Q: Code P0304 (spark plug and COP already replaced - reset code and still have a miss on 4 cylinder.

asked by on

2003 F150 - 5.4L - Had an issue with P0306 - replaced the COP on cylinder 6 with an older COP - everything was fine. Ordered a set of 8 COPs and replaced all - everything was fine - about 200 miles and I started having hesitation - finally got code P0304 - switched COP 4 with CO P1 - reset code. Still had the same problem and received code P0304 still - changed spark plug - went around the block - seems ok - about 10 miles later it started hesitating and the code came back P0304. (have had issue in the past with vacuum hoses - and have switched them out - don't think that is the problem now - but not 100% sure where to go from here)

My car has 118000 miles.
My car has an automatic transmission.

If the fault is now pinned down to one cylinder, a possibility is a faulty fuel injector. Faults can be of various sorts: injector leaks, the injector driver in the ECM, the injector itself in terms of the electrical solenoid/circuit. But, there are other possibilities and all will have to be tracked down until the fault is found: Faulty oxygen sensor(s); Burned exhaust valve; Faulty catalytic converter(s); Poor compression in that cylinder; Defective computer (rare). To get this resolved, the recommended service is a misfiring diagnostic. If you request that service, the responding certified mechanic will get this diagnosed and resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.

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. Code P0304 (spark plug and COP already replaced - reset code and still have a miss on 4 cylinder.

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: How do I make a call?

With the hands free feature on your car, you will be able to make phone calls while driving. This allows you to keep your hands on the wheel. To make a phone call using the hands-free feature. Press the...

Q: What can cause my 2013 ford escape SE 1.6 ltr to hesitate when accelerating

There are a number of things that may cause the car to hesitate when accelerating such as low fuel pressure, a dirty or faulty mass air flow sensor, clogged or dirty fuel injectors, a faulty throttle position sensor or potentially...

Q: Car wont turn over clutch ism clicking

I would recommend checking your alternator as well as all fuses. Test the alternator with a multi meter to ensure that it is maintaining 13.8 - 14.2 volts while the vehicle is running. Next, use a circuit tester to test...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...