Peak pressure can be a pretty good gauge of TDC. Just have to be certain that is a good well sealed cylinder and the engine speed is slow.....cranking or idle.
We also have an FAQ Document for the standard version of PicoScope which is for our Test and Measurement PicoScope models, but can also be used with the PicoScope Automotive software.
This covers a number of items from connection issues between the scope and the PC to limits placed on the number of samples that can be collected for a waveform.