Quote:
Originally Posted by LMP
Yes..the prime would run only on the first KEY ON..then the pump will wait for crank signal (fed through the ignition module) to turn on again. Pump relay is acted on by the ECM (as well as injectors) , and ECM waits for crank pulses. Turning key OFF then ON will NOT prime again, except if you wait for several minutes. THis is designed so you cannot flood the engine.
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Each time the ignition is turned to the RUN position, the ECM activates the fuel pump relay for 1 to 2 seconds, (pump prime). The fuel pump pressurizes the system past the injectors and up to the fuel pressure regulator. The regulator bleeds any air that might be in the pressure line back to the tank, along with any excess fuel, and allows the system to acheive operating pressure. The injectors are not activated, (opened) during pump prime.
When the ignition is turned to the START position, the fuel pump relay is activated continuously provided the ECM receives a pulse signal from the crankshaft position sensor. After the engine is running, and the ignition is turned to the RUN position, the ECM will keep the fuel pump relay activated, as long as it receives a signal from the crankshaft position sensor. If the signal is interrupted, the engine will stall, and the ECM will deactivate the fuel pump relay 1 to 2 seconds after the crank signal is lost.
The ECM sends a pulsed ground signal to the injectors based on the signal from the crankshaft position sensor. The ignition module, (which fires the ignition coil), is also controlled by the ECM based on the same data from the crankshaft position sensor.
If the throttle is held wide open during cranking, the ECM will not activate the injectors. The is only means for unloading a flooded engine, there are no provisions to prevent flooding.