So I just bought my 2003 Honda Civic Si a little over a month ago and I love it. Last week I had an issue that my check engine light kept coming on for a misfire in cylinder 4. I figured that it was a bad ignition coil because all the plugs are brand new and I did a compression test on each cylinder to make sure it wasn't a vacuum leak or a cylinder head issue. It was fine for about 5 days and the light is coming on again. If anyone can please please please help me to figure out whats going on bc its pissing me off and delaying my plans for mods. thankss

 

i have a very similar issue, i still have yet to figure it out.

 

Did some research for you and it seems to suggest maybe some clogged EGR ports. Suggest taking off the intake manifold and cleaning the ports. This was after troubleshooting the coil packs, knock sensor, faulty catalytic converter, etc.

 

@SickSi99 thanks, im going to try and and report back this weekend. hopefully it works bc this is ridiculous lol. if anyone else thinks of anything else please let me know anyways

 

It's gonna be a pain in the to get the manifold off but hopefully that solves it. Let us know how it goes. It also says to check the o2 sensors as another possibility, but depending on what the CEL came on for, that might not be the issue. I suggest having the codes pulled first.

 

@SickSi99 I already pulled the codes and what not at my shop. and i checked the o2 sensors already. the car was bought from an old person that only put 40k miles on it over 8 and a half years so i just put in fuel cleaner to try and clean the injectors bc hopefully there just slightly dirty from the car sitting around so often. if that doesnt work ill put in the time to pull the manifold

 

i thought the VTC took care f the EGR?

 

if your spark and compression is good then you may have a bad injector i'm not 100% without looking but see which cylinder is the last to get fuel i've had 2 hondas that had a misfire issue and it was due to the returnless fuel system where the fuel hits last those 2 cylinders were missing due to dirty fuel rail and injectors...(both cars were v6) so 1 and 4 were missing

 

Idk man, just what I came up with after scanning a few threads about the same thread. This seems to be more common than people think. Other threads suggest a faulty knock sensor or frayed wiring. Some have used Seafoam treatment and still have the misfiring issue.

 

I think it could be the fuel injector maybe. Bc the dealer I bought it from changed the coil but it was a shitty one so maybe the injector they changed was shitty too. But the car has a very little amount of miles on it so maybe the injectors are just dirty.