We put gas in our jeep libery 2002,,,then the malfuction indicator light came on,, took it to autozone and said it was the p0303,, changed a spark plug for us,, at times it runs rough,, light is still on,, what do we do,, at times it flashes then stays on,,

• Well there are some other things it could be other than just a spark plug to pop a P0303 code.

1. Now running out of gas can actually throw a P0303 code, just FYI.
2. Spark plugs.
3. Check plug wires. You should replace plugs and wires every couple years anyway.
4. Could be a faulty coil pack.
5. Could be a fault Oxygen Sensor.
6. That injector could be bad.
7. Burned exhaust valve.
8. Bad catalytic converter. This will put out a rotten egg smell out of the exhaust if bad.
9. could be a defective computer too.

• Check the things I listed in the order I listed. It really can be any of the. Got to put a little diagnosing work in here. You'll find it.

PO 303 is a misfire on cylinder #3

Why would someone change a spark plug?
That won't fix it
Why are you not doing your own plugs?


You buy & install new spark plugs yourself
when they reach 60 to 70,000 miles

The misfire will be an ignition issue specific
to that cylinder & if it can't be found then a
vacuum leak any number of places

Ask around & go to the best shop you
can find, not a place that installs parts that
wear over time & never comletely fail in
your lifetime,such as a plug

Hi, the misfire can be caused by a bad wire, injector, or valve. First use an oven mitt to pull the boot off the spark plug and check to make sure there is a spark jumping while the engine is running. If the spark is good, check to see if the injector is clicking. If not, check the AC voltage at the injector connector with the engine running. It should be about a volt or 2--similar to the other injector connectors. If it's clicking, it may still be clogged. Before pulling the injector, first run a compression test to see if the problem is a valve. Please see my tip at http://www.fixya.com/cars/r6715318-causes_gasoline_engine_misfires . These are genericinstructions. If you get stuck or need specific instructions for your car, please get back to me with model, year and engine info.