Absolutely. Here's a copy / paste version of an earlier reply. After reading this, holler back with more questions:
When you turn on the ignition switch, the engine computer turns on the Automatic Shutdown (ASD) relay for one second, then it turns back off until pulses arrive from the crankshaft or camshaft position sensor. These pulses only occur when the engine is rotating, (cranking or running). It looks to novices like the computer isn't turning on the ASD relay if you're troubleshooting the system while just leaving the ignition switch turned on, but that's what's supposed to happen. That one second that the relay turns on is enough to run the fuel pump to insure fuel pressure is up and ready to start.
When crankshaft sensor pulses arrive during cranking, the engine computer turns on the ASD relay constantly. Voltage from the relay feeds 12 volts to the ignition coil(s), fuel injector(s), alternator field winding, oxygen sensor heater, and the fuel pump or fuel pump relay. Ever hear of Ford's silly inertia switch? It will kill the engine if you hit a big enough pothole. Chrysler accomplishes the same thing much more effectively with the ASD relay.
If you are in a crash that ruptures the fuel line with roughly 50 psi, the in-tank electric pump will pour raw fuel on the ground creating a severe fire hazard. With a ruptured line, you won't have fuel pressure. Without pressure, the injectors won't spray fuel and the engine will die. When there is no rotation, there's no crankshaft sensor pulses so the engine computer turns off the ASD relay and removes the voltage supply to the fuel pump.
To troubleshoot this system, you have to bypass the ASD relay with a paper clip or you have to work on it while cranking the engine, (not very practical).
Ok, now to add to the story, the air gap for the crankshaft position sensor is critical. New sensors come with a thick paper spacer stuck to the end to set that gap. It slides off as soon as the engine is started and is done doing it's thing. If you remove and reinstall that sensor without the spacer, such as when replacing the transmission, it will likely hit the flex plate and be broken. That will result in a no-start condition.
Many aftermarket replacement sensors have a thin plastic rib molded on the end of the sensor to set the gap. It will partially wear away when in operation. To remove and reinstall those, you are supposed to cut the remaining rib off and use a paper spacer. You can get the paper spacers at the dealer's parts department.
Sunday, December 5th, 2010 AT 6:09 PM