why does my fuel pump go from loud to quiet after start up?

blackie · 09-22-2004, 01:21 PM

ive always noticed that when you first start the car the fuel pump has a louder tone to it, as if its getting more voltage. but then always like 30-40 seconds later it gets quieter until you turn the car off again. whats going on when i hear this noise? i know its probably normal but im just really curious why its set up like this.

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mbiker97 · 09-22-2004, 01:30 PM

The fuel pump controller has 3 speed settings. When you first turn the car on it needs to pressurize the entire system so it is 100% duty cycle. When you are just cruising it is at 33% duty cycle.

blackie · 09-22-2004, 08:26 PM

Quote:

Originally Posted by mbiker97

The fuel pump controller has 3 speed settings. When you first turn the car on it needs to pressurize the entire system so it is 100% duty cycle. When you are just cruising it is at 33% duty cycle.

does it go back up to 100% at WOT?

ride5000 · 09-22-2004, 10:11 PM

the dc is controlled wrt rpm.

SINthetic · 09-22-2004, 10:13 PM

its pressurizing the system

09-22-2004, 01:21 PM	#1
blackie Scooby Specialist Member#: 42979 Join Date: Sep 2003 Location: houston tx Vehicle: 03 wrx blizzzack stage IV	why does my fuel pump go from loud to quiet after start up? ive always noticed that when you first start the car the fuel pump has a louder tone to it, as if its getting more voltage. but then always like 30-40 seconds later it gets quieter until you turn the car off again. whats going on when i hear this noise? i know its probably normal but im just really curious why its set up like this. * Registered users of the site do not see these ads.

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09-22-2004, 01:30 PM	#2
mbiker97 Scooby Guru Member#: 7922 Join Date: Jun 2001 Chapter/Region: MWSOC Location: Tucson Vehicle: 04 CTS-V b/b/b 99 GMC Highrider	The fuel pump controller has 3 speed settings. When you first turn the car on it needs to pressurize the entire system so it is 100% duty cycle. When you are just cruising it is at 33% duty cycle.

09-22-2004, 10:11 PM	#4
ride5000 Scooby Guru Member#: 32792 Join Date: Feb 2003 Chapter/Region: NESIC Location: lincoln, ri Vehicle: 2003 GGA MBP 12.9 / 105+	the dc is controlled wrt rpm.

09-22-2004, 10:13 PM	#5
SINthetic Scooby Specialist Member#: 53775 Join Date: Jan 2004 Vehicle: 03 WRX Silver	its pressurizing the system