Hello there, I have an 03 srt-4 . Pretty much stock except for exhaust and bov. I been getting the darn code P0300 ever since I got the car........I change the spark plug wires, ignition coil pack, and spark plugs. But it still gives me the code. It drives normal but I can hear the misfire while idling. I don't know what else could be causing the problem. I bought champion spark plugs so they come pre-gap at .050 already. Maybe I need to lower it to .040 mayb? Please help, Car is wasting wayy too much gas, getting like 12 miles a gallon :O

 

Change the injector!

 

Thanks!! What's the stock injector size for the car????

 

Are these platinum spark plugs? If so throw them in the trash. Get NGK Iridium Spark Plugs gap at .032-.040 depending on what you car likes. Dont forget to reset the PCM to clear out the code.

 

I ditch the champion and got me a hold of some NGK 4306 gap at .040 but still with the misfire and code.

 

Did you reset the PCM? Spark plugs could go down more also, mine is gapped at .032 you might want to lower yours some more. There could be a lot of cause to this. Here are some other causes.

Visual and physical inspection
Ignition wire
ASD relay output circuit (coil)
Engine mechanical problem
Ignition coil
Coil control circuit
Spark plug
Checking fuel pressure
Fuel pump inlet strainer plugged
Restricted fuel supply line
Fuel pump module
Checking fuel leak down
Fuel injector operation
ASD relay output circuit (injector)
Fuel injector
Injector control circuit
PCM (ignition system)
PCM