Skip the auto shop - Our mechanics make house calls

Q: Trouble code P0303 - 2002 Dodge Ram 1500

asked by on

I'm getting a P0303 code and I replaced the ignition coil, spark plug and fuel injector to try and curve the issue but it still misfires. And when I'm driving on the interstate and have it set in cruise control the misfire monitor does not indicate a misfire. So my question is what could still be causing the misfire in cylinder 3?

My car has 224000 miles.
My car has an automatic transmission.

A: Hello. If there is no misfire on the highwa...

Hello. If there is no misfire on the highway then you more than likely either have a vacuum leak that is causing this or more commonly a valve seat that is failing.

I usually do a compression test first. This would tell me if there is an internal failure in the engine. Most of the time this is the problem. If the compression is fine then I would do a vacuum leak test to see if there is a leak in the intake manifold gasket.

If you need to have this misfire inspected, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair this.

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・Fair and transparent pricing

Get a quote

What others are asking

Q: misfire under load

Hello there, many different faults can cause your 2008 BMW 135i to have a misfire under load. If there is a multiple cylinder misfire, there may be one of a few different faults going on. The most common faults would...

Q: Transmission does not shift properly

This may be a result of low transmission fluid or potentially a faulty transmission control module. A faulty transmission control module may cause a delay in acceleration or erratic shifting of gears. The transmission control module has various sensors such...

Q: oil inside spark plug chamber and clicking/ticking

Hello - oil is leaking from the valve cover, down into the spark plug recesses as you noticed. This causes the spark plugs to short, creating the misfire you have experienced. No doubt some of this oil leaked into the...

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...
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...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...