may also help your cases out too.

Alex

[CodeBurn3r]

the 18W wouldn't heat up correctly, so when starting the car in the morning it could give out of range, but then again it only reads the o2 when your cruising along. (closed ciruit mode i think its called)

as for the protection tube...
THIS is a bit of a read but what it basically states is the protection tube is there to protect the actual sensor by burning off soot and other contaminates that may interfere with the operation and correct readings.

if the wattage of both sensors is the same and they are both 3 wire i would use the shielded sensor myself. true the tarbo temperature probably burns most of the contaminates away where as the NA doesn't run quite as hot but its still an extra barrier from soot, and if your tune has you running a bit rich/safe this would probably affect you more.

[Adam]

Alex, you seem to know alot more about o2 sensors than i do already. I hope this sorts out our problems as it seems we both get the same code around the same time, i seem to get mine daily. Though i also get a dirty smell coming out my zorst just before it happens. As for mounting, mine is mounted in the bung and then the dump pipe is hard bolted to the gearbox. and that is the only source of earthing. But then again mine doesn't have a neutral switch wired in either aparantly :S Hope this helps you out if any Alex, its just some ramblings to let you know im reading this and will be following you closely on this one! I've been meaning to ask you about how you solved the issue and im assuming you havent yet.

[RX25SE]

Alex, I've only had a skim over the Bosch info but I would be wary of the 18w heater as this will require more current to be drawn from the ECU (unless it's supplied through the ECU power circuit). The heater has no effect on the oxygen signal sent to the ECU. The heater is only to provide fast warm up so the ECU can get to 'closed loop' operation faster. (single/ two wire rely on exhaust heat to do this) Have you read the number on the current O2 sensor? From memory they are made by ND and could be crossed referenced to another unit as a starting point. Is the OEM sensor zirconia or titania type as they are not interchangeable? What about this, to bring four wire back into the equation, run the ground wire from the sensor all the way to the electronic ground pin (there may be more than one) of the ECU?