Re: Straight answer (archive)

There are fuel injection systems that actually prime the fuel rail when you turn the key to the ignition "on" position. Late model Ford systems and probably late model BMW systems (certainly not ours) do this. On my Ford I hear the fuel pump run for a second and then cut off if I don't start the car. I think the confusion with the "on" and "run" positions is that you need to add the state of the engine to properly define them. When you turn the key to the last position before the "start" position you should use the "on" term since the engine is not running. When you turn the key to the same position from the "start" position then you should use the "run" term since the engine is running.

Now on both my BMW's, an 87' 528e and 85' 745, I notice no fuel pump priming in the "on" position. The fuel pump only runs in "start" and "run". I've confirmed this with a pressure gauge. Even the Bosch fuel injection book indicates that the fuel pump runs in the "start" position. It even states that if the ECU doesn't receive a signal that the engine is running (faster than 150 rpm) it will shut the pump down to prevent flooding. Looking at the fuel delivery control schematic it seems that the ECU grounds pin 20 to activate the fuel pump. Obviously, you can jump the relay to turn the pump on for troubleshooting but normally the ECU controls the fuel pump relay.

Hope I didn't add to the confusion.

demet

Follow Ups:

FINALLY!!...Thanks Demet!! Aaron 21:44 12/05/2000 (2)
- Re: FINALLY!!...Thanks Demet!! demet 22:15 12/05/2000 (1)
  - Why it works as such... Winston 23:41 12/05/2000 (0)

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