How To Read OBD2 Engine Diagnostic Logs

I can get around 120ms to 200ms sampling out of TestO with 2 or 3 PID's selected. That should be almost fast enough. The only problem with that set up is that it's based on the INPA communications bus, so the fuel trims are Additive (ms), Integrator (lambda), and Multiplicative (%) and not the OBD2 STFT (%) and LTFT (%) that we are used to.

Looking at what I've written above, I might run a Pre-Cat O2 and integrator log for a bank as see what I get.

My understanding is:

• Additive is low load only. You can work out the % fuel adjustment with a bit of Math, but you need to have the base injection pulse width. I've seen 2ms used as the base pulse width. Don't know if its the same for all engine sizes or where to get the correct data.
• Integrator reports Lambda. Don't know if this is the conversion of the Pre-Cat O2 signals or the Metric equivalent to STFT? Hence the log above to investigate.
• Multiplicative is almost the same as LTFT. I've looked at this before with a car at hot idle, jumping between scanners. The numbers ae very close but not the same.

Below is part of a Cold Start log I have on file as a sample of what TestO can do.

Bank 1 Pre-Cat O2 sensor is old and lazy:

• Not cycling as fast as Bank 2
• Has a rich offset.

I understand that it is the DME that causes the O2 sensor cycling by altering the mixture just a little all the time. Its called "Dithering". If the DME dithers at the same rate on both banks, then Bank 2 is showing the correct sort of O2 waveform, whereas, Bank 1 is misreporting by missing some of the pulses.

Or it could be the 160ms is too slow and we are being fooled by technology with a pretty looking chart that is suffering from the same low resolution problem as the OBD fusion charts.

@Sapote maybe you could capture an O2 sensor signal at hot idle with your scope, so we can see the frequency of the pulses. This will help confirm my Testo data as correct or not.