Ok, so I have a friend that has a 1996 (I think) Saturn with the 1.9 liter engine. It keeps fouling the #4 spark plug after about 3,000 miles. All other plugs look fine. Any ideas?

Engine runs good till the fouled plug thing happens and it starts misfiring. Car has a manual transmission. Car has regular scheduled oil changes. Compression across all 4 cylinders is within 10psi of each other.

The owner hasn't thrown any money at the car to figure out the problem......just when it starts misfiring, she has me replace the plugs.

Lots of white crusty build up on the bad plug every time. All other plugs look normal with light a white/brown "dusty" appearance.

I'm thinking an injector issue.....injector flow partially restricted......Combustion chamber running lean, getting hot.....Last time I replaced the plugs, the center electrode had corrosion built up which fully fused the center electrode to the outer electrode. Not metal-to-metal.....but a bridge of corrosion.

Any ideas???

Take a look at these pictures and let us know which one looks like the fouled plug:


http://www.aa1car.com/library/reading_spark_plugs.jpg

Looks like the one labeled ASH DEPOSITS.

(Guess I will replace the valve guide seal (as suggested in the photo).