I have a 1999 F150 5.4L. I have recently experienced some misfires, rough idle, etc. The code that I have pulled was the P0304, misfire on #4. I changed out the COP and cleared the code. Just a few days later, my truck started acting up again and I pulled the same code. I have a brand new COP on it and have read some other posts in regards to the P0304 code. One of the posts that I read stated something about some black brittle plastic that was pulled from around the exhaust manifold that came from somewhere. I also pulled the same black brittle plastic from the same area. I have no clue what it is, but would really like to know. In the same thread, somebody had replied that the misfire was more than likely caused by a vacuum leak and the PCV hose should be checked at the back of the throttle body. There is also a smell of gas when I start the truck.

Now, I am not really to mechanically savvy. Where is the throttle body and what opinions do you all have in regards to this? Any info any of you might be able to give will be greatly appreciated!

 

Hello there. The throttle body is located under the hood under the cover that says 5.4L on top of it. Remove the three 10mm bolts. Then you can remove the intake elbow that is attached to the throttle body. If you want you can go to a local parts store and buy a repair manual for less than $20. It will help with some of your questions also.

 

So what might the smell of gas be caused by?

 

Well the smell of gas is likely unburned fuel. Your cat convert is intended to burn off excess fuel but can only do it within reason. My truck too smelled like gas and I had a code stating a misfire in #6. I have since changed the plug. the gas smell is gone, and it runs much smoother at Idle. I do however have some rough acceleration. I have, wries..so I am going to swap them today.

When I do that, I will check some of the vaccum lines too.

Your posts was misleading, so forgive me if this is not what you were asking.
The throttle body is a new age carburetor. If you follow the tube that houses your air filter towards the top of the engine...you'll come right too it.
Now I have a 4.6 liter. Now assuming the set up is the same, when you remove the tube from the front of the trottle body....there are going to be a few addtional rubber hoses underneath. One of the hoses snakes around the the drivers side valve cover which houses the PCV valve.(positive crankcase ventilation) The hose was stuck pretty well , so if it was removed several times over the life of the truck...it may have encountered some strain and cracked. Cracks can be hard to find. I try and remove the hose and put a bit of compressed air in one end with my finger covering the other and feel for air in through out the hose. You can also submerge the hose in a bucket of water while doing and look for bubbles. (Works o.k for me)
Again, this is on the 4.6 now somebody said the rear of the throttle body for a 5.4. If this is true....it is the same idea as I described just look at the PCV and follow it back towards the throttle body.
I've also heard a lot of guys here talking about cleaning the EGR valve. Apparently that builds up quite a bit of carbon. Not too sure if that would cause your symptoms....maybe somebody else here could chime in on that.

 

The pcv line your asking about goes from the pcv valve to the back of the intake. The elbow at the intake is prone to breaking. The line & new pcv can be bought from Ford for about $20. Look at the rear of your intake by the firewall. Just follow the line from the pcv to the intake. I've put 2 on my truck & both broke at the elbow at the intake.