i just changed the plug in my 5.2 and the #7 plug (as i have determined from diagrams on google) was incredibly fouled. it had carbon built up on it so bad i couldn't see the electrode. does anyone know any possible causes for this?

 

lots of possible causes... bad plenum gasket or bad rings or possibly damaged piston/wall come to mind...time for a compression test...I suppose if you have intermittent spark it could get fouled like that too...

 

Are you sure it was 7 not #8? Just asking because #8 is the most common to do that. 7 is driver side rear, 8 is pass side rear. Usually due to clogged cat, bad plenum, etc.

 

it was #7 then it came out of the driver side rear. #8 was fine

 

Check the cap/rotor, ohm the wires. Check for any arcing. Also what Auggie said.

 

Crudded up like that it's a loss of oil control on that cylinder. I'd do compression and leak-down tests and check the plenum gasket. If those all check out, it's likely a worn intake valve guide and/or stem seal -- you can spot either with a vacuum gauge, usually.

 

how do i perform a compression test?

 

Get a gauge..... Take out all the spark plugs. disconnect the electrical connector for the coil. Unplug the fuel pump relay. Put a brick on the gas pedal, to hold the throttle all the way open. Screw the tester into number one spark plug hole, crank engine 5 or six times. Record reading. Take gauge out, put in a teaspoonful of motor oil, but the tester back in, crank engine five or six times. Record reading. Repeat for all cylinders.