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Old 03-26-2012, 09:38 PM
olddog olddog is offline
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2001 Ford 4.6 ltr Plugs

My 01 Grand Marque has 120K miles on it, with original plugs. For about the last year or so, it would miss every now and then. It has been getting worse over time. It may not do it for several weeks then it may start missing (a cylinder dropping out). If you step down on the go peddle it will quit.

So I bought a set of plugs and boots for the coils (coil on plug). The boots also had new springs. This car collects more dirt under the hood than my vacuum sweeper can suck up in a year. So I stopped at a car wash and sprayed the engine and under hood, with the cover off the top of the engine. I especially sprayed the plug area so there would not be any dirt to drop into the hole. I wondered if it would start, especially if it had a bad boot. No problem, it started and ran normally.

A few days later the week end came and I started the job. When I pulled the coils off, one coil next to the oil fill tube had a touch of oil in the hole. I expect someone may have spilled some oil no big deal. When I got to the coil in the back on the passenger side (think #4 - I cannot remember which side is which at the moment) it was full of oil. With coil removed the oil was almost to the top of the plug. About where the electrode meets the porcelain. Note oil fill is on the drivers side; no reason oil should have ever spilled near this plug.

Boots and springs were in good shape, but since I had new I replaced them anyway. I measured the resistance of all coils (both primary and secondary). Primaries were all the same +/- 1 and secondaries were identical. I used compressed air and a rag, with carb cleaner to get all the oil out. Changed the plugs and put it back together.

Runs like a top. No misses. I assume the oil was causing the miss? Yes/No?

This car has always been garaged. There has never been a drip of oil on the floor. I do not think it has a valve cover leaking, but since I sprayed it off, I cannot be certain. Also if the boot was letting oil in, there should have been water in it, especially at high pressure. Could the head be porous or have a crack or pin hole leaking oil into the spark plug tunnel?

Any experience or thoughts as to how the oil got there?

Last edited by olddog; 03-26-2012 at 09:47 PM.
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Old 03-26-2012, 11:25 PM
thcardoc thcardoc is offline
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Valve cover seal leaks are common on these. That oil getting on the plugs and boots does cause misfires to occcur. The question comes down to how fast will it occur again? Replacing the valve cover gasket and the plug well seals right now would be adviseable. But it could take a couple years before the oil builds up enough to cause you any trouble.
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Old 03-27-2012, 08:47 AM
dougbfresh dougbfresh is offline
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Probably lucky you didn't try to yank the plugs, I think this is the one that the plug disentregrates when you try to remove them. I think they are the 2 piece design, heard many stories about having to yank the heads to get the remnants of the plugs out.
http://www.bing.com/search?q=4.6+lit...c=IE-SearchBox
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Old 03-28-2012, 10:39 PM
olddog olddog is offline
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Quote:
Originally Posted by dougbfresh View Post
Probably lucky you didn't try to yank the plugs, I think this is the one that the plug disentregrates when you try to remove them. I think they are the 2 piece design, heard many stories about having to yank the heads to get the remnants of the plugs out.
http://www.bing.com/search?q=4.6+lit...c=IE-SearchBox
This 2001 has regular plugs. I know the 03 has the two piece plugs. No sure about the 02.

Anyway the plugs are changed.
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Old 03-28-2012, 10:47 PM
olddog olddog is offline
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Quote:
Originally Posted by thcardoc View Post
Valve cover seal leaks are common on these. That oil getting on the plugs and boots does cause misfires to occcur. The question comes down to how fast will it occur again? Replacing the valve cover gasket and the plug well seals right now would be adviseable. But it could take a couple years before the oil builds up enough to cause you any trouble.
I did replace the boots, which are what seals the tube. I will watch the valve cover for a leak, and replace them if they are leaking.

If they are not leaking, then the tube itself may have a leak. If it takes another 10 years to fill up, I'll be done with the car. If it causes problems sooner, I may try to sleeve it with a thin wall tube. I hope not.
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