Single wire O2 to heated O2 - how & what sensor?

[jeremy]

I'm looking at changing to using heated O2 sensors. We currently are using the stock single wire sensors, but as they are so far away from the nearest cylinder (custom headers) they don't seem to be working too well.

So I'm told heated sensors are the way to go, but our ECU doesn't have the heater plugs - can I just wire 12v to the heater wires on the sensors when the key is on? I've read that you can do just that, and also read that the sensors cook themselves if the ECU is not controlling the heaters - which is correct?

And if I can just wire 12v to the heaters, what sensors should I be buying? Are all narrowband O2's created equal?

I see RockAuto has the denso 4 wire sensors for a 94 LS400 for about USD$56 - would these work?

Any help would be great, thanks

 

[gloverman]

I use either a 3 or 4 wire ( I prefer the 4 wire) and only power them when the motor is running. Usually off the fuel pump relay. I normally have suitable sensors in stock. Not all sensors are the same - they can have different heater elements in them and there are a couple of construction types.

 

[Beezer]

I've wired mine in via ignition switched live & they've been ok so far (after about 6 months). The wiring diagrams in the Megasquirt manual suggest you can wire them via switched live (either direct or via fuel pump relay) http://www.megamanual.com/v22manual/mwire.htm . I've read that the heater circuit in o2 sensors are self regulating in that they don't draw much current when they're hot enough. And, I've read that the main reason that they tend to be wired through a factory ecu is so it can monitor the current draw on the heater circuit and raise an alarm when it's broken. I've also read that you shouldn't believe everything you read on the internet

See my thread here. http://www.lextreme.com/forums/showthread.php?t=14008 . I've been touting this a few times already today. Sorry if I sound like a broken record

 

[gloverman]

Hello - Older systems were wired to an ignition search and yes they draw very little current. The main issue is if the ignition is on for a while the sensor can be very hot and then you start a cold engine and cold condensation hits the hot sensor and that does damage. This is why I wire them only when the motor is running. Cheers

 

[jeremy]

Ok thanks guys,

So I'm guessing those 4-wire Denso LS400 sensors would work?

Anyone know where to get good o2 sensors at a good price in NZ? I can get those Denso sensors landed for NZD$85 each which I guess is not to bad.

Also, any clues on where to get the other end (loom end) of the 4-wire plug. A quick google search and it looks like the same plug is used on lots of toyotas, so maybe I just try pick-a-part?

 

[gloverman]

I would just cut them off and use a universal type plug. No soldering on O2 sensor wires.

 

[jeremy]

Ok say the factory wiring isn't long enough to reach the sensor - what are my options?

I know it isn't long enough now, but with some re-routing it may reach, or may not.

...but yep, good idea on the universal plug - and it would mean I could buy the universal version of that same sensor and save a few $s.

 

[gloverman]

You have to add the wires for the heater anyway so extend the wires on the loom or get sensors with longer wires.

 

[jeremy]

Oh, so it's just no soldering between o2 sensor and plug, but ok between plug and ecu?

 

[gloverman]

Yes thats correct. The factory loom has shielded wire for the O2 sensors but you should be able to extend the end without issue.

 

[jeremy]

Thank you both for you help so far,

I've purchased some Denso #234-4000's (a universal 4-wire sensor). I found evidence to suggest it is the same sensor as #234-4211 (the replacement for a 94 LS400 4-wire) although not 100% sure on that.

Haven't had a chance to install and test yet, but will post an update when I do (gotta get the thing running again first!)

For anyone interested in the reason why you shouldn't solder O2 plug wires, these forum threads were good reading...

http://forums.pelicanparts.com/porsche-911-technical-forum/78442-o2-sensor-alert-new-info.html

http://forums.rennlist.com/rennforu...orum/78698-do-not-solder-o2-sensor-wires.html