Code P0304 should be a simple fix but it wasn't for me.

2002 Maxima 3,5, 134K miles. Replaced plugs and coil packs about 18 months ago. Been running great until code P0304 a few weeks ago. Fortunately it was cylinder 4 and is very easy to get to. Suspected coil pack and switched old coil packs on cylinders 2 and 4. Got code P0302 which reinforced my thinking it was a bad coil pack. Turns out that was a wrong conclusion. Ordered 6 ignition coils from Rockauto for $131 with discount.

Took about a week to get the Rockauto order but got them Sat evening. Replaced coil packs on 2, 4 and 6 on Sunday morning and thought my problems were over. Not by a long shot! Same code and engine running rougher than with old coil packs.

I had previously broken the tab on cylinder 4 connector and ordered a connector and a spark plug for pickup today. Decided to change the spark plug first since the engine was cold. Placed socket on plug and there was NO resistance to plug removal. I was shocked since I torqued the plugs when I previously changed coils and plugs. The engine ran very well but still not what I expected. Decided to check plugs on cylinders 2 and 6. Both were loose so I torqued them and now the car runs perfectly.

I finally got the connector replaced but that was a PITA. Didn't want to splice the wires but removal of the wires from the old connector took me a while.

I was fortunate that the code was not for cylinders 1, 3 or5. Still a little shocked that all three plugs were loose. Will probable replace both plugs 2 and 6 and get to the back plugs in the Spring.

 

how bad were your plug connectors? i have a few that are zip tied to the coil...

 

I replaced the connector on cylinder 4 but it wasn't the connectors. Shocked that all three plugs--2, 4 and 6--were all loose. Car running great now. Turns out the all plugs and coils were replaced over 3 years ago.