davidc1

Ok, so the other day I noticed a misfire/stumbling at 8-9000 rpm in my 03 S2000. I've checked the plugs and they are clean. They were replaced about 15,000 miles ago. NGK Iridium's. The miss is intermittent. I also notice it when just revving the engine to that rpm range. No CEL's.

This car has always eaten oil, but more than normal lately, but not a huge amount. No smoking noticed. The number four cylinder plug has a little more ash colored deposits on it than the others, but not major.

Only problem I've had recently is my secondary O2 sensor tip chopped off by the inside of the cat coming loose. I guess a lot of us have had that problem. I've replaced the O2 sensor, but not the cat yet.

Since I frequently autocross the car, and will be going to a track day at Buttonwillow in about a month or so, I gotta figure this out.

Anyone have any ideas?

Thanks!

Robert O

Not sure what exactly your issue is ,but revving your engine up to 8-9000 rpm out of gear is begging for problems.

davidc1

Why is that?

flyingtoaster

Billman250 says that you should only use OEM NGK Laser Platinum from the dealership because they are gapped specifically for the S2000. NGK Iridium and non OEM Laser Platinum may cause misfires. The box looks like this.



A couple months ago, I had a random misfire in cylinders 1 and 3. I performed a valve adjustment and those two cylinders had exhaust valves that were 4 thousandths instead of 9-10 thousanths. The other two cylinders were fine. After I adjusted them, the misfires went away.

davidc1

Well, regardless of the type of plug, the gap width I set myself properly on the Iridiums. Set to 0.041 if I remember corrrectly. The service manual says, if I remember, 0.039-0.044.

I know the car hasn't had a valve adjustment since probably 30,000miles.

But, I hear the usual sequence of testing in misfires is ingnition, fuel, intake.

flyingtoaster

Ignition comes first, but I prefer to pick off the low branches first. I am much more comfortable with valve adjustments than fuel systems or eveb gapping plugs and I lucked out but you may be right that fuel is a more likely cause. People have been experiencing clogged injector misfires.

andiamos2k

The fact that the miss is intermittent suggests that it might be an injector issue, but that doesn't make sense when considering the motor also misfires when revved freely. If not the injectors, i would think to maybe check the sensors.

davidc1

Which sensors would you suggest?

zeroptzero

oil consumption issues can cause that misfire as well, and consumption likely is worse at those rpms.

DocS2000

If you have a perfect idle warm and cold, the plugs look good and the stumbling happens only at 8+, its almost certainly a fueling issue. I would replace the fuel filter (good maintainance) before looking into the injector cycle.

Start simple and I hope you'll be able to isloate the problem.