Car has randomly been throwing P0304 (Cylinder 4 misfire) code, intermittently. Been back to the dealership approximately six times for this. They have do e nothing and been of no real help in permanently solving this issue. The check engine light (P0304) comes on for about 20 miles and then goes back off. The dealership has had the vehicle several times, with the light on and with it off. They assured me after testing the vehicle that the problem was rectified, each time.

Fast forward from 32000 miles to 53000 miles. The vehicle is know showing P0430 (Catalyst system efficiency below threshold), P0304 (Cylinder 4 misfire) and P1315 (misfire excess emissions).

My question is, where do I go with diagnosing from here. I refuse to go back to the dealership and waste time and money. Can anyone offer some repairs to correct the problem(s).

Thanks in advance for any input

 

They sound awful.

Worse, sounds like the continued fault has caused severe catalyst damage.

At the least swap coil #4 with another and see if the fault moves. If it does you know to get a working coil instead of the one you moved. If it doesn't you know to start checking plug, wiring, etc for #4.

I'd also follow posts about fuel trims so you know what they are and what they do.

 

That's what I was thinking. I was going to purchase a new coil and swap it with the cylinder that hass the issue. I have been looking for an accurate supercharged V6 cylinder orientation diagram (to locate #3 and #4) but I can't find much information on the subject for a 3.0l supercharged V6.