Car is an 06 S Type R. Had some codes a while back stating cat issues. Had mechanic tell me it's likely the cats. Cleared them to see if they'd come back. Later on get a cylinder 4 misfire issue. Cleared it again, hasn't returned in several weeks. Don't remember the exact code numbers but still trying to figure out what the issue is. Thinking the cats might need replacing. Which is unfortunate since the car has like 50k? miles. Maybe just O2 sensors? Anyways, while I'm still determining the issue, I'd figure I'd start shopping around a bit for parts. OEM cats are ridiculously expensive. And the magnaflows that everybody recommends on this site are not CARB compliant. I'm thinking I need to find some used cats but that's been proving to be kinda difficult. What other options do I have? Any chance somebody can verify passing CA smog tests with the 59975s everybody likes so much?

 

Misfire is probably the coil.

What actual problems do you have now?

Good place to start is fuel trims and an elm327 will let you look at them.

 

Hm...since you mentioned the ignition coils...the only issue that I have is that on occasion, the car takes like 5 or 6 cranks to start. Searched for a few minutes and, if I'm not mistaken, seems to be semi-consistent with coils? Possibly spark plugs? I'm reading further into it and will be checking fuel trim levels today as well. Thanks for the bump in the right direction.

 

Always suspect coils on these cars not plugs as 95% or so you'll be right, partly as the plugs last 100K miles.

It may not be coils but at least swap any suspect ones.

Might be fuel filter, dribbly injectors, an air leak, etc. Filter is easy and cheap. Fuel trims through a cheap OBD tool like elm327 will let you see air leaks.

 

Check fuel trims. Idle were -1.6-0.8. I was using Torque Lite and seemed to only have 2 readings. Picked up the PRO version and it seems to have more sensors which are better defined. It also picked up a P0430 code that, for some reason, wasn't showing up on the lite version. Didn't have a chance to really warm up the car and do some idle readings and 2,500? rpm readings as some of your older posts have shown. Will do that tomorrow.

And probably not related, but the filter was pretty filthy. And apparently the old owner switched to K&N and removed the baffle.

 

You should get both short & long trims per bank so hunt round Torque for the others

If you avoid clearing the codes you could see if all the monitors set. If all you get on a regular basis is P0430 then can't be much wrong other than may well need one cat - junk yards any good?