[Mook]

I changed my plugs and wires about a month and half ago, I noticed that the plug on the drivers side closest to the firewall was really fouled. I checked the plug yesterday and that same plug was fouled already.......anyone know why? I did notice the valve cover was a little lose at the screws and that there was a trace of oil that had run down towards the plug. The car is a stock 400, 69 GTO...thanks

[Schurkey]

Gas fouled? Oil fouled?

That cylinder burns oil?
That terminal in the distributor cap shorting to ground?
Bad plug wire?
Poor tool access for that plug, so the porcelain gets cracked when tightened?

[Mook]

OK, don't think that the plug is cracked but I will buy a new one, did tighten up the valve cover. Will switch wire with another to see if it has a short. I will also replace distr. cap and rotor.....thanks for your input.

[slowgto]

Do one thing at a time, so you know what was wrong.

Try hooking your timing light up to the bad cylinder. I expect you will see a poor, inconsistent flash, or no light, when you point it at your timing mark.

I would then swap out the wire first, and test it again. Then try the plug, cap.

[Malky]

mook, it is pretty easy to tell if it is gas-fouled because of erratic ignition or oil-fouled because of a bad valve guide or rings. The gas fouling is loose, fluffy, black, sooty stuff that wipes off easily and doesn't create a hard, baked-on deposit. Oil fouling, if it is bad, will create a heavy, hard deposit that is also black and oily. If it is not so bad, it will be just a heavy, baked-on dry deposit that can be picked off with a small screwdriver. Oil fouling caused by a leaking valve guide (usually intake) tends to create the fouling more on one side of the plug. My guess is you have a bad guide and valve stem seal.

[Mook]

Hey Malky, the deposit was like the third example that you gave, it was heavy but came right off with a little screwdriver. So what should be my next move? About two years ago I did put a RPM intake on and was thinking about putting the stock one back on, could my intake swap caused this problem?....I was thinking that I was going to get more performance out of the Eldelbrock intake, I now know that they are pretty much the some intake!

[Jack Gifford]

I agree with some other posts, that an intake valve stem seal is quite suspect. But you mentioned two things- a manifold change and a rocker cover leak- so there's also a small (very small?) chance that your manifold change left you with a tiny leak around an intake port, which could draw oil that leaked from the rocker chamber.

[Malky]

No, the intake is unlikely to be the problem since your valve cover oil leak was on the plug side.
Next move? It depends on how much you want to fix it.
The cheap option is to just keep running it and change the plug when the idle gets rough. I have done this, but then I'm Scottish.
Next option is to replace the intake valve stem seal on the bad cylinder and hope that fixes it, at least for a while.
Next option is to pull the head(s) and redo the guides, valves, and seals.
And if that doesn't fix it, then you have a broken or damaged oil ring on that cylinder, but that is unlikely.

[ambmech1]

One quick check since you said that it is the plug furthest back and that the valve cover was leaking. Since the engine is tilted a little towards the back, I would pull the valve cover off and make sure the oil returns are not blocked or plugged. That oil has to go somewhere and if your valve seals are not quite up to snuff thats where it will go.