Erratic AFR's cold start / idle

[Volcom86]

I am having issues as soon as close loop kicks in on cold start from around 80c ECT my AFR's go erratic and hunt. Idle RPM are stable and so is idle ignition and it seems to be doing it while driving also.

 

I tried turning close loop off and once i do this my issues with erratic AFR's go away

 

Any idea why this may be?

 

Thanks

 

[Adamw]

The response from your lambda sensor is very slow, it takes over 5 seconds for the lambda to reach minimum after the minimum fuel trim is applied.  So this oscilation is caused by having the control rate much faster than the system response time.  5 seconds is pretty extreme, usually it is more like 0.5-1.0 second at idle so it may indicate there is a physical set up issue such as the sensor too far down the system or it may be a controller or sensor issue.

So firstly drop the CLL rate down to its minimum (1Hz), if there is still oscillation after that then you will have to reduce the gains too.  

[Volcom86]

On 5/17/2020 at 8:28 AM, Adamw said:

The response from your lambda sensor is very slow, it takes over 5 seconds for the lambda to reach minimum after the minimum fuel trim is applied.  So this oscilation is caused by having the control rate much faster than the system response time.  5 seconds is pretty extreme, usually it is more like 0.5-1.0 second at idle so it may indicate there is a physical set up issue such as the sensor too far down the system or it may be a controller or sensor issue.

So firstly drop the CLL rate down to its minimum (1Hz), if there is still oscillation after that then you will have to reduce the gains too.  

Thank you for the response Adamw I have changed the settings from these to the lower number at lower idle and it has significantly improved