Ignition Coil Waveforms


The ignition coil current waveforms can be monitored using a relatively inexpensive scope and current clamp. This technique can be used to diagnose problems with individual coils as well as some spark plug problems. The following PDF shows known-good ignition coil current waveforms as well as what they look like under a few fault conditions (ignition coil open and ignition coil short).



Fuel Pump – Current Waveform


The health of the fuel pump and its operating speed (RPMs) can be rapidly assessed by a quick look of its current waveform. The shape of the current waveform, pump speed and average current draw are good parameters by which to diagnose a failing fuel pump.  Details of the procedure and known good fuel pump waveforms are contained in the following PDF file:


Relative Compression Test


The relative compression test monitors starter current (via a current probe and scope) during cranking to get a quick gauge of the compression of each cylinder relative to the other cylinders.  This is a quick and easy test which can be used to check for any significant loss of compression in a cylinder.  More details, including known good waveforms are in the following PDF file: