The fuel pump runs on 12 volts, (full battery voltage), through the Automatic Shutdown (ASD) relay. The relay turns on only two times; first, it turns on for about two seconds when you turn on the ignition switch, then it turns back off. It turns on again when the engine computer sees engine rotation, either cranking or running.
The ASD relay sends current to the fuel pump or pump relay, fuel injectors, ignition coil(s), and alternator field. This is Chrysler's answer to Ford's trouble-prone inertia switches. In the event of a crash that ruptures the fuel line, the engine can't run without fuel pressure. When the engine stalls, no more pulses arrive from the crankshaft position sensor so the engine computer knows to turn off the ASD relay. Voltage to the fuel pump is turned off to prevent pumping raw fuel onto the ground. This system has been used for over 25 years and is very reliable and effective.
Why do you think the fuel pumps are burning up? What are the symptoms? Failure of the crankshaft position sensor is more common than the fuel pump. The clue is there will be no spark AND no fuel pressure. That's why it's important to check for both and not just troubleshoot the first thing you find missing.
If the replacement pumps are locking up, suspect microscopic debris in the tank. Many shops are having the tanks steam cleaned when they install a new pump to prevent repeat failure.
If you experience engine stalling when you remove your foot from the accelerator at highway speeds, suspect a plugged pickup screen attached to the pump housing. The engine might run fine for many miles before this symptom shows up. If you are buying replacement pumps from the dealer or, I believe from NAPA, you will get the entire drop-in assembly with the new pickup screen so this won't be a problem. If you buy the pump from other sources, you might only get the pump and motor and have to reuse the screen in which case you haven't solved the problem.
Wednesday, November 11th, 2009 AT 12:33 AM