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Discussion Starter #1
I have a 1997 Grand Marquis. It had a misfire a few months ago in cylinder #5. I changed all plugs, and saw there was oil on the plug, above the seal. That is, it must have benn in the spark plug well. There was no oil on the threads, or the electrode.

The misfire went away,

Then two days ago, I started getting a backfire, from near the engine compartment, and a slightly stumbling idle.

Pulled plug #5, and there was oil on it again. (see picture). I cleaned it, and the backfire stopped.

Two days later I noticed a slight stumble, and pulled the plug, and the oil was there again.

I am assuming the misfire (two months ago), and the current backfire, and stumble, are related to this #5 plug. I did see a misfire code tow months ago, but as threre was not misfire (yet, anyway) for this plug this time.
Where is oil coming from? valve cover?


This is the clean plug:
spark plug 1.jpg

This is the oiled plug:

spark plug 3.jpg

spark plug 2.jpg

This is a picture of the plug pars (roughly the same as mine, the oil is above the area labeled 'SEAL SURFACE'):
spark_plug parts.jpg

The spark plug hole is NOT in the valve cover:
https://www.fordforums.com/attachment.php?attachmentid=50198&stc=1&d=1547784316
 

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Discussion Starter #2
(BTW, I've had P430, O2 sensor below threshold for over a year now, but think that is not the cause of either the misfire, backfire, or stumbling).
 

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Its more likely coolant coming from the intake manifold. The gaskets on my 02 gt were leaking and got nasty coolant in the spark plug wells of cylinders 5,6 and 7.
 

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The oil on plug body can cause the spark to track which will give intermittent misfire . Check for any oil leaks , possibly from valve covers. Always better to to replace boots and apply dielectric grease .
 

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Discussion Starter #5
Where is the dielectic grease applied? Around the plug? Around the boot? All over the boot, or just near the top of the boot to keep oil out?
 

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I was thinking it was oil based on the color.

I suppose it could be coolant, that was made dark from dirt and grime on the engine?

How could I test to distinguish if it's oil, versus coolant?

I am also adding 1 quart every 600 to 800 miles, so the oil is being lost somewhere, although I was guessing mostly it was from a bad seal around the oil pan...

I also add a small amount of coolant (about 1/4" in the coolant reservoir, every 6 months).
 

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Where is the dielectic grease applied? Around the plug? Around the boot? All over the boot, or just near the top of the boot to keep oil out?
Just put a dab inside the end of the boot that slides over the plug. Doesn't take much.
 

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You can smell it, coolant will have a distinct smell. And most likely the valve stem seals are bad allowing oil into the chambers and its burning the oil. Bad valve stem seals are a common problem for 97- 4.6 2v motors.
 

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Discussion Starter #11
Well, I tried smelling the fluid, and I can't say for sure it smelled like either coolant, or oil to me. I'll try again later.

As far as symptoms you mentioned of bad valve stem seals - I am not seeing blue smoke. I don't know how to view the carbon on the valves, since they are in the block? I also am not seeing any wetness on the spark plugs electrode tip. All the wetness is above the spark plug's sealing surface, so I think it must be entering from the top of the spark plug well. Which makes me think it's not bad valve stem seals - as that seem like it would show wetness on the spark plug at, or below, the spark plug threads.

I just did a little research, and saw that the intake manifolds on these cars are prone to eventually leaking and breaking, at the coolant crossover part of the intake manifold. So, now I am worried that the intake manifold might be starting to leak on mine.

I have a few more pictures that I've put into a shared album on Google Photos, that you can look at here, and maybe you can see something I am missing...

On my Google Photos link, you can click on a single picture, and it will open up and be enlarged. Then on that phot you can enlarge it even more by using your mouse's scroll wheel (or clicking on the magnifying glass icon, which is in the upper right hand corner of the screen). When enlarging the pictures that show the engine, spark plug wells, and what I think is the edges of the intake manifold - I think I see what might be coolant near the intake manifold. But it's hard to tell. Do you have any impressions of what is there?

https://photos.app.goo.gl/dpDjp3fGaQ9Pombn7
 

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You DONT have any of the symptoms of valve stem oil seals failing . Rather than guess and do any unnecessary work , clean about the area of the plug , run car and see exactly where the oil on plug is coming from .
 

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Discussion Starter #13
Good idea to clean and observe.

Would spraying carb cleaner, or some other cleaner(not sure what to try, do you have a suggestion?), around that spark plug hole be a good way to clean up that area? Would that damage the spark plug boot, or other seals, hoses, or electronics if I spray onto them by accident?

Did you happen to look at the pictures I linked to in my google photos? I'm just wondering if you also found it hard to determine what the leak is?

(I have about 6 inches of snow to clear today. Here in Michigan. So I may not get to this cleaining for a day or so.)
 

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I've used carb cleaner , brake cleaner and others many a time and never really had any problems with doing so .Obviously dont go crazy especially near any electrics . Most evaporates and residue can be mopped up with paper towels or cloths . Once cleaned , you can use leak tracing powder or even talc powder in that area and you should see route oil is coming from onto plug.
 

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That looks like coolant to me. It has a greenish tint in some of the pics. Clean up like Logan said and watch for new leaks.
 

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Discussion Starter #17
Thanks all for your input. i'll try cleaning and observing.

I was wondering, would it be a good idea to try to tighten down the valve cover bolts, or the upper manifold bolts? Could the manifold crack if I over tighten those bolts?
 

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If its coolant and the intake isnt cracked then its probably coming from the manifold gaskets. They can shrink with age and allow seepage especially if it sits a lot. I wouldnt recommend tightening the intake more unless you use a torque wrench and it isnt torqued to spec.
 

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Wouldn't do any harm if you " nipped " valve cover bolts but usually gaskets can harden / lose sealing capabilities over the years and need replacing as the only answer but don't overdo or you will make matters worse .
 

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