I know it is a misfire code for the #4 cylinder and I know the flashing engine light is for a major misfire. I changed the plugs, wires and coil but I still get the P0304 code and the check engine light flashes only when I am sitting at a long red light. The mpg is still around 29 to 31 and I cannot hear or feel a mis in the engine. It still runs good. If anyone has had this happen to them or if anyone could help before the cat goes bad. Thanks

 

Could be a defective computer if you changed all that stuff and your still getting good gas mileage so cant be a bad fuel injector. Could be a bad oxygen sensor but I would take it somewhere to be looked asap . check engine light flashing is not good.

 

Is that the only code? I'd still check the fuel injector too.

 

If it was a fuel injector I think that he would be getting really bad gas mileage and it would be making puttering noises or like the fuel injectors were clogged . I would if its a clogged fuel injector just get some fuel injector cleaner and see if it fixes the problem.

 

That is the only code that is coming up. Fuel system cleaner was the first thing I tried and no change. I did notice that if I keep 1 foot on the brake and just touch the gas and add around 200 rpm the engine light does not flash. The car is a 04 SXT with 91000 miles on it. I am going to have the car scaned tomorrow. I will check the injector also. Thanks guys

 

Spark plug wire, spark plug, coil, injector or manifold gasket has a hole near the number 4 piston. I would change a spark plug wire or spark plug with a friends neon and go from there.

If you dont know anyone who owns a neon you can do this with your own parts. First take the spark plug wire from the number 4 and replace it with the number 3 spark plug wire. Go for a drive if the code changes to P0303 if so then your spark plug wires are bad. If it doesnt change you know it isnt your spark plug wires. Next I would do the same thing with your spark plugs. Just swap out spark plug 4 with spark plug 3 and go for a drive and see if the code moves to P0303.

Shane

 

your plugs or wires could be bad ones sometimes new ones end up being bad also the coilpack can be bad also. Or you can try taking the coil off and putting it back on same with the plugs and wires maybe you did not get them on correctly.