Skippng and misfire on cylinder # 4. How do you know if it is a fuel injector or a coilpac? Is there a way to test either or both? Since the each coilpac is for a dual cylinder should you get a dual misfire code?

P0304 is a diagnostic trouble code (DTC) for a misfire on cylinder 4. This could be caused by a variety of issues, including a faulty spark plug or oxygen sensor. However, a rough idle and a misfire could also be caused by other issues such as a vacuum leak, low fuel pressure, or a malfunctioning fuel injector. It's best to have a professional diagnose the specific cause of the issue.

p0171 is fuel injection system too lean - bank 1
possible causes
- Intake air leaks - Faulty front heated oxygen sensor - Ignition misfiring - Faulty fuel injectors - Exhaust gas leaks - Incorrect fuel pressure - Lack of fuel - Faulty Mass Air Flow (MAF) sensor - Incorrect Positive Crankcase Ventilation (PCV) hose connection
p0304 is cylinder 4 misfire detected.
possible causes
Faulty spark plug 4 - Clogged or faulty fuel injector 4 - Faulty ignition coil 4 - Fuel injector 4 harness is open or shorted - Fuel injector 4 circuit poor electrical connection - Ignition coil 4 harness is open or shorted - Ignition coil 4 circuit poor electrical connection - Insufficient cylinder 4 compression - Incorrect fuel pressure - Intake air leak
p0305 is same as above but cylinder 5.
p0306 is same as above but cylinder 6.
p0300 is random misfire detected
possible cause
Faulty spark plug (s) - Faulty ignition coil (s) - Clogged or faulty fuel injector (s) - Intake air leak - Fuel injectors harness is open or shorted - Fuel Injectors circuit poor electrical connection - Ignition coils harness is open or shorted - Ignition coils circuit poor electrical connection - Insufficient cylinders compression - Incorrect fuel pressure

you have a bad spark plug wire on cylinder 4 or your ignition coil
(coil pack) is bad.

here is a good guide to testing coils and wires if you need it
How to Test the Coil Pack Ford 3 0L 3 8L 4 0L 4 2L

The P0304 code means that the cylinder 4 is misfiring or is randomly misfiring. Start by checking for intake leaks an if no leaks are found the next step is to replace the spark plugs on cylinder 4. If the problem persist more tests needs to be done to diagnose problem, see "Possible Causes"

- Faulty spark plug 4
- Clogged or faulty fuel injector 4
- Faulty ignition coil 4
- Fuel injector 4 harness is open or shorted
- Fuel injector 4 circuit poor electrical connection
- Ignition coil 4 harness is open or shorted
- Ignition coil 4 circuit poor electrical connection
- Insufficient cylinder 4 compression
- Incorrect fuel pressure
- Intake air leak
most likely change your spark plugs these should be done every 60,000 km

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- No pulse to injectors? http://technoanswers.blogspot.com/2012/01/no-pulse-to-injectors.html
---------How to Test and Replace Fuel Injectors? http://repairhelpcenter.blogspot.com/2011/11/how-to-test-and-replace-fuel-injectors.html
---------

How to Replace a Fuel Injector
http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-injector.html
--------
Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

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Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

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Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

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Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

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This will help.

Thanks.

CHECK FUEL INJECTOR WIRING TO NUMBER 4 INJECTOR,HOOK A TEST LIGHT TO MAKE SURE IT BLINKS WHILE ENGINE RUNNING.THAT WAY YOU WILL KNOW IF PCM FIRING THE FUEL INJECTOR OR FAULT AT THE INJECTOR WIRING OR YOU HAVE INTAKE LEAK LOW COMPRESSION TO THAT CYLINDER BECAUSE OF BAD BURNED OUT VALVE.COMPRESSION TEST TO THAT CYLINDER CAN ALSO HELP.LOOK FOR LOOSE OR WORN DAMAGE ROCKER ARMS IF YOU HAVE A SOHC SINGLE OVER HEAD CAM ENGINE.

Plugs get changed at 70,000 miles
I would suggest that you use the OEM
Plugs,they are made by NGK and are special
on my 2004 LS,I don't know about yours.

Clean the MAF Sensor with the CRC Product
for that

Change the 2 front O2 Sensors at 100,000 miles

Check fuel pressure at the fuel rail on engine

The coil you replaced on #6 ,even though you
have a PO306 Code,doesn't mean that was the
bad one. It is a COP Coil or Ford thing, you will
learn as you get involved with them

In some cases, you buy 1 new coil and walk it
from one cylinder to the next.

On single coil codes, you may get lucky,on multiple
codes or a really bad coil you won't

Your not using any fancy test equipment and
unfortunately a lot of repair shops have it and
don't know how to use it,including dealers

V6 or V8 ?

P0301 - Cylinder 1 Misfire Detected.

Possible Causes:
- Improper spark plug at cylinder #1
- Insufficient compression at cylinder #1
- Incorrect fuel pressure
- The injector circuit is open or shorted at cylinder #1
- Fuel injector #1 may be faulty
- Intake air leak at cylinder

Possible Solutions:
- Perform Injector Service
- Replaced Spark Plug #1
- Replaced Injector #1
- Replaced Ignition Coil #1

Being you have a heavy gas smell I would look into the injectors. If injector #1 is over producing it can cause a misfire. Test your compression and fuel pressure.

That's a good starting point. Make sure the injector electrically working (getting signal to fire) If so take a fuel pressure test to see if the fuel psi is within spec. If not (high psi) the injector is probably your cause. (usually not firing, electrical)

Hello
Here is what to check let me know if you need help checking this out
most common misfire causes on the cars I've worked on have been:

1. Spark plugs
2. Spark plug wires
3. Ignition coil
4. Fuel injector
5. Wiring to fuel injector
6. Timing Belt
7. Vacuum leak or stuck open EGR
8. Contaminated fuel or bad fuel pump
9. Weak compression
10. Blown head gasket