I have a question about the ignition.

Is it a likely possibility that when a bad coil causing CEL P035N (Ignition Coil D Primary/Secondary Circuit) and engine choking/misfire(other CEL P030X),
then after changing to a new spark plug for that cylinder N but keep the same coil, only CEL P035N is shown but no more choking felt or misfire CEL.

If yes, is it because a bad coil together with an old plug(say having incorrect gap overtime or oxidation) will miss much worse that causes engine choking, while if with a new plug, despite a less than good coil, may only miss once in awhile, resulting in only CEL P035N on, but no choking/misfire felt.

I read somewhere that if the plug gap became wider or oxidized, it became a bigger load for the coil, pushing against the limit the coil can drive reliably.

Thanks.

 

As a spark plug fires, it will have wear and tear on the electrode, i.e., the metal will wear away and the gap becomes bigger.. A larger gap does require a more powerful coil to create a spark.

That said, let's bring practicality into this. The electrode of the spark plug specified for the RX is made of iridium, a fairly hard metal. The spark plug has evolved from soft copper to platinum to the current iridium to combat this wear. The changing of the metal has allowed the maintenance interval for spark plug changing to reach 100K miles.

To compliment the harder metal electrode, the higher compression ratio, the larger gap of today's spark plugs and the 100K mile replacement interval, the ignition coil has, by necessity, become more powerful. It is capable of creating a spark in a spark plug that is worn more than it should be. There are many instances of people going 150K miles on the spark plugs without problems. But no one will guarantee you can do this.

In your case, the most likely cause of your problem is the ignition coil. That is based on experience. A simple test of this is to swap the suspect cylinder's ignition coil with another cylinder. If the problem follows the ignition coil to the other cylinder, you have verified that the ignition coil is bad. If the problem stays with the original cylinder, then maybe the spark plug is bad or maybe the fuel injector has a problem.

 

Thanks for the reply.

I already confirmed the coil was bad.
originally, CEL P0354 is on as well as engine choking/misfire was felt.
When only the plug is replaced, the CEL P0354 is still shown, no more engine choking/misfire is felt. I was asking a possible reason/explanation of that.

 

Very common for original coils to fail. Part is upgraded and updated now. Be ready to change any and/or all of them.

 

120k miles (by manual)

 

Did I say it was? I was doing a generic statement.

 

Did I say you are wrong? I added the info from Manual for those who are / will be looking for this info.