Q: Cylinder number 4 is misfiring black dry carbon on spark plug code P0304

asked by on

I have one cylinder that keeps misfiring causing the spark plug to foul out with dry black carbon so far I changed the fuel injectors, cap, rotors, wires, and plugs. Been about a year since I replaced the coil and icm. Seems to misfire going uphill and every now and then on highway and interstate.

My car has 185228 miles.
My car has an automatic transmission.

Hi there. It would appear you have covered all the bases replacing components for your P0304 engine misfire. As you already know, replacing components can be expensive and time consuming without resolution. Assuming the engine is mechanically sound, good cylinder compression and valve train appropriately opening and closing. Proper diagnoses needs to be performed. I would look toward an ignition failure, given the carbon-fouled spark plug and misfire under load.

A faulty spark plug is not out of the question. A leaking fuel injector (although new) may also foul the spark plug. An intake vacuum leak over that runner could affect the air/fuel ratio and proper firing of the spark plug. I recommend having your vehicle’s engine misfire diagnosed and repaired by a certified technician, such as one from YourMechanic, if you need further help.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Cylinder number 4 is misfiring black dry carbon on spark plug code P0304

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Helicoil fell into spark plug well. what do I need to do to get it out. thank you.

There are only a couple things to try. One way is to use a magnet like you've already tried to get into the cylinder. I'm not sure what kind of magnet you used but you may have to use a...

Q: Rough idling misfire & a thumping sound from the front of engine

Hello. It sounds like your cam timing may still be off or there may be another issue. I would typically do a compression test first. If the compression is low on only a couple of cylinders, then you have an...

Q: Rransmission slipping causing check engine light to come on hard shifting when warm only first gear is harsh

Hello. From what you describe it would appear that your vehicle may be experiencing some mild to serious transmission issues. If the Check Engine Light is on I would recommend retrieving the trouble codes, as they will likely shed some...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.