02 Sensor readings obd1
Discussion
Hi
I currently have an old 94 cavalier 1.8 CNZ in my fleet and decided to get to the bottom of the high CO issue. A mountain of stuff has been done to the engine so there is no issues with vac pipes, compression, ignition etc etc, it's all renewed. The 02 sensor was replaced a few years ago but not a genuine bosch or GM part. I managed to get hold of opel scanner and a 10 pin to 16 pin cable to plug it into the opel scanner.
Got it set up and read out various parameters the car is chucking out. From what I can see the basics look ok - temp, closed loop once warm, rich when cold etc. There are no DTC codes however I am not sure if the 02 sensor trace looks that good, it's switching from lean to rich but the pulse cycle and peak and trough look a bit shaky. I'm not sure if this is acceptable or not so looking to see if anyone with good experience reading graphs knows. These were all taken about 15 Mins after operating temp was reached.
02 Sensor
Air/Fuel ratio
4 parameters graphed together AF Ratio,02, spark angle and idle air control
The 02/AF looks richer than leaner over the timeframe. Although the little graph table says lean for average.
Thanks for any feedback.
Andrew
I currently have an old 94 cavalier 1.8 CNZ in my fleet and decided to get to the bottom of the high CO issue. A mountain of stuff has been done to the engine so there is no issues with vac pipes, compression, ignition etc etc, it's all renewed. The 02 sensor was replaced a few years ago but not a genuine bosch or GM part. I managed to get hold of opel scanner and a 10 pin to 16 pin cable to plug it into the opel scanner.
Got it set up and read out various parameters the car is chucking out. From what I can see the basics look ok - temp, closed loop once warm, rich when cold etc. There are no DTC codes however I am not sure if the 02 sensor trace looks that good, it's switching from lean to rich but the pulse cycle and peak and trough look a bit shaky. I'm not sure if this is acceptable or not so looking to see if anyone with good experience reading graphs knows. These were all taken about 15 Mins after operating temp was reached.
02 Sensor
Air/Fuel ratio
4 parameters graphed together AF Ratio,02, spark angle and idle air control
The 02/AF looks richer than leaner over the timeframe. Although the little graph table says lean for average.
Thanks for any feedback.
Andrew
Edited by GrannieTwoEight on Thursday 20th August 17:23
The fact it's cycling is good news and shows that the ECU is getting credible sensor inputs and has enough control authority.
You could look at the long and short term trims to find how hard it is working to achieve that.
You can use the time scale to see how quickly the feedback loop is working. It should ideally be cycling about once per second, but may be slower if the sensors are getting sluggish.
You could look at the long and short term trims to find how hard it is working to achieve that.
You can use the time scale to see how quickly the feedback loop is working. It should ideally be cycling about once per second, but may be slower if the sensors are getting sluggish.
Production cars typically use narrowband lambda sensors which just show 'too rich' or 'too lean', and the ECU uses these to steer towards the middle ground representing the ideal lambda 1. The result will usually be a zig-zag back and forth between these two states. the better the system is working, the faster it responds, the shorter the zig-zags will be and the closer it will stay to lambda 1.
The short term and long term adaptive trim figures will show you how much adjustment the ECU had to make to achieve this. For example, if the fuel pressure is wrong then the ECU may still be able to stay around lambda 1 but it may need to make a lot of adjustments to achieve it. So the trim values show up problems that may not be apparent from the lambda signal.
If the system is broken or run out of control authority this usually results in the lambda reading being pegged one way or the other.
The short term and long term adaptive trim figures will show you how much adjustment the ECU had to make to achieve this. For example, if the fuel pressure is wrong then the ECU may still be able to stay around lambda 1 but it may need to make a lot of adjustments to achieve it. So the trim values show up problems that may not be apparent from the lambda signal.
If the system is broken or run out of control authority this usually results in the lambda reading being pegged one way or the other.
GrannieTwoEight said:
As far as I can see I don't see any parameters related to fuel trim on the list below:
This isn't OBD2! The old GM ECUs have a specific fuel correction scheme that isn't quite as easy to understand. The values with BLM in the name are the long term fuel trims (Block Learn Multiplier) and the O2S Integrator is the short term trim. These are 8 bit correction values, and a zero trim value is 128. Higher is more fuel, lower is less fuel. Google will give you more information on this as it's not quite as simple as just two values. A value of 20 for partial load condition means the ECU has significantly reduced the fuel as it's detecting a rich condition via the O2 sensor. Idle fuel has also been pulled back, though not to as great an extent.
The CN18Z is unusual in that it has an EGR valve. They can get choked up with carbon and stick open just as they can on modern diesels, so worth checking this as it would introduce an air leak which would cause the ECU to richen the mixture.
GrannieTwoEight said:
It was too high, just over, for MOT. I don't have readings unfortunately or would have put them up.
Without the right info....can't really start to do much about it.Without information on the conditions any of the above data was recorded....they mean little.
See below for test......but it's only one aspect of the test...still doesn't guarantee the emissions out the other end will be as expected if there is an issue....and that information is needed too.
https://www.youtube.com/watch?v=uYMGnvtgi8w
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