What is going on here ??

[Dieselman]

Hello everyone,

Could somebody have a look at this log for me and tell me what is going on between frame 13252 and 13500.

Moves from stoich to lean and then rich with a spark drop to match ?

18551


18552
18553

[joecar]

ECM is performing the catalyst efficiency test (when done, sets/clears DTC's P0420/P0430, and it sets the catalyst efficiency monitor to ready/done).

[joecar]

The catalyst efficiency tests consist of driving commanded lambda as 1 cycle of a squarewave, and then monitoring the elapsed time for the pulse to travel from the front NBO2 to the rear NBO2...

the spark timing you see changed is probably to control idle speed while lambda changes.

[Dieselman]

Thanks Joe. I have done lots of logs in the past but never noticed it before. I thought it may have been something to do with emissions