onlyexilove
Full Access Members
So I think I finally fixed my constant misfire and rough idle after messing with it and throwing about $1000 at it over the last 3 months.
I had the famous P0304 code that I could not get rid of and that didn't always pop up right away. I started my journey with swapping the plugs, COP's, all 4 O2 sensors, the computer (based on what Ford thought it was) and still had the same code and issue pop up. I checked the fuel pressure and all looked good with it, Ford also did a compression test and it came back great. I checked through every thread on this forum and others and found out that typical issues for the 5.4 motors (also including the 4.6) is that the intake gasket goes bad causing coolant to leak internally and blow out the spark on the #4 plug. This also looks bone dry from under the hood. So I went this past weekend and pulled the intake to find that it had been leaking both coolant into the port and oil down into the valley between the heads. I also found that the connector for the #4 COP had a broken rubber gasket/ o-ring internally on the connector causing the COP to not have a proper connection. I also went ahead and swapped out my fuel filter since I don't ever remember seeing service records for that being done by the previous owner. After putting everything back together and taking it for a test drive, my idle has gone back to normal, I have more power, no misfire code (as of yet), and no popping sound coming from my exhaust. The biggest bonus is that my wife is really happy with her Expy again
So to recap what all was replaced and what I would recommend doing first:
Spark Plugs
COP's
O2 sensors (all 4)
Computer
Intake Gasket
Fuel Injector O-rings (on all injectors)
Oil Change
Coolant
Fuel Filter
My recommendation would be to first check the gasket for your intake and see what it looks like. More than likely you will see something in the valley between the heads. Also thoroughly check your wire connector ends and the internal rubber o-ring gaskets to ensure they are properly seating on the COP. I would then start looking into the other parts afterwards since they are typical major tune up items anyway.
I hope this helps with the notorious P0304 misfire code for the next person that gets to deal with it. Please feel free to PM me with any questions you might have.
I had the famous P0304 code that I could not get rid of and that didn't always pop up right away. I started my journey with swapping the plugs, COP's, all 4 O2 sensors, the computer (based on what Ford thought it was) and still had the same code and issue pop up. I checked the fuel pressure and all looked good with it, Ford also did a compression test and it came back great. I checked through every thread on this forum and others and found out that typical issues for the 5.4 motors (also including the 4.6) is that the intake gasket goes bad causing coolant to leak internally and blow out the spark on the #4 plug. This also looks bone dry from under the hood. So I went this past weekend and pulled the intake to find that it had been leaking both coolant into the port and oil down into the valley between the heads. I also found that the connector for the #4 COP had a broken rubber gasket/ o-ring internally on the connector causing the COP to not have a proper connection. I also went ahead and swapped out my fuel filter since I don't ever remember seeing service records for that being done by the previous owner. After putting everything back together and taking it for a test drive, my idle has gone back to normal, I have more power, no misfire code (as of yet), and no popping sound coming from my exhaust. The biggest bonus is that my wife is really happy with her Expy again
So to recap what all was replaced and what I would recommend doing first:
Spark Plugs
COP's
O2 sensors (all 4)
Computer
Intake Gasket
Fuel Injector O-rings (on all injectors)
Oil Change
Coolant
Fuel Filter
My recommendation would be to first check the gasket for your intake and see what it looks like. More than likely you will see something in the valley between the heads. Also thoroughly check your wire connector ends and the internal rubber o-ring gaskets to ensure they are properly seating on the COP. I would then start looking into the other parts afterwards since they are typical major tune up items anyway.
I hope this helps with the notorious P0304 misfire code for the next person that gets to deal with it. Please feel free to PM me with any questions you might have.
