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Double check the spark plug wire firing order. The cylinder have to have voltage in a certain order. If you do not have a motor manual you can google for this information. just write for example: 2002 ford taurus 6 cylinder spark plug firing order. The firing order goes in sequence usually in a clockwise direction. For example: 1, 5, 3 ,6 2, 4 in a clockwise order. spark plug #1 wire goes to the coil then spark plug #5 wire goes on the coil in a clockwise rotation, next to where spark plug # 1 was connected. This would mean that spark plug number 1 will fire (or get voltage), then spark plug nuimber 5 will fire (get voltage), then spark plug number 3 and so on. The sequence will continue to happen over and over again as long as the car is on. Here's another tip! When it nice and dark outside, turn your car on with the hood open and look at your spark plug wires for any voltage jumping from the wires to the motor metal. Keep in mind you may have to tent yourself with a cardboard to see the voltage arcing to metal. It has too be super dark for you too see this fault. Any arcing will cause your engine to misfire and your engine light to come on. Hope this gives you a starting point to finding the problem. Good Luck.
Hi Cliff, P0304 is an error code for a misfire of #4 cylinder. This usually means that there is poor / no ignition of fuel in the cylinder and is providing little if any power (due to a number of reasons - including: poor compression, or a faulty #4 spark plug, spark plug wire, distributor, etc). In an 8 cylinder engine, that would mean 1/8 of the power is lost; for a 6 cylinder engine 1/6 of the power is lost; and so on. The more cylinders your engine has, the less likely this problem would be noticed. Loosing 1/4 of the power in a 4 cylinder engine would probably not go unnoticed for long. The unburnt fuel in #4 cylinder is being exhausted with the other cylinders and is being burned in the catalytic converter instead of the engine. If allowed to continue, it may cause the converter to fail. You should have the trouble checked and repaired before it causes other problems. Good luck!
it can be the coil for #4 each cilynder has his own coil also try to check make sure the coil is installed properly it happen to me I replaced spark plugs on my own blazer and service engine light came on #1 cilynder was not working so I did took the coil of again and make sure it was ok try to get back in place and problem fix if still doing then you can swap coils but not wires that connect the coils and see if your code reads different spark plug # if so then is time for a new coil
Is it a 4 or 6 cylinder? 4 cylinders were bad about cracked heads and leaking fuel injectors. Check compression of that cylinder and adjacent. Should be withing 10-15 PSI of each other. Less than 125 PSI is not good either.
did you put the platinum plugs back in.get a noid light test the injector wires make sure they are working . when you hook noid light up these should have a steady blink .if light dont blink just light up.you got pcm problems .if you get no lights you have open wire.besure to check ignition coils that control those misfiring cylinders.