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WTF! Oxy Sensor 

 

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 Post subject: WTF! Oxy Sensor
Posted: Sun Mar 20, 2005 1:13 pm 
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Stupid car.

My oxygen sensor is only a few months old. I measured the voltage between it (Pin 29 on ECU) and ground today and for some stupid reason its not working even close to right. Start the motor and it starts at 0V and slowly works its way up to 1.8V in the course of a couple of minutes.

The voltage just builds up slowly. It does not at any point stick at 0.85V, or begin alternating between 0.1 and 0.8V.

Diagnostic said "Oxygen Sensor - Running Rich". Heh, there's the understatement of the year.

WTF is wrong! Can't be buggered already can it?

 

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Posted: Sun Mar 20, 2005 1:55 pm 
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This sounds like you might be accidently measuring another voltage.

the sensor is actually a frequency based signal which the Ave Dc should be in the range you were looking for though.

Try using a safety pin tapping into the sensor wiring in the eningine bay.

have a look at the earth voltages on the map connector just be be sure the MAP, IAT, TPS and HEGO are all earthed well too.
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Posted: Sun Mar 20, 2005 2:18 pm 
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Just stuck a pin through the black wire coming from the oxy sensor itself. It does the exact same thing.

It takes about a minute to get to 1V, then it rises very slowly from there onwards.

Turn the engine off and it starts dropping back down - takes a minute or so to get back to 0V also.

 

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Posted: Sun Mar 20, 2005 2:44 pm 
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Could it be an ECU thing, or definately something wrong with the sensor? Because I have a spare ECU here I could test.

 

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Posted: Sun Mar 20, 2005 2:59 pm 
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Now this is weird. Did the exact same test with the oxygen sensor unplugged. Got practically no voltage out of it 20-30mV at most.

Does this mean that the cars electronics are causing this rising voltage? (Which obviously fries oxy sensors)

 

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Posted: Sun Mar 20, 2005 5:05 pm 
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OK. Tried with the XR6 ECU in. Measuring off pin 29 again.

At start up it went from 0-1V again slowly. It hovered around 0.8v for a little bit though which would indicate correct operation wouldnt it?
This time instead of going over 1V it seemed to hover around 1V.
I tapped the acclerater lightly at one point and it dipped down to 0.6V briefly but returned back.

The white wires have 12V across them as per spec.

And once again, when the enigne was turned off the voltage slowly started dropping again back to 0.

What the hell is going on. I'd really like to know, as I'm sick of the fuel economy lol!

I don't want to replace the oxy sensor again if it's going to die on me :cry:

I think maybe my auto ECU is buggered. If that's the case I really can't wait until I get this damn T5 and XR6 ECU in.

 

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Posted: Mon Mar 21, 2005 3:24 pm 
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Yeah it seems that the standard EEC is causing the problem because with the XR6 EEC is is working fairly well. The voltage should not go above 1v unless you run extremely rich (0.9v = 10:1 AFR). At idle and while cruising around it should sit at around 0.5v which is 14.6 AFR, and then under heavy acceleration it will then start to richen up.
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