I bought my 1990 xjs last year
This year it failed air care on high nox
I checked the o2 sensors with an osciliscope and found my left sensor not working[ no sine wave. I replaced it with a new bosch sensor and it still reads low volts. I checked back to the ecm and have good continuity on pin 6 and 24 back to the sensors. I still have no sine wave on left bank . Can anybody help,please???

 

Not exactly my subject, but have you checked for a partial short to ground? Luckily you have two identical devices, so you can compare the bad with the good. An ohm-meter that doesn't push much current throught the resistor being measured is good, make sure the polarity of the ohm-meter's test leads are the same when comparing the good with the bad. The ohm-meter can also check full continuity of wiring, end to end. Tedious I know, but that's how electrical/electronc faults are. When solved, the car should improve the petrol consumption.
Leedsman.

 

Thanks for the reply. I did check for short to ground, and short to all other pins on the ecm plug. Still found no fault. I have good power and ground to the o2 heater which is telling me that my ground to the sensor is good.

 

Well then, if you've checked the up-down signal to the lambdasensor with a 'scope and all the wiring is good, it means the source/generator of the up-down signal must be defective; although I'd swap connections to the two lambdasensors to be abs. sure.
We both know the source of the problem then....
Leedsman.

 

I read up about the three wire sensor and the ground to the heater is not the ground to the sensor. I used a wire and hose clamp on the sensor , then the voltage went up to .5 volts. If I blip the throttle then I do get a spike on the scope, which is telling me that the sensor is ok. but the scope is fluctuating at .45 to .5 volts. The five wires at the ecm , two of them are o2 integrate pins . if I hook these to the scope will they read the sine wave , the same as at the front. If so the these should tell me what the ecm is seeing. The ecm might not be changing the fuel state, on that bank??? I did try the o2 sensor from the other side and it read the same.
Thanks

 

Do I read from your report that you have found an up-down signal on your 'scope for the bad side SOMEWHERE? Does it look like a sinewave but with top and bottom flattened? If so, then the problem must be something to do with getting that signal to the sensor.
You should be able to measure the heater's dc resistance both at sensor's terminals and the other end of the wiring where it goes into its origin, prob. ECU. So an ok reading at the end of all that wire, plus no short to ground (you say the power ret. is not grounded) means you can say the sensor's heating system outside the source power is ok. You can at the same time check to see if heater power is present when it should be.
It sounds from what you're saying that the ECU is trying to generate an up-down signal for the bad side when you blip the throttle, and that the good side is quite different? Just to make sure, can you disconnect the sensor temporarily to see if the up-down signal reappears when you blip the throttle? I.e. no sneaky short dragging it down. Of course, such disconnection might instruct the ECU to shut down the engine!
I hate to condemn ECUs as the micro. assy. is usually last to malfunction compared to sensors and wiring. My experience still says before blaming the ECU, check for clogged injectors, air leaks in the induction area, fuel starvation due to clogged/plugged filters. Also check every single connector associated for bad connexions -- for this I just pull out-push in the connectors a few times to see if it makes a difference. Sometimes connectors that appear logically to have nothing to do with the problem at hand can still provoke a fault. Wiring that has to move a lot -- suspicious. Wiring that gets wet a lot -- suspicious. Wiring that gets hot from other sources like engine manifold -- suspicious. And as you say, the ECM might not be suitably adjusting fuel rate. Prob. a professional might hook up another ECM to test simply for speed and because he has one to hand -- we enthusiastic amateurs are not so lucky!
As I say, not exactly my field, but hope this helps with your problem.
Leedsman.