first of all i have browsing the forums the last 2 days looking for insight on the issues on my 2002 f150xl 168,000 miles. thanks for the help.

 

Welcome to the site. If you need anything specific, just ask.

 

been try to find fix to codes po171 po174 running lean po303 po316 missfire on#3 cyl. repaced plug wires and plugs #3 plug had heavy carbon. checked for vaccum leaks by spraying carb cleaner at all vac hoses. no change in idle.
there is no miss at idle. only on acceleration. also checked egr fine. thanks for any input 4.2L engine

 

Did you check the PCV elbow behind the intake manifold?

 

checked it as far as spraying wd40 all around it,no change in the idle.
it runs fine at idle when i start to drive it begins to missfire. if the coil pack was bad wouldn't it continue to missfire at idle?

 

4.2 is on the side of the throttle body isn't it?

171 &174 can be a booger sometimes, check for ANY possible air leaks after the MAF even the intake tube to the t/b, it could be split/cracked.
Also on the PCV the O-ring where it goes into the t/b and the 2 rubber hoses at either end of the plastic pipe to the valve cover.
It can also be caused from an exhaust leak closr to the O2 sensors.
Or the all famous Plenum gaskets and Isolator bolts (that is what mine was).
You are searching the V-6 forum right? With the search function?

 

how many pcv on 4.2L I see one left rear valve cover and right front of valve cover

 

seaching v6 section. thanks for your replies.
why only the misfire on #3

 

PCV line is on passenger side valve cover towards the back. There is a little rubber hose that connects it to the elbow in the valve cover-it can go soft and leak.
Also the other 2 lines, the small ones, are coolant lines on the PCV-make sure the system is cool or NO pressure before you remove them.

The line on the driver side is for "intake" for the crank case so when the PCV sucks air into the intake it doesn't create a vacuum in the engine.

The #3 misfire could be several things.
Bad wire
Bad plug
Clogged/leaking injector
Bad valve (not likely)
Bad coil pack (cracked or weird ground)

Alot of things can cause a misfire.

 

when i pulled the #3 plug lots carbon on it. the rest seemed fine only 30k on plugs

 

What color?

 

black?

 

Most likely oil. Could be bad rings or valve guide seal.
You could do a compression test (wet and dry) that would tell you if it's rings or guide.
If you compressoin test check all the cylinders on that side and post what you got.

 

didnt look like oil and wasnt wet

 

ive read many of your posts and find them quite helpful thanks. saying that im an idiot for driving 50k with the po171 po174 codes there. it was running fine till a few days ago the missfire on3 began po303. im ready to pull off plenum and replace iso bolt as you suggested on other posts for same issue.