[mwebb]

using a pizeo type differential pressure sensor in the exhaust
green trace

at idle
blue trace is spark from a 4 in 1 coil pack , 1 coil is not outputing any secondary spark as seen in the waveform by 1 missing spark signature every 4 spark events -
note
in the exhaust after the combustion event that did not happen
there is an increase in pressure as the fuel that did not combust , burns in the hot exhaust along with the 02 that was not combusted in the combustion event that did not happen .
junk burn , injector is working .

another way , change in crankshaft speed as measured by alternator out put , read text bubbles
the image above was culled from the image below , what you thought was "alternator ripple " is really change in alternator output due to variation in crankshaft speed

think out side the box -