Trouble Diagnosing a Misfire on My 2012 Honda Civic - Need Advice

Hi everyone,I am struggling to diagnose a persistent misfire issue on my 2012 Honda Civic (1.8L). The check engine light is on, and it’s throwing a P0302 code, indicating a cylinder 2 misfire. I have already swapped the coil and spark plug with another cylinder, but the misfire stays on cylinder 2. Compression test shows all cylinders are within spec. I also checked the injector for cylinder 2 by swapping it with another cylinder, but no luck—misfire still remains.I am starting to think it could be a wiring or ECU issue,,, but I am not sure how to proceed.

Should I be looking at the injector wiring harness next, or could it be something else like a valve issue: ?? I have also heard about issues with the EGR valve causing misfires, but I haven’t checked that yet.Any advice or suggestions on what to test next: ?? I don’t want to just start throwing parts at it, so any guidance would be really appreciated....!  I also read this thread  www.justanswer.com/honda/a0qs5-2012-hond...c-si-getting-code-p- react-native 303.html but couldn't get enough solution so I am looking for more help.Thanks in advance.

David Miller

davidmillerdavid wrote:

Hi everyone,I am struggling to diagnose a persistent misfire issue on my 2012 Honda Civic (1.8L). The check engine light is on, and it’s throwing a P0302 code, indicating a cylinder 2 misfire. I have already swapped the coil and spark plug with another cylinder, but the misfire stays on cylinder 2.

Did you check the ignition coil for spark output?

Compression test shows all cylinders are within spec.

What is spec, and what were the exact compression measurements of each cylinder?

I also checked the injector for cylinder 2 by swapping it with another cylinder, but no luck—misfire still remains.I am starting to think it could be a wiring or ECU issue,,, but I am not sure how to proceed.

Are there any codes stored other than p0302?
​​​​​​​Is this a constant miss that you can feel all the time, something that comes and goes under certain conditions, or only an engine light to let you know there's a problem?

Swapping coils, injectors and spark plugs will not help if you have wiring issues.

might also want to test for vacuum by that cyl

Like Noah was asking, it'd be more beneficial to know when the fault sets. Having the Freeze Frame data for the P0302 would be even better.