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Discussion Starter #1
After driving about 7 miles (2002 ZX3) the car started running rough on the way home. About half way home there was a distinct sulfur smell and the roughness got dramatically worse. Check engine light started flashing about a half mile from home.

Checked codes and got P0300, P0302 and P0303. Confirmed my suspicions of misfires.

I plan to check plugs and wires in the morning. In the event that does not clean things up, what should I check next?

Many thanks in advance for advice.

Joe
 

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Check the coil out in bright sunlight, if it has any hairline cracks anywhere on it including the bottom it is likely bad. You change coils more than plugs on the single coil assembly models.
 

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Thats What She Said
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Check the electrical wire that also plugs into the coil. those are known to crack and then start corroding.
 

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Discussion Starter #4
I appreciate the quick response, AMC49!

I pulled the ignition coil pack and examined it in bright sun. There are no visible cracks or carbon tracks. I guess this does not necessarily absolve the coil pack. I intend to check the resistances of the coil pack but don't expect any "eureka" moments.

The gap spec for the plugs is 0.50 as I understand. Plugs 2 and 3 were measured to be 0.75. I re-gapped them with no change in performance.

As the coil pack is the original, I may pick one up and swap it and see what if anything changes.

Joe
 

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Discussion Starter #5
Maybe Eureka?

I checked the coil pack resistances to ground. While terminals 1 and 4 looked like open circuits, terminals 2 and 3 each had resistances to ground around 80 ohms. That would look like the terminals for cylinders 2 and 3 have a short to ground.

Does that sound right?

Joe
 

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Discussion Starter #6 (Edited)
Resolved!

I got the coil pack today and swapped it out. Running like a top.

I appreciate the help and advice. With no exterior cracks or carbon tracks at either the high voltage terminals or on the input end, the fault must be interior. There seems to be a high short from terminal 2 to terminal 3, and as they both are on opposite ends of the same coil, there must be a short or two to the iron core of the second coil.

I've attached a diagram I found of the coil pack wiring that may help others diagnose their problems.

Joe
 

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Resolved!

I got the coil pack today and swapped it out. Running like a top.

I appreciate the help and advice. With no exterior cracks or carbon tracks at either the high voltage terminals or on the input end, the fault must be interior. There seems to be a high short from terminal 2 to terminal 3, and as they both are on opposite ends of the same coil, there must be a short or two to the iron core of the second coil.

Joe
Great!
 

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The cracks are simply a quick indicator, they do not nearly have to be there for coil to be bad as a rule...............
 
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