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Cylinder 4 misfire

Hello, everyone. So I have a 2006 Ford Fusion 2.3l with 232,000 miles (with a used engine and transmission with 101k put on the car when I bought it 10 months ago). The only repairs I have had to do on the car were a driver’s side ball joint, passenger’s side tie rod, front brake pads and rotors, and a cylinder 2 fuel injector. So tonight I got the p0304 code when I hooked it up and the funny thing is that the car doesn’t shake or doesn’t really idle or run much differently, other than the idle being slightly lower than normal. I haven’t taken the car up any real hills so I didn’t notice any loss of power, but I don’t really want to drive the car until I get this issue figured out unless I have to. The last time the car had a misfire was when I replaced the cylinder 2 fuel injector (which I did get a code for), however, I am not getting any other codes besides cylinder 4 misfire so I don’t know what’s causing it. I have not replaced the spark plugs or ignition coils in the time I have had the car, I have also not replaced the fuel filter yet as I have only put around 6k on the car since I bought it. I’m not sure if it matters, but the CEL wasn’t flashing and it came on right as I put the car into gear when I got off work to drive home (thankfully I live right in town where I work). I erased the code to see if it would come on again when I drove home and it didn’t. Where should I start? I don’t notice the car hesitating or anything so I was maybe thinking of starting with the fuel injector and fuel filter and then checking the spark plugs/ignition coils?

So the car has 232K miles, and you don’t know if the plugs and coils have ever been changed . . . ?!

Let’s assume they haven’t ever been changed

I suggest you start off with replacing all of the spark plugs, with the exact ones listed in the owner’s manual

Then you can report back and tell us if the misfire is gone

If not, you may have to spend some money on diagnosis

Indeed, I wonder about the problem cylinder’s ignition coil and all the spark plugs.

I am in agreement with everyone else. Change out the sparkplugs first and see if the code comes back.

a misfire can be from a lack of spark, a weak spark, poor injector function, or low compression in that cylinder.

So I would start by replacing the plugs.


The code has not returned, and the engine is running fine? I’d ignore it until/if it came back.

With my Passat, I twice had extreme difficulty starting (over 10 years) with a flashing CEL and a miss code. But once I got it running it was fine. Never did anything, problem never returned. My guess was moisture in the HV wiring.