2001 Taurus code 303 & 304

[lgraham5400]

Can someone tell me what these codes mean and give me a step by step check list to troubleshoot the problem. I know they are telling me of cylinder missfires but need to know the possible causes and the order to check to find the problem.

[shorod]

For future reference you should include the entire code number. In this case, they'd be P0303 and P0304. This will help others as they search the forum for threads for the same codes they are experiencing.

As you mentioned, these codes indicate misfires on cylinders 3 and 4. On your Taurus these will be the cylinder on the driver's side back of the engine, number 3 (firewall side) and the passenger side front of the engine, number 4 (near the belt). The first think to check would be the spark plugs and spark plug wires. If the car has a lot of miles on it and the plugs and wires are original, start with a tune up.

You could also try swapping those spark plugs with other cylinders. When you pull the plugs, check them for signs of unburned fuel. If the misfire codes follow the spark plugs, the problem is likely bad spark plugs. If the misfire remains on those cylinders then try swapping the plug wires with other wires of similar length. Notice if the misfire codes follow the wires or remain on the cylinders. The next test would be to confirm spark from the coils for those two cylinders. If they have good spark, both at the coil at at the end of the wire that connects to the spark plugs, then you might have bad fuel injectors on those two cylinders. That is pretty uncommon, so if you have a compression tester try testing the compression to make sure those two cylinders have good compression relative to the others.

How is your coolant level?

-Rod

[lgraham5400]

The coolant level seems ok. The car has about 95,000 miles on it.

[lgraham5400]

We changed the spark plugs, plug wires, and fuel filter but have seen very little change. There is no moisture in the oil so I do not believe we have a blown head gasket.
It runs fair at high rpm but idles very rough. Any other ideas?

[shorod]

Have you checked for good, consistent spark on cylinders 3 and 4, or checked compression?

-Rod

[lgraham5400]

I'll probably need to take it to a mechanic to check those. I don't have the equipment or the know how.