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CEL - Code P305

My wife’s car suddenly started running rough. 2005 Taurus, 6 cyl, 3L, OHV, 83K miles. CEL came on and code came back as “P305 - cylinder 5 misfire detected”. As a side comment, her tachometer has been fluctuating big of late as well. Any ideas.

Well, you’re just full of Ford problems lately.

A misfire comes from any problem in getting combustion in a cylinder. The 4 things are fuel + air + compression + spark. The typical thing to do for a misfire is just check the spark plugs & wires. If those are original I would just do the plugs & wires.

If you have a compression gauge, just check it out while you’re doing the plugs.

There are plenty of possibilities, but that is the place to start.

After the plugs and wires, try the coil pack you are at about the age the original will fail. It will start on one cylinder and may move to another or multiples. All coils are in one pack. It is a really simple job on the 03 U engine I have not done the dohc. The tach I belive is separate from the crank sensor and a bad crank sensor throws a different code.