P0304 code won't go away

toyota
tacoma

#1

I changed the coil on cylinder 4 on my 2004 V6 Tacoma and the p0304 code keeps coming back along with the hesitation and missing when I accelerate. The wires were replaced a month ago.

What now?


#2

Check the compression. If that’s good, swap your #4 fuel injector with another one. Check out the wiring harness for the injectors while you’re at it.

All of that is assuming that you have replaced the #4 plug - you mentioned only coil & wires. But, in general, a misfire is not necessarily lack of spark - its lack of combustion: compression, spark, fuel, air are all required.


#3

First I would check the spark quality of that cylinder. Then re-replace the spark plug on that cylinder…they go bad without warning all the time…and I have come across brand new plugs that failed right out of the box.

If that doesnt solve your issue then Cigroller has good advice as usual…Check the compression in that cylinder…I dont see it having low compression for no reason…but that is always good advice when trying to sort out a cylinder misfire…

The next suspect is the coil pack for that cyl…it may be going south on you…I belive you have a coil pack in this vehicle…HOPEFULLY if they used a coil pack that they divided it up into groups of two…I hate when they gove you one large coil pack…when you have an issue like this you are forced to replace the entire pack which are expensive when they include the entire range of plugs on your engine…when they break them down into groups of two yo ucan just change out that pack…IF they are broken down…you could swap one pack for another…see if the issue moves with it.

So in order I would do the following:
Test the quality of the spark from the affected cylinders wire using a screwdriver in the end of the wire have an assitant crank the engine for you with the fuel pump fuse pulled so it doesnt start the engine on you…
Then check the actual cyl #4’s sparkplug spark quality
You are looking for a fat blue spark not a weak yellow one…you can compare to a known working good plug from another cyl
Re-replace the #4 spark plug if it looks faulty at the test…re-replace it anyway…costs less than 3 bucks and you can buy just one…
Then go to the cylinder compression test
Then to coil packs…


#4

Might as well do the compression test at the time that the spark plugs are being removed for inspection. Not going to increase the amount of work that much.

BC.