mark@wrx

Maybe someone in the know can confirm this is correct.

Car is a MY93 WRX, I want to check the voltage readings from my AFR using a multimeter. If I take a good earth and then complete the circuit to the signal wire, will this give me the readings I want.

What should the reading be at idle? Should there be anything?
What should happen while driving? Voltage drop/rise?

Any advice welcome, thanks.

Dark Blue Mark

At idle it should fluctuate from 0 - 0.8V ish from memory. Dont think it will hit the full 1v.

If it hangs at a specific point for any length of time, there's a problem. Same if you get no reading.

MB

The_Judge

Idle - all over the place.

Cruise - all over the place (but quicker than idle).

WOT - In the region of 0.85 - 0.90, as a rule of thumb. If it's 0.85 or less, get a Knocklink and make sure it isn't detting.

mark@wrx

I am now REALLY worried! I've checked the voltages both behind the dash (AFR connection wires) and at source (lambda sensor cables) and the positive wire is reading 13.4v and the signal wire is reading the same! I have checked for crossed wires or stray strands but all seems OK. Could it be that the new zirconia sensor is f***ed before it was fitted? Car runs OK and the CO values were ok as well. Any further suggestions?

Dark Blue Mark

Thats a new one on me

Does the signal reading move at all? If it was 13v, I would have thought the overfuel off boost would be absolutely massive.

How many wires does your sensor have?

MB

mark@wrx

Its a 3 wire sensor. Red, black and white. The signal was moving slightly, I think it dropped by 0.3-0.5v then went back up slightly and carried on fluctuating. I know the car is running rich off throttle because of the pops and bangs from the exhaust (does sound nice though).

Dark Blue Mark

Im not sure on this one. I can think that its anything to do with the wiring, as they are insulated all the way back to the ECU.

Its more likely the sensor has broken down and the 12v feed has started communicating with the signal wire. I have no idea how these things fail, so im just guessing.

MB

Scott.T

iTrader: (2)

Sounds like the LM3914 IC in the AFR has gone short circuit.
13.4V is about right for the + input to the AFR (with the engine running).

I should disconnect the AFR from the Lambda and see if the 13.4V is still on the AFR signal wire.

The only voltage you should see from the Lambda is upto ~1V

However if the AFR is sticking 13.4V onto the signal wire, then it may of damaged the Lambda sensor, or at worst the ECU input.

mark@wrx

Cheers Scott, the AFR meter is disconnected and i'm still getting the same readings. I'm going to ring the garage who supplied me the lambda to see what he has to say.

Scott.T

iTrader: (2)

Why talk to the guy that sold u the Lambda ???

If the voltages at the AFR are the same with it disconnected (i.e 13.4V on the input signal wire), I would suggest that the AFR is at fault not the Lambda.

Dark Blue Mark

I think he meant he has the AFR disconnected, and taking the signal direct from the o2 signal wire, and still getting 13.4v

That would mean the o2 is at fault.

MB

Scott.T

iTrader: (2)

I would be very suprised if an O2 sensor could generate those short of voltages.

The O2 sensor generates the volatges due to changes in oxygen between ambient and exhaust gase using electrodes and ceramic materials.

It is it's own power source and does not get supply from the battery.

Unless the wires are incorrect i.e the heater has been wired as the signal.

I know the Lambda I just fitted (universal) has a note in the box detailing that the wire colour code has changed.

It was a four wire with colours :

White - Ground
Blue - Signal
Black - Heater
Black - Heater

I think these were previously :

White - heater
White - heater
Black - Signal
Grey - Earth

Which would cause the signal to be wired to the heater if wired wrong

mark@wrx

Mark, you are right about the AFR being disconnected. Scott, the new sensor is a 3 wire one, as was the oe one. I think its probably a case of different coloured wires for differrent functions, although they are red, black and white on both the loom and the new sensor. I will check this toinight.

Scott.T

iTrader: (2)

The OE Subaru Sensor is 3-Wire

White - Heater
White - Heater
Black - Signal

The 2 Whites can be checked with a meter to ensure that the heater element is still intact. I can't remember what the resistance is, but it won't be much.

Check that the heater wires are not shorted to the Black Signal wire.

The loom colours between the Lambda connector and ECU are different, but the signal wire is White with a Silver ring.

Dark Blue Mark

Scott,

That was my concern, that the signal and heater had shorted. Im sure that could really only happen in the sensor, although again, I dont know the internal configuration and whether that can happen?

You'd be pretty unlucky to have melted the 2 wires together!

Also, do you know what colour the Lmabda wire is on a 98STi, at the loom? I wired mine up the other day and am not getting anything on the AFR. I know its 136 pin 5, but thats black and green. (help appreciated)

MB

Scott.T

iTrader: (2)

It's possible you may off been sold the wrong type of sensor.


Just found this....

Three Wire

Colour Connection
Black Ref. (out)
Red Ref. (in) & Heater (+)
White Heater (-)

11014T18

Universal Titania Sensor
Output 0 to 1 Volt*



You would need something like this......

Three Wire

Colour Connection
Black - Signal
White - Heater
White - Heater

11983

Universal Zirconia Sensor
Output 0.1 to 0.9 Volt

OR

Three Wire Universal Sensor
Wire Colour Connection
Black Signal
White Heater
White Heater