Secondary osciloscope patterns can show the firing voltage needed to start and finish the current flow across the spark plug electrodes, which can be anylized to tell you much about what is happening inside the combustion chamber (like open plug wires, large plug gaps,high or low compression etc.). And this is the most important area of an internal combustion engine, the whole purpose of the engine is to produce power to push the vehicle and this is where that happens.
Primary scope patterns do not show the firing voltage level but do show burn time as the secondary does as well and this usualy is in proportion to firing voltage, the exceptions to this would be a fouled plug-wet or carboned up.
Sometimes it's easier to get at one or the other (primary or secondary) so having both capabilities is nice, also secondary can be deadly to your scope or computer, make shure you ground any leads used for secondary and dont hook directly to primary without an attenuator.
I would highly recomend the autonerdz training material, Mac vandenbrink
www.datec.us he has some free downloads, as well as full powerpoint training you can purchase or bill fulton
www.ohioautotech.com enhanced ignition system testing this is also available at auto-video. also great training at
www.auto-video.com they also have on demand online videos to purchase.
It's an awsome area of interest, pico/autonerdz has a secondary tool called mixmaster shows all cylinders and parades EI/DIS as well. I would buy it direct from them if I had it to do over again and get the support package, which is included in there scope packages last I knew. I also recomend at least 4 trace scope.
I have studied scoping ignitions for some time and your equipment will play a big role in this, definitely a book/video & hands on thing to learn! Each vehicle layout, Like fuel rail shape clogging injector inlets at ends or rail can showup in scope pattern as lean injector. get a propane tank enrichening tool so you can experiment richening and pull vacuum hose to lean it.
I should stop here, please excuse my grammar? If you want to know more ask on but too fully learn ignition anylization get training videos/books etc.
Hope this was usefull, have fun!
Wow i just noticed how old this post was Oh well. mayby your still looking for replies.