Code p 304, I have done spark plugs,wires,ignition coil, top motor mount. Car has been fine for a week then the engine light came on again with same code. Car runs fine, rpm are good.

20

Asked by Oct 29, 2015 at 08:20 PM

Question type: Maintenance & Repair

Car does shake when at a stop. Not
as bad before I fixed the motor
mount.

7 Answers

37,975

Cylinder # 4 is misfiring...

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20

I know that I can't figure out what else to do. Replaced all the usual stuff. Car seems to run fine Could be a false light

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37,975

The causes are: Bad spark plug, bad wire, bad ignition coil for that cylinder, dirty or bad injector, or bad compression.

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56,855

Remove the spark plug from that cylinder and look at the tip. Sounds like the plug is fouling out. If it's wet and smells of gasoline it's probably a leaky fuel injector. If it's black and oily I'd suspect a weak valve guide seal or weak rings on that cylinder. Especially if this is an older model with some miles on it. Run a compression test on that cylinder. If it's lower than it should be (usually around 150 PSI is good) get a spark plug anti fouler. This is really a "Band-Aid" but will cure the problem for awhile. HTH. -Jim

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20

Plug was dry, not wet or black and oily. Car seems to run fine. Has a little knock when cold and shakes a little when at a stop

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56,855

What's the compression reading on the cylinder? What kind of car is this? -Jim

37,975

Compression or anything to do with the spark is all I can come up with.

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