Problem: Sparkplugs fouled at base, less than 100 miles after putting them in. XJ6 SIII 4.2L Sedan

There is a thick shiney black deposit right on the metal base below the threads but not so much deposit on the insulator or tip.

It starts up ok, then after 4-5 min driving rpm starts to slow.
Car runs at much lower rpm, no power but has an even rpm and sounds like putt putt putt.

What can I do to correct this condition?

Prior work;

Fuel Changeover solenoid was bad and replaced.
Finally got that working.

Replaced sparkplugs. Ones I took out were nice looking light grey.
Now this sparkplug problem.

Changed fuel filter and air filter.
Put Seafoam into fuel tank.
Still this sparkplug problem.

Needs frequent sparkplug changes.

Thanks in advance,
BrightonRay

 

Not sure if I understand. Are you talking about deposits where the hex head and the threaded portion come together, where the washer seats? If so, I'm not sure that's much of a problem....unless the build-up so bad that in interferes with the plug seating on the head and thus causing a poor ground.

Is this an oily deposit? Are your cam covers leaking?

Do the frequent plug changes eliminate the running problem you described?

Cheers
DD

 

HI,

The way I was describing it was the area inside the cylinder.

Not the hex area or seal. (threads are clean, no oil there)

Rather, inside the cylinder by the Insulator tip where the side electrode is welded to the metal. Insulator is still white. Its on the metal.

Right there where the side electrode is welded to the metal base, that is where the deposit is building up. All around that metal area.

RE:There is a thick shiney black deposit right on the metal base below the threads but not so much deposit on the insulator or tip.

Per Wiki: Insulator tip
On modern (post 1930's) spark plugs, the tip of the insulator protruding into the combustion chamber is the same sintered aluminium oxide (alumina) ceramic as the upper portion, merely unglazed. It is designed to withstand 650 °C (1,200 °F) and 60,000 volts

Side (ground, earth) electrode
The side electrode is made from high nickel steel and is welded or hot forged to the side of the metal shell. The side electrode also runs very hot, especially on projected nose plugs. Some designs have provided a copper core to this electrode, so as to increase heat conduction. Multiple side electrodes may also be used, so that they don't overlap the central electrode

Hope that helps to locate the region.

Thanks in advance,
BrightonRay

 

I suspect your older spark plugs were of a hotter heat range than the present ones. But, if the replacemets are numbered the same and of the same brand, that thought is less likely to apply.

And, you may have changed fuel sources for a brand that burns a tad differntly. refineries have summer blends and winter blends in at least some areas.

And, oils differ in some ways. Have you changed brands and/or viascosities.

And, over rich fueling may have found unburned fuel migrating to the sump and thinning the oil so more gets past the rings into the combuation chamber. Seen by you o the spark plugs?

Just rapid muses without deep thinking. I'll let you tand perhaps others think those out.

Carl

 

Thanks for suggesstions thus far.

Got to thinking about spark plug reading...

The carbon build up around base was not sooty.
And the finish although shiney was not oily to the touch.

Got to thinking that some cylinders were not firing at all.
Did basic test to pull plug boots with insulated pliers
and test spark against valve cover nuts.
#4 no spark
#5 no spark
#6 very weak spark
Was running on 3 cylinders.

Had old distributer cap and rotor in trunk.
Changed back to it and retensioned wire connectors there.

Will get new distributor cap/rotor and new
Kingsborne plug wires this week.


Put in E3 plugs, 4 5 6 now firing ok.

Thanks in advance,
BrightonRay