Skip the auto shop - Our mechanics make house calls

Q: Car misfires when driving 45+ mph for extended period of time

asked by on

The car only misfires when driving 45+ mph for an extended period of time. I get error code P0304.

The code P0304 is a misfire on cylinder number four. The reason it is misfiring at cruising speed is that is when the engine is running its leanest and the coil is finding an easier path to ground than through the spark plug causing the misfire. The most likely cause is that the valve cover is leaking oil into the spark plug holes and causing the coil to short. I recommend you have a mechanic like one from YourMechanic diagnose your misfiring issue. In this situation, the mechanic will have to remove the coils and inspect for oil in the spark plug holes. The valve cover spark plug tube seals on some Nissan engines require a new valve cover to repair.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. Car misfires when driving 45+ mph for extended period of time

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: Car is idling rough and missing

This may be a sign of a faulty MAP sensor. The Manifold Absolute Pressure (MAP) sensor senses engine load and generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses...

Q: Intermittent failure to accellerate

This may be a result of a couple of different things, but is most commonly associated with a faulty throttle position sensor. The throttle position sensor monitors the throttle position of the throttle plate inside the throttle body in relation...

Q: POS Altima

These engines are known to have the timing chains stretch or jump time and cause hard starting issues like you are describing. Especially given the mileage, there is a good possibility that the timing chain may be your problem. I...

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 Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...