O2 sensor testing

[steptoe]

Not sure if I read it here or somewhere else, someone claiming to conduct a simple O2 sensor test if suspected as yer problem - disconnect sensor from the equation and engine will run on a limp mode like fuel map. Reading into that I assumed it would be a middle of the road map.

I have seen an XF Falcon run black fuely smoke due to a dud O2 sensor, just yesterday had a quick look at a 90 MR2 (designation not used in France - sounds too much like sh1tty in Franch ) It has been through the learner process of diagnostics and used this and that has been swapped in, no change with a used O2 sensor being swapped in. Black fuelly exhaust, enough to make yer eyes sting bad,throat choke and need fresh air for a while after. Difficult or impossible to floor the throttle and then smoke rings as the cat disintegrates with backfire !!

Let's try the isolate the O2 sensor trick and see how it runs on a limp map. Limp map my rrrrrs ! Still runs black smoke as a fail safe not to run damaging lean, but instantly gained revability and no backfire.
Looks like a new O2 sensor will work. An interesting approach would be to tap the signal off a known healthy car of same Voltage O2 supply to see if the patient changes tune all of a sudden ??

[stork955]

G'day, there is a better way. Disconnect the sensor and put a voltmeter onto the wire (assuming it is a single wire type). You should see a fluctuating voltage between 0 and 1 volt. 0.5 is correct -the voltage will move up and down as the computer adjusts the injection pulse width. In my experience, most 02 sensor faults are caused by something else. That's not to say that they dont fail. Black smoke is typically some other item, like the pressure reg or blocked air cleaner. Check the fault codes also -what do they say?

Cheers,

Stork

[steptoe]

FPR is good suggestion, jammed shut so running injectors at a higher pressure, squirting more fuel in at a given pulse ..... yeah, may not be coincidence that swap in a used O2 sensor from not the same model car - Camry gives same result, yet to disconnect improves some things just not black smoke. It has an old pre OBDII diagnostic plug an as yet no data to suit. Owners first foray into efi diagnostics me thinks.
Maybe a 1.5 V battery with a string of diodes off it to reduce Voltage at each one could be a trick ??

[Subydoug]

A voltage divider is a better way Steptoe.

12v ---<>----take signal here for computer-----<>------to ground.
Valves 10k 400ohm


That being said the computer might chuck the shits because the signal isn't changing when it leans and richen's the mixture.

Regards

Doug

[littlewhiteute]

That won't work.

The ECM adds fuel, then looks at the O2 sensor, low oxygen (rich), ECM takes fuel way, looks at the O2 sensor, high oxygen (lean), repeats in a loop - closed loop.

Let's now add a fixed voltage, say 550mV, ECM adds fuel, O2 at stoich, ECM adds fuel, O2 still at stoich, ECM keeps adding fuel to it's STFT programmed limit.

The only answer is, replace the O2 sensor, preferably genuine.

[tambox]

The oxy sensor in my 98 outback has a fair chance of being stuffed, its been submerged in coolant for 7 months, they are not designed for that. The only time I get a "check engine" light is when I am cruising on a flat road, come to hills and it goes out. Check memory (black plugs) comes up with oxy sensor fault.

Does it only read the oxy sensor at cruise and not at idle?

A fixed voltage on the oxy sensor input may confuse the ECU, so be carefull.

[Gannon]

Yeah just replace it. According to Bosch they only have a service life of 80,000kms anyway

[steptoe]

Not my car . The O2 sensor that came on my L turbo looked genuine, maybe original, was old in years, 188,000km and had seen quite a few litres of water and coolant a few times, rested over a few years and more water. Still read nice as the new one I shoved in after reading they are a service item

[littlewhiteute]

Yeah just replace it. According to Bosch they only have a service life of 80,000kms anyway

That's correct, about average "service" life.

Not my car . The O2 sensor that came on my L turbo looked genuine, maybe original, was old in years, 188,000km and had seen quite a few litres of water and coolant a few times, rested over a few years and more water. Still read nice as the new one I shoved in after reading they are a service item

Service life is not the same as service item.

Extremely lucky if yours still works considering any water based fluid shortens an O2 sensors' life. Reason they are ALWAYS mounted between 10 and 2 o'clock on the pipe.