My check engine light came on. Took it to Auto Zone to get it read, comes back as cylinder 5. So two questions, how to tell which one that is? And should i change the spark plugs. It is a six cylinder, 3.0 engine, if that makes a difference. Ok three questions. If I change the spark plugs is there anything else I should do at the same time? Any advice for lady working on her truck really appreciated.

 

Ford numbers V6 engine cylinders this way
3 6
2 5
1 4
Front

V8's
4 8
3 7
2 6
1 5
front

So passenger side front to back, then drivers side front to back.

Chevy does it different, just FYI

Remove #5 spark plug and have a look at it, remove any other spark plug that is easy to get at and compare them.

Google: spark plug condition
select any of the images that come up, they tell you what spark plugs look like "normally" and with different problems.

Spark plugs have a Gap, the distance the spark needs to jump to ignite the air/fuel mix.
3.0l uses a 0.044 inch gap, these are in hundredths of an inch so fairly precise.
If you are just buying the one spark plug see if the parts place will "Gap it" for you.
If not the Gap tool is not expensive.

Spark plug is easiest thing to change if there is a misfire on cylinder #5.
But could also be the spark plug wire or fuel injector, and worst case would be a bad valve seat.


And just a heads up about the Coil Pack wires, the spark plug wires
It looks the same as the cylinder numbers, and it is for the passenger side but NOT for drivers side
Ford V6 coil pack spark plug wires are:
3 4
2 6
1 5
Front
The 5 6 4 goofs up people all the time
So your misfiring spark plug #5 is the first wire on the passenger side of the coil pack, trace it back to make sure

 

So I need to check two of those cylinders, is that correct since the wires are number different than the cylinders? All I know is what the readout from the machine said.

 

If the code was P0305(misfire #5) that means the computer has detected cylinder #5 has been misfiring over a period of time.
Computer doesn't set a code for occasional misfires, misfire has to be repeated quite a few times to get a code.

Pulling out the second spark plug is just to compare it with #5 if they look the same then spark plug is probably not the problem.

The Computer doesn't have a clue about why a cylinder misfires.
On the front of the engine behind the lower pulley, is the Crank Position(CKP) Sensor.
It "reads" a wheel, on the crankshaft, with teeth on it, each time a tooth passes by the CKP sensor it sends a pulse to the computer.
This wheel has 1 missing tooth, the missing pulse tells computer when #1 cylinder's piston is at the top.
Since it knows when #1 is at the top it can tell when 2, 3, 4, 5, and 6 are also at the top, by counting the pulses.
If you are accelerating, the computer knows each cylinder that fires will increase the speed of the wheel/pulses by XX milliseconds.
If a cylinder doesn't fire, then it will be less than XX milliseconds, so no speed added
If you are just cruising along then each pulse will be X milliseconds apart, if there is a misfire then longer time gap, less power added.

If you are decelerating then it can't detect misfires.

So P0305 is just computer saying "heads up" #5 doesn't seem to be adding the same power as the other 5 cylinders.
No specific reason, could be spark, fuel or mechanical issue, it is just a "heads up"