how to test lambda sensor?

[Juz]

how do i check if my lambda sensor is faulty, without actually buying a new one first?

i have a multimeter... but the lambda sensor connector behind the rear engine lifting eye only appears to have 1 wire in it?

[ianelvar]

Hi

Test output voltage relative to battery negative. It\'s got specs and a diagram on page F-185 of the \'94 factory manual if you need them.

"On deceleration 0.0V - 0.4V
 On acceleration 0.5V - 1.0V"

HTH

[Prof]

As above - but you need to make sure your multimeter is a high impedance input type (most digital ones should be ok for that).
 
The stock Lambda sensor spends most of it\'s time in one of 2 states - showing either rich or lean.  When the car is in cruise (1500-3500 RPM, no boost) it will rapidly fluctuate between the 2 extremes giving an average of about 0.4-0.6V on the meter, but some digital meters sample the input and give momentary values which may be misleading.  If you have a cheap A/F gauge handy, it will oscilate back and forth between rich and lean when you are on cruise, will go rich when you kick down, and lean when you lift off.
 
The other thing to check is the ECU codes - the car will report faulty o2 sensor for a missing or shorted sensor, and feedback loop error if it\'s not returning expected values - can\'t remember what the fault codes are off the top of my head.

[pdtaylor18]

Also if you are ensure of its condition and maybe never changed then worth the cost to get a new one.

[Juz]

i don\'t have a factory/service manual. i have a digital multimeter but couldn\'t figure out how to test the voltage from the lambda with there only being 1 wire! not the foggiest clue how to do it

so i\'ve just bought a new lambda and fitted it anyway, only done a couple of miles since fitting so i don\'t know whether this has solved my overfueling problem yet. but i was wondering is it possible to gain any clues from the condition of my old one what might have been causing the overfueling?

the sensor itself is covered in a white coat with black at the base. if the lambda itself was the cause of the overfueling it should be better now with the new one, but if something else caused it and then the running rich caused the lambda to get into this state, does the colour indicate anything in particular?
if something else is causing it, how long do you think i would have until the new lambda i fitted goes the same way?

[ianelvar]

Voltages on a car are always measured relative to the battery negative terminal unless otherwise stated. So stick the black lead of the meter on that, and touch the red one to the single wire from the lambda. Factory manual is here:
That lambda looks quite normal. What\'s the actual problem?