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.

A: The code P0304 is a misfire on cylinder num...

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!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Engine mifiring at higher RPMs, tachometer spiking up

Try to replace the ignition module and coil which is mounted top right side of the motor. The ignition module supplies the tach signal and the coil supplies the spark to the plugs. It is a good idea to replace...

Q: How do you remove the gas cap?

Without removing the gas cap, you won’t be able to fill your tank. Nissan makes it easy to remove and replace your cap, and even provides a handy holder for the cap during the filling process. Here’s what you need...

Q: Squaling noise

In most cases, the squealing noise from under the hood is caused by worn out or damaged belts, including the serpentine belt, AC belt or power steering drive belt. If your 2005 Altima has more than 50,000 miles, it may...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
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.