bluekim7

Hi guys,
I am new to the forum.
My truck is a 2003 f150 with a 5.4 engine. It has a misfire on cylinder 4 and I cannot figure out the problem. It first started out this winter and would idle rough for abotu 30 seconds when started cold, after that it smoothed out and ran great. It eventually got worse this spring and started to do it everytime I started it. Now it has a misfire on cylinder 4 all the time and through the comlete RPM range.

I have done several things without an progress.

1. replaced coil and plug. Plug appears to be burning pretty good. Not wet at all. Could of had a slight whitish residue on part of the plug.
2. Swapped fuel injector from cylinder 1 and cylinder 4.
3. Checked compression and got 140 PSI.
4. Swapped coils around between 2 and 4.
5. Disconnected coil connector and truck ran much worse.
6. Disconnected fuel injector connector and truck ran much worse.
7. Pulled out PCV and truck did not idle any different or in the rpm range
8. checked hoses for vacuum leak and could not find any visually or by wiggling hoses around.


From here I am lost and don't know what else to do. If you guys have any ideas please let me know.

Thanks,
Kim

C Denny Run*

Cam position sensor(CPS) maybe?

westtnfx4

Vaccume leak somewhere....have you checked the whole system?

bluekim7

I have not had the system checked for a vacuum leaks. Can I do that myself or do I need to take it to a mechanic? I would like to avoid the dealership if possible.

Thanks,
Kim

westtnfx4

You can get a can of carb cleaner in a can and spray around everywhere...it will stall the engine if you have one....be carfull tho and don't start anything on fire please.

bluekim7

Thanks, I will try that tomorrow night and post what I find.

torkum

What was the exact code you got? Could be a wiring issue to the COP.

drof 1

A vacuum guage/fuel pressure guage is not expensive & easy to use. I believe you should get a reading of 18 to 22 lbs, steady.
If code is saying # 4 misfire though I don;t believe it is vacuum, but stranger things have happened.
Also a stethoscope is only about $8 at autozone or advance auto. Not as good as a vacuum guage.
Have you checked your fuel injector?

drof 1

After my previous post I came back to see what you had done, guess I should have first huh?
But you mention no difference when you pulled out the pcv. did you remove the pcv from the vacuum hose to see if you have good vacuum on the hose?
What does your check engine light code read? the actual code?

bluekim7

I belive the code is P304 or PO304. I will find out today on my lunch at autozone.