Hey guys. New here, and new to the Z. Bought an 04 roadster a week ago from a private seller. Wife and I love the car. Learned how to drive stick, just for it. Ive been up and down all the sites searching the dreaded P0300 code, but I have a specific question for it. It just started throwing it this weekend, much to my chagrin. Really bummed me out. So I'm going through the normal searches, on what it could be, and what to change. I took it to my buddy (he's a honda certified tech), just for advice on what he thought. Great guy, and knows his stuff. For Hondas anyway. He is wondering if the code is being caused by the aftermarket Stillen headers and exhaust?? He's hard pressed to say its the spark plugs, or the coil packs. I mean, the exhaust is made for the car, isn't it?? Would it cause the SES light to pop on, and the car to misfire?? Admittedly, he's not sure, and I don't know much about cars, so please don't flame me, haha. Im really hoping its not the exhaust, as I don't have access to the original. This exhaust was on when I bought it. Plus, it sounds awesome. Weirdly, the code comes and goes, which seems pretty common from searching it out. But when it acts up, it makes me real nervous.

To sum it up, has anyone had issues with the P0300 code, and an aftermarket exhaust/headers? Other than that, and K&N intake, the car is stock. Any help is definitely appreciated, as this is a big bummer. Thanks guys. Im a big believer in forums, and look forward to being a contributing member.

-Jared

 

i would change the plugs and coil packs. the coil packs can go bad. exhaust shouldn't cause any kind of misfire

 

quick search bro...

https://my350z.com/forum/maintenance...on-inside.html

 

in his defense..... and a tip to others. do a google search and at the end of it put :site my350z.com

 

Thanks for the reply. I am going to wind up going this route.



Thanks man. I actually already have that opened on another tab. Believe me, I've searched this to death, on this site, and others. Beside seeing if anyone had a more recent experience, my main question was about the Stillen exhaust, possibly causing the code. But I plan to go through that list. Thanks!

 

exhaust isnt causing that

 

Thanks guys. May have figured out the issue. My mechanic checked the codes today to see if it would even pass NYSI. It wouldnt. But he was showing me that the misfire code would clear. Then came another code (forgot what it was) and causing the car to go into limp mode. He then was telling me about the o2 spacers that were on the front and the rear. I remembered reading that they are only supposed to go on the back. Basically, we came to the conclusion that the front spacers are probably causing the issue for the o2 to trigger and then cause a misfire. Then putting it into limp mode. When they put this exhaust on, they mustve thought that the spacers go on the front and back. Goes back in the air tomorrow and we'll pull the spacers off. Im really hoping that this is it. Nothing like having the car for a week, and immediately regretting your purchase. Will update tomorrow!

 

It is not the exhaust. I've had the stillen exhaust on my car since I bought it. No lights or issues whatsoever. I don't know about the header, but it is def not the exhaust.

 

Good to hear no issues with yours. Im hoping its just the issue with having the o2 sensors in the front. Fingers crossed!

 

Well, it gave me three good weeks after removing the front spacers. Now, the problem is back. Next step is replacing the plugs since I already bought them. Its weird tho, that after removing the front spacers, that it would be fine for a bit, right? I mean, I did a few 30 mile trips with no issues, bombing around town as well and whatnot. But yesterday, on a short trip to my sons school, bam, right back to misfiring and throwing the code. What a bummer. Was really hoping it was just the spacers, but will be moving on to the next solution. Will continue to update. Thanks gents.

 

it may be a coilpack (as i stated earlier)

 

Right, I meant to mention that as well. Interestingly, I found one in the trunk after I bought it. Looks like theyve been toying with the issue as well.

 

So I changed the plugs yesterday. Pretty easy to do, just a little time consuming. The plugs 1,3,5 all were quite easy to get out, while 2,4,6 were torqued so much, I thought I was going to snap them. Weird. I also cleaned the MAF and cleaned the air filter. When I started it up and went down the road, it was running crappy like it had been, and the engine light was blinking. I pulled over to see if I could diagnose a coil pack, and bam, idle went to where it should and didn't have another issue. Thats whats been happening. It'll seem like it'll just kick in at random spots and be fine. I'll have to see if I can actually diagnose it to a coil pack when its happening again. Will update more when I get a chance. The frustration continues!!

 

Just to confirm what everyone has been saying, Neither the exhaust nor the headers would cause a misfire.
Glad you're happy with the tone though.

One thing I would check is the 02 sensor. There are ways of testing them (reading the ohms), but unfortunately since this problem seems to be intermittent you may have to wait until it's more frequent to diagnose.

 

Thanks Josh. Yes, the tone is amazing. Friend took it up the road the other day, and it was the first chance i got to hear it go up the road, and wow. What a sound.

Anyhoo, I wound up changing all the coil packs last week as a precaution. Easy enough to do. Im hoping that between all this and the 02 spacers in the front not needing to be there, that the issue is fixed. Next stop will be checking the sensors. So far, the light has stayed off and seems to be ok. I do appreciate you chiming in tho. Nice to see. Frankly, im glad it has nothing to do with the exhaust! Im not getting rid of it!