#4 spark plug oils up
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Freshman User
Joined: Dec 2002
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#4 spark plug oils up
I have a 99 F150 4.6L engine that starting running rough. Check engine light starting flashing. Checked code (PO304). Removed and replaced spark plug on cylinder 4 and coil pack for that side (not COP, doesn't use that type). Also checked compression and it read 150 across the board. Ran for a little while but started doing the same thing again. Pulled the spark plug again and there was oil on it again. Spark plug threads in and out fine and tightens up fine. Checked to see if plug was loose and it was tight. Was told that oiling the spark plug could be a ring, crack in the head, or a valve stem oil seal. Could some one give me some information on what could be the cause before I either strip down my engine or replace it.
Laughing Gas
Joined: Mar 2002
Posts: 1,060
Likes: 12
From: arizona
#4 spark plug boot is hard to get to, making it easy to damage the wire.
You almost have to use a "spark plug boot" remover and grab just above where the boot intersects the head, otherwise you will be buying new wires.
Also, Whenever I change wires.....I keep some of the old wires that are know to be good so that I can swap them out if one of the new wires seem faulty.
I bet your problem is a bad wire.
(make sure the boot "snaps" on and you can feel that snap).
It's gotten me a couple of times.
You almost have to use a "spark plug boot" remover and grab just above where the boot intersects the head, otherwise you will be buying new wires.
Also, Whenever I change wires.....I keep some of the old wires that are know to be good so that I can swap them out if one of the new wires seem faulty.
I bet your problem is a bad wire.
(make sure the boot "snaps" on and you can feel that snap).
It's gotten me a couple of times.
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Freshman User
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Not meaning to sound rude, but maybe I'm not being clear enough. I want to know why my spark plug #4 keeps getting oil on it on both the threads and just below the boot. It is misfiring because of the oil fouling the plug. It is not leaking from the top pan, or anywhere else that I can see. I keep my truck well maintained (oil changes, tune-ups, etc.). I do appreciate all and any help.
Thanks
Thanks
Senior User
Joined: Feb 2010
Posts: 226
Likes: 1
From: TX
Its in human nature that we just go off in outer space when asked a ?.
A spark plug that is coated with black goop, thats oil.
If its just a brown or tan color on the porcelain, thats fairly normal.
Anyhow, if it really looks to be oil...
Its either bad valve guides letting oil seep down the valve stems when
the engine is off, or bad rings that are letting oil blow by into the combustion chamber during use.
If you notice bluish smoke upon startup, its the guides in the heads.
If you notice bluish smoke or smell burning oil while driving, its the rings.
All this can be tested using a compression tester and do a leak down test
in each cylinder. Not just a static compression test.
A spark plug that is coated with black goop, thats oil.
If its just a brown or tan color on the porcelain, thats fairly normal.
Anyhow, if it really looks to be oil...
Its either bad valve guides letting oil seep down the valve stems when
the engine is off, or bad rings that are letting oil blow by into the combustion chamber during use.
If you notice bluish smoke upon startup, its the guides in the heads.
If you notice bluish smoke or smell burning oil while driving, its the rings.
All this can be tested using a compression tester and do a leak down test
in each cylinder. Not just a static compression test.
Laughing Gas
Joined: Mar 2002
Posts: 1,060
Likes: 12
From: arizona
guitar_god2003
Does the engine still run rough AFTER you clean the plug?
If it does then I would at least check the wire.
Does the engine still run rough AFTER you clean the plug?
If it does then I would at least check the wire.
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Senior User
Joined: Feb 2010
Posts: 226
Likes: 1
From: TX
Just wondering if you checked my last reply?
This will determine why you are getting oil in the cylinder,
in the first place.
Come to think of it, check your PCV valve too in the passenger
side valve cover.
You could be sucking excess oil up into the intake.
This will determine why you are getting oil in the cylinder,
in the first place.
Come to think of it, check your PCV valve too in the passenger
side valve cover.
You could be sucking excess oil up into the intake.
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Sorry I didn't reply to your last. There seems to be a small puff of blue smoke when I first start it up but goes away after a couple of seconds. The valve guides must be bad. I did a compression test and it was fine. How do you confirm that it is the valve guides. How do you do a leak down test?
Senior User
Joined: Feb 2010
Posts: 226
Likes: 1
From: TX
Since you say that it smokes upon start up and then goes away...
the valve guides are your problem.
You dont have to do a leak down test at this point since you
visually see the blue smoke on start up. But, any good mechanic
can do a 'leak down' test fairly cheaply, just to comfirm.
Being the valve guides are going bad, you are leaking oil down the
valve shafts after you turn off the engine. It then collects in the
cylinder and burns off upon start up.
You might as well do a complete upper end at this point.
In other words, not just replacing the valve guides, but also doing
a valve job, cleaning the heads and all the other normal wear items
while you have the heads off of the vehicle.
It should/will cost anywhere from $500-$700 total.
the valve guides are your problem.
You dont have to do a leak down test at this point since you
visually see the blue smoke on start up. But, any good mechanic
can do a 'leak down' test fairly cheaply, just to comfirm.
Being the valve guides are going bad, you are leaking oil down the
valve shafts after you turn off the engine. It then collects in the
cylinder and burns off upon start up.
You might as well do a complete upper end at this point.
In other words, not just replacing the valve guides, but also doing
a valve job, cleaning the heads and all the other normal wear items
while you have the heads off of the vehicle.
It should/will cost anywhere from $500-$700 total.
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