These are my AC Delco rapidfires. They are 10 months old. All the plugs look OK except cylinder #4 which has what I guess are ash deposits? They don't seem too bad but I'm wondering why only that cylinder has them. I took them out to inspect them because I'm getting a slight misfire under load.

All 6 plugs:
http://jlg.net/photos/bonneville/all-plugs.jpg

Close-up of #2 and #4:
http://jlg.net/photos/bonneville/plugs2-4.jpg

It'* only the outside of the ground electrode that'* white. The ring at the base of the ground electrode is white also. The center electrode is fine. If the wire going to that plug had a bad connection, could that misfire cause the plug to turn white?

Oil burning in the cylinder can cause that effect as long as the oil leak isn't severe. Severe leaks have a totally different effect on a plug. That'* one possibility for you. Another is that it might have been gapped wrong when purchased/installed.

Oil leaks are probably most likely valve stem seals in your case. You may want to try an oil additive advertised for it'* 'reconditioning of seals' benefits. Or simply pull your new plugs and check them again in 6 months.

This is just my opinion, to me #4 actually looks normal, and the rest look carbonized. But I really cant see then that well.... :?:

SMALLBLOCK - It'* hard to tell from the photo but I compared them to new plugs and #4 is indeed whiter - the other 5 plugs are the correct color. However the threads on the other 5 are dirty.

The old plugs were Rapidfire #3'* and were supposedly pre-gapped at .045". I checked them all and they were all about .048" on my gauge.

Here'* an update:

The wires are less than 6 months old. I re-coated the ends with silicone goop but no change. I changed the plugs and now it no longer misifires under load. The bad news is that although the misfire is gone, it lacks power when the TCC is engaged, but that'* another story.

Regarding the possible oil leak - I got a Valvoline oil change and dumped in some stop leak. It later occurred to me that using Valvoline Max Life instead of normal 10W-30 might be an alternative? They claim it reconditions valve seals.

i used that for a while on my 82 cutlass (before it died, may she rest in piece), and it worked great for me... the car ran quite a bit better and stopped puffing smoke anytime i breathed on the gas pedal.

or you could just replace the valve seals... on the 82, i ended up doing that. isn't too bad either (of course, that was RWD). some compressed air, a compression tester hose, valve spring compressor and a magnet (After you get off the valve cover and spark plug), and a little patience. nothing to it...

connect the compression tester'* hose to the spark plug hole (need to remove the valve dealio in it, but you can pick up the tool to do that for about 1 or 2 dollars), and connect that to some compressed air (normally, you'd want that piston to be all the way at the bottom, but if you've got some balls, and you're careful, you'll pretty much be able to force the piston down with the compressed air). while the air is going into the cylinder, the piston is forced to stay down while the valves are forced to stay up. which works out wonderfully. take a valve spring compressor (15 dollarsish) and compress the valve spring. with it loose, drop it as low as it will go, and with magnet in hand, remove the keepers (or valve locks if you prefer to call them that). pull the spring up, and viola. at least on the 82, you'd be looking at the rubber valve seal. of course, on that particular year, they were only on the intake i believe...

but still.

by the time the car died, i had it to the point where i could do half of the motor in 30 mins from hood open to hood closed. (did it one side at a time, and screwed up the first time because i thought they were all supposed to have them, at the insistance of my mechanic friend <- so I had to do it all over again).

easy to do, and welllll worth the low cost of doing it. i had been going through a quart every 300 miles or so (i know, i know), but it went down to about 5 or 600 miles. i also had a major leak from my rope gasket on the timing chain cover, but never got up the desire to put myself through that repair. and then of course, it died... but that'* another story.

so i just made a really long post out of what was going to be a very short post... basically, stem seals are a pretty easy to do job, and well worth the time spent...

of course, now looking at an auto parts website, i can't seem to find stem seals for our motor... do we have them, or do we just have guides? hope i didn't make a really long entirely pointless post...

Glad you got rid of the misfire. I guess if threads were dirty enough it could cause a resistance to ground (block} and cause a misfire under a load. Maybe just a bum plug. 048 aint bad unless a coil is marginal. I used to expeirment alot with gaps and Ive found; the wider the gap {to a point}, the smoother the idle, but the high end can suffer. Smaller gap, a little rougher idle,but harder pull especially at launch, then the high end will suffer. the coil state determines optimum gap. but who really cares, right?

I have to agree that #4 looks better than the other plugs, in the picture. Where is all that crap coming from on the threads?

There is no way you could insulate the threads so that it would misfire, even if you wanted to. So that doesn't explain anything.

How often do you change your oil? As it ages you tend to burn more, and that will mess up your plugs.