Hi, I am having problem identifying bad ignition coils. Full set is ridiculously expensive and challenge is identifying one which is misfiring. I identified and replaced two coils but problem is persistent, warning sign on after reset. Have I replaced right one? Or missed others? After putting air intakes and assembling everything, 2 hours later, the warning came back. Anyone familiar with the bench test process and readings for 612 coils. I believe it is identical for 430 as well. I am interest to find out how to test coils once they are out? Any good advice and idea. Regards ZK
You have "smart" coils in your 612, which have the ignitors embedded in the epoxy potting at the top of the coil. Ignitors are the solid state switches that handle the charging current of the coil and they're turned on & off by low voltage/current signals from the ECU. Since the ignitors are directly connected to the primary of the coil, there's no way of performing static resistance checks with a DVM to ensure the coils' primary resistances are uniform, although you can measure the secondary side resistances by putting one probe of your DVM on the secondary terminal, up the boot where the coil fits onto the plug, and measuring the resistance to the earth lead from there. Your best bet is to get a 12" or so "extension" HT plug lead fabricated locally, and put it between the coil and the spark plug, then put an inductive pickup type timing light on that lead, and run the engine and watch the timing light flash. If it flashes regularly, without missing a beat, the coil is OK, however if it flashes only intermittently, there's your misfire. To save time, you can do this with multiple coils temporarily. Just ensure you have a good, positive connection between the coil, extension lead, and spark plug, else you can cause damaging voltage spikes on the coil secondaries.
Thanks for the detailed explanation and instructions. I guess I'll start with testing the secondaries before attempting the HT + timing light. Does the SD diagnostic tools give any indication as to the location of the misfire?
