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02 Civic EX - Codes/Cat code/Misfire

Hi. Have an 02 Civic EX. Engine light has been on for over a year, runs just fine. Reading misfires on 3 cyl, and cat code.
I have since: changed all plugs and coils, changed both front and rear o2 sensors…switched coils around to see if code misfires changed (yes).

I see this is a common problem but no one has a solution…wondering if anyone came up with one yet?
I’d rather NOT change the cat converter and pay for that only to find out the light stays on. Need to smog so I can sell!

Just to clarify this a bit. are you saying the misfire is on 3 cylinders or on Number 3 cylinder?

Well if it has been mis-firing for a year you may indeed need a Cat.

switched coils around to see if code misfires changed (yes).

What did the code mis-fire change to? That should tell you the problem followed the part.

You already know the solution. You’ve just chosen not to do it. Perhaps you really mean “no one has a solution that won’t require me to buy a new cat converter”?
(1) new cat converter.
(2) new coils.

The protocol is to deal with the lower # trouble codes first.
So if you fix the misfire (likely code P0303) then the cat code (P0420) may go away on its own if the cat isn’t damaged.

If the problem is related to tight valve lash then cylinder head work may be needed and if that’s the case then ignition components and converters are moot points until that issue is resolved.

Agree with ok4550. If you’ve never had the valves adjusted, that could well be the problem.

Have your mechanic do a compression test on all cylinders. A low compression number on a cylinder means that cylinder probably needs valve adjustment. And if the problem persists, the head may need to be removed in order to replace a burned valve. Burned valves result from driving the engine too long with a valve out of adjustment, resulting in a persistent misfire that won’t go away until the burned valve is replaced.

What the heck?

You swapped coils around, and the misfire moved from #3 cylinder to whatever cylinder you moved that coil to

That means the #3 coil is no good

Replace it under parts warranty, if that applies

Then proceed on from that point

As for the oxygen sensors, what brand did you install?

You have no chance of resolving that P0420 cat code until the misfire situation is completely resolved