HAVE 99 5.4, engine miss. sometimes worse than others. If i start and miss is bad i turn off and start again and runs better but not great. changed fuel filter,air filter,IAC, dont know what to try next. code says 4 possibilities: bad rings not, fuel injector,or lg vac leak. changed vac hoses. need help!

 

Change the PCV valve. It's a $3 items and could be at least part of the problem. Inspect that hose that goes to valve for damage and leaks. Do you have a check engine light indications and have you pulled the codes? Would also check your EGR valve. it should move freely and they tend to get dirty and stuck. If sticking, you need to take it off and clean it with wire brush. Also, the pipe that goes from the manifold to the EGR can get clogged and cause problems. Inspect it when you take off the EGR.

I cannot tell from your post but you may have a miss from something as simple as a bad spark plug. If this is happening you should be getting a check engine light.

 

changed pcv valve and hoses never checked egr but will try next. As far as plugs i changed them and coil packs 6 mos. ago. As i said it runs good sometimes and bad so i would think if it were plugs it would be bad all the time. Thanks for ur help.

 

Also cats were removed 6 yrs ago so light stays on from o2 sensors. p0304 code for #4 cyl. always there even after tune up. prob rings but was running fine till just recently .

 

check heat range on your spark plugs. im using bosch and they are horrible on cold starts.

 

Sorry for not responding sooner but after reading all the issues from your truck, I strongly suspect you are leaking coolant from the heater hose quick disconnect fittings that are just above and a little to the left of your number 4 plug. The coolant has been known to flow into the number four plug socket, turn to steam, and short out the plug. this explains why is runs good sometimes and bad at other times. It usually runs fine after you put in an new plug or clean the old one and then starts running bad again. It only need to leak a little to cause your problem.

Here is what the quick disconnects look like. To remove, you push in the tabs of the inner connecter piece and pull everything off. To install, you assemble all parts of the connector and push it on the heater port. A little grease or oil on the port helps it slide on easier and seals the o rings. If the outer brackets of the disconnect are cracked or broken, they won't hold the hoses tight and they will start leaking. The hoses cost about $30 each and are pretty easy to change. picture of disconnect is here http://www.f150online.com/galleries/...3442-87148.jpg

http://www.f150online.com/galleries/...3442-87148.jpg

 

Sir, u are a genius. Thanks for the help. I've been scratching my head for 6 mos.