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[zirk]

last Mot time the 1.4 Tigra Failed on emissions, cut a long story got it scraped though though a LPG Re Test, since then I changed the O2 sensor (1 wire type) with a Factors one with some improvement on the rough / hunting idling it had, no probs so far except the MPG seems to be going through the roof at the moment on LPG.

Did a Service on it a few weeks back, Oil, Plugs, Filter etc but still she running poor mpg, about 25% less, in the back of my mind is this nagging feeling of fitting an aftermarket Lambda, although no codes coming up.

My question is this, Ive got some known good 3 wire Lambda;s from a 3.0 MV6, ok, 2 wires are for the heater element (wont use them) so any problems using the these sensors in a 1 wire configuration or am I just having a brain f**k moment?

Chris 

[zirk]

Popped out the O2 sensor lunchtime, in case it was coked up or full of crap, its fine but has turned completely white in colour, is that normal if run on LPG most of the time (at the moment all the time as yet to fix the petrol Fuel Pump issue) 

[Kevin Wood]

I wonder about the difference in construction between unheated and heated sensors. I suspect unheated sensors are designed to capture as much heat as possible from the exhaust gas whereas a heated sensor can be more heavily shrouded. In other words, I think it's more likely to be the sensor that determines if heating is needed as opposed to the application (although distance from the exhaust valve to the sensor is also significant).

I'd say it's unusual to see carbon buildup on a sensor. They are placed where it's not enough to keep them clean.

That said, a non-DBW heated sensor only needs an ignition switched 12V supply on the heater, which should be easy to find. They aren't modulated by the ECU like the  DBW variant.

[zirk]

I wonder about the difference in construction between unheated and heated sensors. I suspect unheated sensors are designed to capture as much heat as possible from the exhaust gas whereas a heated sensor can be more heavily shrouded. In other words, I think it's more likely to be the sensor that determines if heating is needed as opposed to the application (although distance from the exhaust valve to the sensor is also significant).

I'd say it's unusual to see carbon buildup on a sensor. They are placed where it's not enough to keep them clean.

That said, a non-DBW heated sensor only needs an ignition switched 12V supply on the heater, which should be easy to find. They aren't modulated by the ECU like the  DBW variant.

I did wonder about the design between heated and non.

The O2 sensor on the 1.4 is probably no more than 7" from the Head.

Carbon build up?, its turned white, is than Carbon?

As you say the Non DBW 3 wire ones just need 12V but my understanding is its on a timer for Cold Start reasons, which also made me think they may work the same as a non heated type once warmed up?

[Kevin Wood]

White is carbon that has burnt off, I think. Normal at any rate.

I thought the non-DBWs feed the sensor heaters from the fuel pump relay or the engine management relay? So, on as soon as the engine starts. In some applications the heaters are delayed so they fire up after any condensation from the exhaust manifold has cleared. A drop of water hitting a hot sensor tends to kill them.

[zirk]

White is carbon that has burnt off, I think. Normal at any rate.

I thought the non-DBWs feed the sensor heaters from the fuel pump relay or the engine management relay? So, on as soon as the engine starts. In some applications the heaters are delayed so they fire up after any condensation from the exhaust manifold has cleared. A drop of water hitting a hot sensor tends to kill them.

Hmm, on a timer or not then, I dont know in that case, as said just a nagging feeling that the Factors Sensor I replaced isn't really doing its job or is starting to fail, and causing higher mpg than normal as the car is running sweet apart from that. Didn't really wont to fork out for a proper new GM Sensor just to prove the point, when Ive got know good ones from a Mig and cars just really a cheap LPG run around.

Might give the 3 wire one a go this weekend, otherwise guessing eGay is my friend for a matched used 1.4 GM one.

Thanks for your help Kevin. 

[aaronjb]

£22 for a 1-wire Denso sensor from here: http://www.sparkplugs.co.uk/pages/pricing/ccp/Denso-Lambda-Sensors-ccp.asp

I've not used them personally but know quite a few (read: lots) of people who've used them to supply Denso 3-wire sensors for MR2s who've not had any problems subsequently (and the MR2 is quite picky about the heater circuit if nothing else, lots of aftermarket sensors continue to throw fault codes as their heater circuit is of the wrong resistance; these don't, which makes me think they're genuine Denso).

[zirk]

£22 for a 1-wire Denso sensor from here: http://www.sparkplugs.co.uk/pages/pricing/ccp/Denso-Lambda-Sensors-ccp.asp

I've not used them personally but know quite a few (read: lots) of people who've used them to supply Denso 3-wire sensors for MR2s who've not had any problems subsequently (and the MR2 is quite picky about the heater circuit if nothing else, lots of aftermarket sensors continue to throw fault codes as their heater circuit is of the wrong resistance; these don't, which makes me think they're genuine Denso).

Thanks I'll add that to the Hit List. 

[zirk]

Well fitted the 3 wire type to it today in a 1 wire config, brimed it with LPG so we'll see what happens, seems to run ok, probably use the tank up to sus the mpg then do the next brim with a 12v switch feeding the heater cct.