At 05:49 PM 3/7/02, Ernest Gilman wrote:
>I must be missing something. My fuel pump begins running as soon as I turn the key on. Always has. Has it been defective for the 15 years that I have owned it?


As far as I know, no modern car or truck is set up that way. While the chances of a problem are slim, there are some risks involved with having the pump run anytime that the ignition is on, rather than only when the engine is running.

In a major accident with a fire, the pump could continue to pump fuel into the fire.

In an accident with no fire, the pump can cause a fire by pumping fuel from a damaged line or injector.

If the engine quits but the ignition is left on, a leaking injector could fill a cylinder with fuel, causing a hydrostatic lock and severe engine damage, or could dilute the engine oil with fuel, causing engine damage.

The 928 uses special pump relays triggered by the ignition system on earlier cars, and an ECU-controlled relay on later cars to ensure that the pump runs only when the engine is running, plus a couple of seconds when you hit the starter.

Some cars use an oil-pressure operated fuel pump safety switch.

Wally Plumley

U25 is the 12v power that feeds the pump