I wanted to align the idle RPM in open loop and close loop mode. So I started to measure and the result (although not related to the original intent) is as follows, all measurements with an oscilloscope, engine warmed, running, LUCAS P, 16ECU, USA model, V12, 1988, two connectors, 4 pin (test) and 2 pin (switch) in boot:

O2 sensors disconected from wire to ECU:
A bank - 0.6V
B bank - 0.5V
Reading disconnected wire to ECU:
A bank - 4.8V
B bank - 4.9V
O2 sensors conected to ECU, reading from connectors in engine bay:
A bank - 3.3V
B bank - 1.5V


OPEN LOOP, 780 RPM
Output on the 4-pin connector, square waves, A + B bank 1.9 V (it is all right, as described in Book)


CLOSE LOOP, 880 RPM
Reading from 4-pin connector, GW (A bank) and GK (B bank) in boot
A bank - square waves, 1.9V, something is bad
B bank - 3,7V


Result :
A bank is running in close loop mode in "map" mode
B bank is running (perhaps) in close loop mode in "O2 sensor mode"


O2 sensors are new (2 month old), ECU is refubrished.


Where to start to find solution ? Thanks

 

I had a similar problem when I changed the injector wires.I confused the places a and b banks. The engine worked poorly.
swapped the wires of lambda sensors and worked good

 

Thanks. It is true, that I made new injectors wires (old was dead). Which wires of lambda You swapped ? From engine bay to ECU ?

 

I made yesterday experience. I link A-bank lambda to B-bank wire to ECU and B-bank lambda to A-bank. Result :
Reading from 4-pin connector, GW (A bank) and GK (B bank) in boot
A bank lambda - 3,7V
B bank lambda - square waves, 1.9V




It seems, that wires for A-bank are all right and ECU too, and bad is lambda in A-bank. I will try change A-bank lambda and we will see

 

You can not read O2 sensors reliably with a DVM unless the DVM has peak hold function, you really need to look at the waveform on a scope. This is essentially an AC voltage and measuring with a DVM on DC will give not work as the O2 sensor pulses too quickly, and measuring on AC you will read the RMS value of the average of what the O2 sensor is reading.

Rich will be 0.9v and lean will be 0.1v

If your DVM has peak/min hold use these functions with DVM set to DC to measure max and min voltage

 

Yes it was reading with scope. 1.9V was rectangle wave, with max 1.9V.

 

On a scope 1.9 and 3.7 volts high is not correct. Is there a dc offset.

What are the scope settings. You need to set it to dc coupling.

Low part of the square wave should sit at 0.1v and high 0.9v.

 

These values are not from O2 sensors, are from 4 pin test connector in boot (ECU output for testing). Today I will do measure direct on disconnected O2 sensors, I will write.

 

1.9V at the 4 pin test connector in open loop is correct. At least it is on my car...

 

Yes, but not in close loop. 1.9V say, that ECU is in map mode (open loop), and O2 sensors are not reading. But I have in close loop A-bank 1.9V and B-bank 3.7V. That is bad.

 

Have you tried measuring directly at the lambda sensors? the diagnostic output is likely to be buffered and may have some gain.

Edit: Ignore that I missed the comment above.

 

I have a vague recollection that on some old ECUs a DC offset is added. That would be more obvious if a reading was taken with the sensor disconnected.

 

Ok I understand.

Swap A and B bank O2 sensors and see if the problem moves, if it does then the sensor is bad.