I've recently switched from HKS 264/272's to GSC 280's and am getting the famous P0300 misfire code. It only comes on every few days. You guys running 280's without getting the code, can you please share your fuel & timing map in the range from 0-1250 rpm and load 10-30? I've bumped up timing to 9* in those cells and added 10% fuel hoping it'll cure it but still no go. Idle is at 1100rpm and is idling fine without stalls. I'm running NGK BPR8ES. I've tried gap 0.022 and 0.024 without success. Thanks

 

with 280 cams you might want to try the bpr9es heat range plugs or go with the hks m45i which is the same heat range but a little bit cheaper that the ngk's. that way a lot more heat with escape the chamber and you wont have as much det/misfires from plugs going out of wack on you.

 

Do you have cam gears and if you do, what are they set at?

 

Thanks for the replies guys. I don't have cam gears.

 

I have comp 280's and BR8ES, without the protruded tip, try those I heard the 9's foul out pretty easy

 

You did investigate the tranny first right? The PO300 code is usually a result of a worn input shaft endemic to 03's.

Rarely is it caused by actual ignition or misfire problems. It can become worse if other things are are changed in the rotating mass of the engine like cams, clutch,etc, but it's not impossible the cams or instal may have done something the sensor doesn't like.

My PO300 problems really took hold after a new clutch instal and I'm currently in the process of getting a tranny re-build.

 

I have HKS 280's and Cam Gears, used to have the Po300 at low cruise and idle situations.

 

I think this is where I went with a DLI-2 from HKS. Took care of my problems.

 

Well...prior to install of new cams, I've never gotten the code cause it wasn't as lopey as the 280's. I have the twin exedy and had no problems with the HKS. After install, the code came on which is probably due to more vibrations from the 280's. These are very lopey. By running rich at idle, it's not as lopey but is still very noticeable to the ears. So what are you guys running for timing and fuel in those range mentioned above?

 

So what did you do to fix it?

 

03' + PO300 = worn input shaft. Search and fix your car.

 

For me was to run lower timing in the top left low load, low rpm section. No more than 7-8*

 

Thanks, I will give the lower timing a shot.

 

I needa try that too... I have like 14ish to keep vaccuum up. I needa spend more time on this thing...

 

TTP is tuning my car with GSC 280s, at first I had the code, one map later and it was gone