Dear Car Talk:

I have a 2003 Chevy S-10 V-6. I go out on my lunch break, and the truck starts, no problem. I get some food and go to restart the truck, and I can't get it to start. I call my boss, and he heads over to give me a jump. In the meantime, a couple of old-timers wander by, and they want to solve the puzzle. I pop the hood, and they start diagnosing. We determine that it has gas, the battery is not corroded and the battery connections are fine. My boss shows up. Further diagnosis ensues. I have spark, they decide. They trade out some fuses and determine that the fuel pump fuse is good. So now there are four of us crawling all over my car: me, my boss, old-timer No. 1 and old-timer No. 2. Then a random mechanic walks by, and we ask him. He tells us to hit the gas tank with a hammer. "Very funny," we say. 

"No," he says, "I'm serious." He says to hit the tank with a hammer while someone tries to start the car. There's no hammer around, but there is a rock, and my boss hits fuel tank with the rock while I turn the key, and the engine starts! Have you heard of this before? Do I need to replace my fuel pump?

-- Mike

Yes and yes. I have heard of it, and you need a fuel pump.

When electric motors die, they can sometimes be coaxed back to life temporarily with a whack upside the head (and yes, that's the technical term).

In fact, we often whack them as a quick test. If we suspect that an electric motor has failed -- whether it's a fuel pump or a power-window motor -- the first thing we'll try is banging the motor, or the thing that houses the motor, while operating the switch. If we can get it to work that way, that tells us there's a 99 percent chance that the motor needs to be replaced. 

The reason this works is that, eventually, when an electric motor gets old, the armature stops rotating. And banging the motor will often jar the armature just loose enough to get it going again -- for a while.

But sooner or later (probably sooner), your fuel pump will fail again, because it's in the process of dying. And you may be lucky enough to get it started with the help of a rock and a random old-timer. But eventually, banging it won't work anymore. Or you'll use too sharp a rock and pierce the gas tank and set the truck on fire.

Then, at least, you won't need a fuel pump, Mike. Good luck.