P0304 not a coil or plug issue.
 

Hello all!

I am getting a P0304 misfire cylinder 4 on my 2003 Boxster base. This ONLY happens when I floor it from standstill or floor it from lower speeds. If I floor it while already at higher speeds it does not occur. The coils and plugs are less then 1 year old and I swapped the coil and plugs between cylinder 4 and cylinder 1 and the problem did not move.

What any you oh wise ones? Injector? Cat going bad? Thanks in advance for any help.

- Scott

Update
 

Added some Techron to the gas tank. Drove around awhile to get engine nice and hot. Still getting code flashing but now it doesnt stay on for me to check if it is still P0304. From flooring it the light flashes between 90-100 mph then goes out. Interesting... perhaps a few more Techon treatments and it will go away?

Swap injectors if the Techron doesnt clear it up.

Also check spark plug gap and double check coil click stap in plug is seated.

Side note
 

Side note...my 2003 does not have spark plug tubes so it's not that.

Thank you
 

Thank you. Will do and report back as I drive it more, likely tomorrow.

Check the coil packs for cracks. Ignore this, you already check for that, Can't delete the response.

Update
 

Forgot to also mention it is a Tiptronic. Anyway update after today's drive of 50 miles:

Flooring it from standstill or lower speeds still turns on the flashing engine light. It's consistently between 90-100 when it flashes. If I keep it floored and go over 100 it goes away. If I slow down below 90 it goes away. If I keep it in the 90-100 range with it flashing it will go solid and with the P0304 misfire cylinder 4 code.

Next fill up I will do another bottle of Techron. After that it's on to checking or swapping the injector.

I had an 03 do that one time, exactly as you described, turned out to be a worn cam lobe and lifter on the #4 intake cam. One of the two intake valves on #4 was only opening half way due to the extreme wear. Car ran fine, smooth, no noise, you would not know it had a problem unless you floored up to 6k, and then you really didn't feel it, but the "missfire detection" of the computer picked it up, flashed to CEL and set the code.

If I were you, I would swap the injector to another cylinder just to eliminate that, then pull the head cover on bank 2 and have a look at the cam and lifters..

Sorry for long wait for an update - I tried a couple of bottles of Techron over the last 2 months but no dice. Then Scott K at Fabspeed suggested trying Lucas. One treatment with Lucas and voila no more code when flooring the car. I will drive it hard this weekend and see if any change but so far so good.


- I did buy and have a spare injector to try next if the issue returns.

Sweet.

Good news.