Misfire only p0304

gxp0514 · 07-04-2009, 01:13 AM

According to my aeroforce interceptor, I get a misfire p0304 only when driving in 4th or 5th gear when just cruising along with a little bit of gas (90 octane)
It only registers on the interceptor, and only displays the count (3 times so far) but not in the DTC section. Car just had westers update and my afr is good now but I occasionally get high 4s on the KR. Otherwise car runs great for only having 90 octane. I pulled the plugs last week and they looked great.
So, my question is should I even worry about this isolated cylinder misfirethat does not even stick around to set a DTC and CEL? This is a returnless system correct....so maybe the crappy 90 octane with contaminates is to blame. I have read of one hhr ss with only p0304 and it turned out to be a bad exhaust valve and seat. Crossing fingers it's not that.

07-GXP · 07-06-2009, 07:54 AM

I think what you are seeing is similar to what I get in the "Total Misfires" PID with the daskhawk. I see misfires when idling at a stop light, and every once in a while when cruising. However not once has this yielded a CEL or shown up as a trouble code when I check for it.

My understanding is that this is not uncommon for modern cars, particularly those with FI. I brought it up to the dealer several times and they told me not to worry, as have most people I've talked to on the boards.

Apparently the cars run towards the lean side when cruising or idling at a stop in order for better fuel economy, those giving us some misfires. After I tuned my GXP, I actually see less misses due to the richer fuel ratios, so that seems to be true.

So if the car is running good and your not throwing codes, I wouldn't be overly concerned.