V8 doing in Cylinder pressure testing, noted strange drop out of pressure, occurring at the same time on every pulse. Checked battery and ground power to sensor - both consistent at time of drop out so what the heck is going on ? Only when I looked at the COP sync and used the rulers to split into 8 did I notice that the drop out's were linked to coil firing
Then I realised that in order to avoid issues with hose removal I had used a threaded metal tube to link sensor to plug hole, so what I was seeing (I think) was the sensor shutting down as stray voltage from a coil grounding outside of the plug. Going to electrically isolate sensor from test tube in future as I'm sure it will not do my expensive scope any favours.
- but it does make me think about using a COP sensor on an earth at the cylinder head!