I recently did a tune up on my 5.4 and as per my earlier post "5.4 idles rough and stalls" I am suspect that one of my COP's may not be fireing what is the best way to test them?

 

Put them in a properly operating engine and see how they work.

 

Try this........

One at a time disconnect them from the wiring harness, being careful to not damage the connectors. Working COP's will cause add to the miss noticably, the defective one will cause no change at all (when disconnected).

Replace with an OEM from a good source such as Ed The Parts Guy (advertises here), Rock Auto or if you enjoy a decent discount at the local stealership they'll do too.

Anytime you replace a COP the boot should also be changed---and be sure to use plenty of dielectric grease to keep them pliable and sealed from moisture leaking in.

HTH

 

you can pull them out one at a time, and ohm them out at the connector. usually you need the test them at 20k and i beleive 200k. correct me if im wrong. then u just need to get the specs. someone must have them on here. if not call the dealer and they should tell you.

 

I've not had much luck testing with a DVM----tested a suspected bad coil, it showed continuity yet still seemed to cause a misfire. Replaced it and the misfire was cured.

I'm thinking any test at the connector terminals would measure the primary coil only----the secondary one not being tested at the same time. There is a test of the secondary to the primary for a short but generally the one-by-one disconnecting seems to work reliably---it did for me anyway, maybe someone can give us a known better way to bench test COP's ?

You can also test the COP's as we tested ignition systems with distributors and plug wires too. While not the most scientific of tests it does help determine how well its operating without sophisticated 'scopes and other analyzers. Connect a COP to the wire harness connector, boot also removed with the lead loose and while carefully holding the COP place the lead close to a ground such as the head. Start the engine and observe the spark that jumps from the coil to the ground-----a good coil will be a bright orange all the way to blue which indicates relative voltage. If testing several you might notice differences in the color of the spark and if the distance is kept the same you have an approximate idea of that COP's performance.


This isn't the best of tests but it can be useful if in doubt-----or you're just curious. Just BE CAREFUL-----these things throw enough juice to rock your little world for a few seconds!!

 

Testing with an ohmmeter will only tell you if they're completely open or not. Since almost all COP that fail don't have that problem, testing them with a meter is almost worthless.

Plug 'em into an easy-to-reach cylinder and test drive them one at a time.

 

I always had luck testing with a dvm, going between tests from primary and secondary. Maybe its just me. but either way its def. a way to try that only takes a few minutes of your time.