2003 Suburban 2500 Secondary Fuel Pump

[wellis77]

Hey everybody, I've read a number of threads here but haven't been active until today.

 

I have a 2003 Suburban 2500, 6.0l. Early this year I replaced both fuel pumps, the primary pump was going bad (low pressure, couldn't keep the truck running) and I decided to replace both with 180,000 on the odo. Everything has been great until I recently heard an odd humming noise. It appears that my secondary pump is not shutting off when the secondary tank is empty. Getting good information on how this system works seems to be tough but I imagine when the fuel level in that tank drops to empty the relay is supposed to shut that pump off. Sound right? If that is the case I probably have a bad secondary relay and my next two questions are (1) where is that relay and, (2) is that the five pin relay? My searches for fuel pump relays have four pin and five but don't indicate primary or secondary.

 

Any other thoughts of what I might need to look at or look for with this issue?

 

Thanks.

[davester]

I don't know if the setup on your Bur is the same as my Cab&Chassis (also has two tanks), one of the computers controls when the secondary tank's pump runs, based on the level of both tanks.

 

I suppose it's possible that the relay (if there is one for it, IDK for sure) is frozen closed, but I would first check that the fuel level sensor/wiring for it is working properly.  This is because if the computer thinks the rear tank is full, but the front tank isn't, it will pump fuel from the rear tank to the front tank until they are about equal, and if the rear tank is empty but the sensor reads it as full, it will run the pump all the time.

 

And if this is happening (tank is empty, but pump is running), there is a good possibility you have to buy another pump, as the fuel lubricates the pump components as it is being pumped through.  If the pump runs dry, it generally fails after a short period of time.  I recall when I changed the FP's in my truck, one of the pumps included a sheet indicating the warranty for the pump was void if it was run dry for more than 3 seconds...