Always seems to be a forum member chasing coil status, good or bad.
Has anyone tried one of these coil on plug testers outlined in the attached PDF.
Of course the better brands are expensive however the usual chinese ones are available on e bay at reasonable prices.
They obviously would make coil testing simple & straightforward.

John Herbert
(1996 XJR)

 

See YouTube video " Thexton Coil-On Plug Spark Tester 458 " it is an old school method of testing that gives you an adjustable approximate value vs. go / no light through an outside the wire current sensing electronic gizmo . From what I understand without having done it in this cars practice a good coil at 100 % would read 30,000 volts ( correct value needed for X300 setup ) and as the coil winding wire insulation degrades from say current related heat the 100 % value goes down to say 75 % and as it goes down to say 50 % you will see faults in no fire . The old school method would give you a more accurate method of values to see where each COP is at on that 100 - 50 range . Has anyone tried wrapping the coils in Kapton tape ( an aircraft high temp insulator ) that may improve the performance of the coils and help with the current in the wells magnesium corrosion ? I also understand that by gaping the the plugs out to .038 vs .035 it decreases the current through the coil hence lower coil temperatures degrading the insulation material and longer service life . But as no coil last forever and as it is degrading you can bring the gap back to .035 to resolve a current misfire to get you though until you replace that coil . On the voltage supply side of the X300 ignition setup ( just putting it out there ) the Papa Indigo One ( PI1 ) connector wire 4 ( white pink ) on all AJ16 setups that has the corrosion problem may show voltage with a meter but is limited in how much current can get through to power the coils with enough . You can bypass that connector by crudely tapping power from that nearby fuse box terminal post and bring the voltage supply back to 100 % . Forgive the expanded reply but in case someone runs across this information it might help them along to get their cat to purr like a Jaguar

Thanks , Joe