P0304 Code Season 12 Episode 01

Hey All,

2006 Preruner with 4.0 V6. 457000ish total miles (25,000 miles on rebuilt motor).

I got the P0304 code. Replaced the coil. Reset code by removing the battery neg cable for about 15 mins. Ran fine for a day.

Next morning, Starts running like crap, code comes back. Now I replace the spark plug. Runs fine. Turned off the code later that day (when I was away from my house and it wasn't 6 in the morning because my stupid alarm goes off when you reinstall the negative cable.)

Ran good all the way home from work and to work the next morning (45 mi one way).

Went to leave work tonight and the damn light comes back on. But it runs fine.
WTF???

I'm hoping it will get me to work and back tomorrow.

Any ideas? Possibly the wiring to the coil? It is the factory original wiring as far as I know. (Where does the wire from the coil end up at on the non coil end? My luck behind the motor on the firewall.)

Everything appears to be OK since I was all over the top of the motor replacing all the coils. All the spark plugs are new as well.

Help!

 

Have you checked if you have the same code?

An issue on any of the coil circuits would set a P035x code

 

It always comes up P0304. On two separate OBD II readers.

 

By the way, I'm in the Phoenix AZ area and it started getting into the 90s during the day. If that matters.

 

If it only runs rough on a cold start or after sitting for an extended period I'd check it for a headgasket leak by pulling the plug on the offending cylinder, pressurizing the cooling system with a pressure tester, letting it sit several hours or overnight, then looking in the cylinder with a borescope for coolant.