Dude comes into the service station and says... (Tell me if you've heard this one)

[Max Taxable]

He says, "Hey I need a new set of spark plug wires, I read somewhere that increases power and mileage."

Mechanic takes the car for a little drive, and when they return to the station he opens the hood and listens to the engine running. Finally he shuts the car off and says, "Well I can put in new spark plug wires, but your real problem is you have a blown head gasket and a leak in your intake manifold that is causing your mixture to be way too lean, which will eventually burn a hole in one or more of your pistons. You really need a new head gasket and a new intake manifold gasket, this engine is a sick puppy."

The dude thinks about it for a second and says, "Yeah but I read that the spark plug wires can increase fuel mileage 1 percent, and increase power 2 percent."

Mechanic says, "Be that as it may it's not the problem with your car, the spark plug wires you have are doing their job just fine. I wouldn't worry about little stuff like minor performance increases when the engine is running at about half the power it should and easily a third the fuel economy it should."

The dude says, "well you just don't want to address the issue" and takes his car to another service station. Meanwhile, the poor mechanic mentally writes off the hour and a half he just wasted on this guy.

So, the dude buys a new head gasket and intake manifold gasket, and installs them himself. Car runs great now. He goes to another station and asks about new spark plug wires and how they increase performance and mileage, and says please don't talk about anything else. This mechanic says, "Well there's really nothing to talk about then, your car runs great, almost like new. I wouldn't change a thing."