So you do this via laptop or in the car?, I am assuming with the tuner connected to the laptop using data viewer?
do I need to log a run first? or can I activate those selected pid's first
Do the run and then select the PIDs you are interested in. Again the 07 hemi and up has just about them all so you just check the ones you want to view after you have uploaded your log.
At the track, I playback my run logs via the trinity and ensure my A/Fs are good and I'm not getting any KNK. Don't want the laptop weight or it bouncing around at the track When I get home, I download them into my PC and use dataviewer to further analyze my intake temp, launch RPM and other stuff.
For me, I set up a log page with ST KNK, LT KNK, RPM, and A/F from my wb all on one page so when in playback mode I can see when stuff is happening (low, mid or high). Dataviewer will let you view them in gauge or graph form. I prefer graph where I can overlap the various PIDs over my RPM plus it has a real time clock on the bottom so I can see how long a ST KNK may last etc.
I think there are sample logs in dataviewer that you can play with and pick various PIDs to get a feel for them. Go into dataviewer and hit file, open log and mine defaults to the sample logs so yours should too.