P0303 Code, Where to Start??

[buzz]

2000 XLS, 4.0. Just got the P0303 code-generic misfire cyl 3- with noticeable rough idle. Engine has 62,000 easy miles on it, maintained, etc.

Should I replace cyl 3 plug and swap the wires, clear code? Anything else to check?

 

[Tbars4]

...Is it a P0303 code?

..Swap the wire with another cylinder then the plug and see if the code changes after about 50 miles each with the swap..

 

[buzz]

...Is it a P0303 code?

..Swap the wire with another cylinder then the plug and see if the code changes after about 50 miles each with the swap..

Yes, P0303. Will do.

Do you know what the average life is for the OEM plugs and wires?

 

[Tbars4]

..I believe maintenance is about 75k miles but there are lot's of variables so judging if a wire or plug should be changed upon only a number would not be realistic.

 

[jremington59]

A code P0303 may mean that one or more of the following has happened:

•Faulty spark plug or wire
•Faulty coil (pack)
•Faulty oxygen sensor(s)
•Faulty fuel injector
•Burned exhaust valve
•Faulty catalytic converter(s)
•Running out of fuel
•Poor compression
•Defective computer

 

[rs2k]

A good way to check the wires is look under the hood in the middle of the night. You can often see the sparks or sometimes even your bad wires will glow. It's not a conclusive check, but it'll sure tell you they're bad if you see them glow or arch.

 

[buzz]

I pulled the plug. It definitely looks different than one from a good cylinder. Anyone know why the threads are rusty/dirty? Does this tell you anything about the cylinder? Thanks.

Bad

Good

 

[rs2k]

That plug looks good other than the fact it's worn out and the threads are dirty. Just looks like corrosion on the threads.

 

[2000StreetRod]

threads stripped?

It looks to me that either the plug was not screwed in all the way or the last six threads in the head are stripped. Only the first four threads of the plug have grooves indicating matching threads in the head.