Hello All,

I'm new here. So hopefully I am posting in the correct thread. Here we go...

I have recently been getting the code P0304 on my 99 Ford Expedition 5.4L. This isn't the 1 or 3rd time I've received this code. It seems to only occur after it has rained really heavy here in Missouri. Now I've replaced the #4 cylinder coil a number of times and the service engine soon light and the shaking normally clears.
Well this time I also replaced the spark plug in hopes the issue would stay gone. The service engine soon light is gone but the truck is shaking still. Seems to be now an idling issue when I'm in Drive.

I don't notice any accelerating issues or shaking when the truck is in motion. Just when I'm in drive with my foot on the brake.

I'm wondering if the spark plug isn't secure all the way?
Or the cylinder coil is bad?

Hopefully I don't have to replaced the other 7.

Now I'm thinking maybe the IAC is needing to be replaced.

I'm no guru by any means but I do a lot of the work myself if I think it is something I can do. So far so good. but now I'm a bit stuck. Any help, opinions and or suggestions would be much appreciated.

Thanks.

 

Leave the IAC alone. What plug did you put in? Was it a factory platinum plug or did you cheap out and get a standard plug? (not judging, but it really matters a lot) Also, an injector will also cause a miss. Not every miss is ignition. It could also be fuel. 5.4Ls are bad for eating cams, I would also do a compression check. .....go back to the basics. Check all the standard stuff and find your weak spot.

 

Hello,
Thanks for the reply. I used the Accel Super Coil from Advance Auto Parts. Later this week I will look to do a compression check. I will also recheck the coil and spark plug make sure it is secure. I appreciate the help. I'll let you know what I find.

 

Luckily all I have had to change is coil pack's and some of them more than once. But at least the ones needing changed more than once were under warranty.

 

Well seems I had another coil go bad on me.
I went out to the old beast earlier today and did some looking and everything seemed to be connected just fine. I unhooked the battery for about 5 mins and hooked it back up. I let the engine run for about 10 - 15 mins. Then the service engine light came on. Code p0303 popped up. Seems that one went bad. I replaced that ignition coil and spark plug as well. Now she runs good and there is no rough idle. I'm guessing it's time to replaced the other 6 here soon..

 

It would not hurt to go thru all your under hood connections and make sure they are corrosion free (clean them with that electronic cleaning spray) and then put some dielectric grease on the connections.

At least you found it, hope it was not the R/H aft plug..PITA

 

That's not a bad idea. I will get that done as well. I'll have to go to AutoZone to get some digrease. I'm happy it was a fairly easy fix. Wish they all were.

Not sure what a R/H aft plug is.

 

Meaning did you have any issue replacing the (R/H) right hand aft or rear spark plug? I remember it being hard to reach...?

 

The #4 Coil and Spark plug is a bitch to get too. Truly a bitch being that it is so far back toward the firewall. But I was able to do it. The #3 isn't that difficult but still a pain to get to. I'm not looking forward to replacing 7 and 8.

 

Check your heater hose connections. They're right over #4 and #3 coils. Get a leak there and it shorts them out.