1999 w210 Fuel pump intermittant

Occasionally, and more frequently as of late, the engine fails to re-start after sitting for a few minutes. I suspected the fuel pump circuit and validated this by attaching a switched buzzer to the relay
that powers the fuel pump(under the rear seat). Using the buzzer, I can verify that the car is not started because power is not being supplied to the fuel pump relay.     In normal function, the fuel pump runs when the key is turned on. Then, I think, once pressure is built up after a few seconds, the fuel pump shuts off. So there must be a pressure sensitive switch to cut power once a specific pressure is achieved. If the key is then turned to start, power is supplied to the relay and the fuel pump will run. Then obviously while the engine is running the fuel pump is always running.     What reasons would the fuel pump relay not receive power while the engine is cranking?
Thanks for your help JB 99 E55 88 300E
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Fuel pump relays become intermittent and need to be replaced. YES the fuel pump is ON for a second or two BEFORE the motor is cranked, after the motor is running it is of course ON. The relay cuts the fuel supply to a stalled motor so that a fuel fire doesn't occur if the car is wrecked and the key left ON. In your car's case the relay has power but the fuel pump doesn't - because the relay is shot.
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-->> T.G. Lambach <<-- wrote:

Thanks T.G. but I may not have made the point clear. The relay is not getting power and thus it doesn't activate. I have the buzzer wired in to the terminals that supply the relay with power. When the car is cranking and not starting, power is not being sensed at the relay. I wait a couple minutes, then start cranking and the buzzer activates, and the relay activates, power is then connected thru to the fuel pump and the car will start. The car starts every morning religiously, without exception. The only time it doesn't start is after I drive for say 20 minutes, shut the car off, come back in 10 minutes and try to start it. Then I crank it for a couple seconds, wait 30 seconds, crank again, wait 30 seconds, crank again, and then eventually it starts. It has never left me stranded. Am I making any sense? Thanks for your help.
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OK, so, once running, the motor never quits. It's only the hot start that's intermittent. Roland suggests a ten second delay interval relay is involved. I don't know. If that's so then I suggest that relay has a heat related failure and that the fuel pump relay itself is innocent.
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I think JB has a hot start problem... which indicates vapor lock... thus leaking fuel injector.
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Tiger wrote:

Tiger would that condition cause power to be absent at the fuel pump relay?
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