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function of the crank/rpm sensor???? 900

posted by  Don Foster on  Thu Jan 1 10:39 CST 2004
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last visit: Sun Oct 5 11:53 CST 2014
[RELATED]

"The fuel pump pressurizes the injectors as soon as you turn the key."

I may be spliting hairs here, but that isn't exactly so. The fuel pump sometimes runs for a second when the key is turned on, but that only occurs when the ignition system is powered and the sensor detects a signal at power-on (happens when the sensor and vanes are positioned just so). This produces a single spark pulse, which triggers the fuel pump relay.

That is a random event and doesn't always occur. And it's most likely NOT an intended design feature.

The fuel pump and pressure accumulator have a check valve intended to maintain fuel pressure when the engine is shut off -- and that's so the system has pressure for the next start up.

If you have no crank signal, you have no spark. No spark means the fuel pump relay does not power the pump. No pump means no pressure beyond what's held by the check valve.
--
Don Foster (near Cape Cod, MA)






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