Plug Fouling w/ pics - Rebuild Time?

[RammaR]

I have the 4.0 OHV engine in my '96 XLT. Its at 170,000 miles now and has held up pretty well. However last summer I had a mis-fire in cylinder #3. I pulled the plug and it looked pretty nasty, and smelled funky. The parts store said it might be water fouling for the smell.

I did a compression test and cylinders #3 and #4 were down a little bit from the others (~140 psi vs 150psi). That was with the engine cold and I did't have a good way to add a little oil into the cylinders to check if the compression came back. But that difference was less than 10% so I didn't think too much of it.

Now a couple weeks ago I had a mis-fire in #4, when I pulled it it was fouled with a dark wet fluid. I thought it might have been oil, but it smelt like gas and mostly evaporated over night. When I discovered that cylinders #3 and #4 are tied to the same block on the ignition coil I decided to check it. The
secondary resistance was a little out of range, so yesterday I put on a new motorcraft ignition coil, wires and plugs.

When I pulled the plug from #3, the plug threads looked really dark and oily again. Like it was only a matter of time before it fouled:

The firing gap looks pretty good and clean but the threads are nasty. So I thought it might be a valve cover leak running down on the outside. Here is a picture of the socket -- no oil is leaking down from the valve cover, but you can see a small thick puddle at the bottom of the socket.

The two week old plug in cylinder #4 also looked similar - already showing signs of oil while the gap looked brand new. It really doesn't seem to use any oil, and there are no leaks of any kind on the garage floor. But it has been using some coolant lately, but that wouldn't look like this in the pictures would it?

Both of these cylinders are a little low in compression, does it sound more like a head problem or failing rings? Is there something else I can check to pin down the issue further?

Thanks for the help!

 

[RammaR]

Looking at it some more, the oil / crud on the plug looks like its being blown out past the threads and not leaking down from the outside. I used a thread sealant / anti-sieze this time around.

But I still think I've got another issue going on inside because of the fouling. Any suggestions on what to check next?

 

[cybergasm]

some ideas for ya

The parts store said it might be water fouling for the smell.

If this is the case then i would say it's probaly failing head gaskets. that about the only way for water to enter the cylinder the other possiblility would be a cracked cylinder wall. If you got access to a block checker kit then I would try that to see if gas is entering into the coolant or maybe try a leak down test if ya got the equipment.

 

[RammaR]

I don't have a block checker, but could swing by a parts store and probably rent one of the coolant pressure testers. The oil looks clean and isn't being burned, so I think that's sorta a good sign.

One post said to remove the radiator cap and run the engine hard to see if it bubbles up and out. I think to check for a cracked head. There was another post about the lower intake manifold being the source of coolant leaks and plug fouling -- that would certainly be easier to replace. But is there any way to determime which is it before tearing into the motor?

 

[RammaR]

Last night I removed the radiator cap and gunned the engine a few times to see if the coolant would 'puke' out -- it did not. The level slowly rose to the point it started to overflow, but it didn't bubble or errupt.

It idles great with the new plugs, wires and ignition. But I know in a few months I will have fouled plugs again. I guess I should try the coolant pressure test and maybe another compression test.

 

[Bigg_billy]

With that many miles you are bound to be burning a little oil. Another condition that sometimes happens is when you shut off the engine a little fuel may continue to drain out of the lines into the cylinder, thus helping foul out the plug earlier than normal. Whether or not the fuel pressure regulator is at fault or not I'm not sure. If the plugs foul out though, the heads and piston tops might be covered with the same carbon build up. Get some NAPA Sea Foam treatment and follow the directions, basically dumping the can down the TB stalling out the engine, let it sit a half hour and then fire it up. If you see a giant smoke screen coming out of the exhaust you have accomplished something and cleaned up your upper end. When I say smoke I mean smoke, it will get the neighbors wondering if it's on fire. Let it warm up and your off, clean.

Bill