Empty the tank with fuel pump

[TJ Baker]

Locate fuel pump relay in fuseblock. Remove relay and place a jumper between terminals 30 & 87. Do not stick anything down in the relay socket that is thicker than the relay pins or you may damage the fuseblock.

 

[Fless]

My 02 has nothing there and I haven’t heard of that. Why would there be a screen there?

Not sure why, but just going off of memory, and I should have taken pics. That's something I forget to do as the work proceeds. I didn't expect to see it but I'm pretty sure there was one. Could be an '03-'06 thing, or a Flex Fuel thing.

 

[Floep]

IIRC my '04 had a (removable, I think,) screen right where the fill tube connected to the tank, so if yours has that a siphon hose won't get farther in. But you can still get quite a bit of gas out using the siphon method.

One of my previous UKON-TAHOE had the same obstruction in the filler, after some sleuthing I found out it was there to prevent fuel theft, so much for siphoning, my 2014 does not have that obstruction.

 

[RET423]

Locate fuel pump relay in fuseblock. Remove relay and place a jumper between terminals 30 & 87. Do not stick anything down in the relay socket that is thicker than the relay pins or you may damage the fuseblock.

View attachment 274291

That's how I do it, I use a paperclip

 

[iamdub]

It’s not a high volume pump, it’s gonna take a long time. Also keep in mind that fuel is actually used to cool the pump and it’s possible you will damage it by running it until it’s empty. It’s always been advised to not run your tank empty because it will destroy your fuel pump, plus you’ll be sucking all the crap at the bottom of your tank through. Think this through. Do you really want to take all day running your fuel pump and probably ruin it, or stick a length of old garden hose in it and siphon it out in minutes.

Not taking sides, but there are some facts to consider:

The pump is designed to stay submerged inside its own bucket regardless of the fuel level in the tank. I don't know what it's called, but through that whole mess on the assembly, suction created by the pump sucks the fuel from the tank through the bottom of an outside bucket then it's dumped into the inside bucket that the pump is inside of. This inside bucket stays filled and the pump pulls from that to feed the engine. Also, they pull from the bottom, so it's already "sucking all the crap at the bottom", anyway. these pump run for hours and hours on end while people sit idling, creeping in traffic, on road trips, etc. They're rated at something like 150 or 190 LPH (I don't recall exactly), which is 40-50 gallon per hour. Based on these numbers, if you were pumping down a full tank, you'd have it done in about half an hour. But, I'm sure that doesn't account for the restriction of the fuel lines, etc. So, lets just double it. I'm sure the pump has an hour's run time left in it.

You could set it up and find something else to do, just keep an eye on it to shut it down as soon as it starts sputtering. It'd be nothing different than if you were running the engine for an hour or however long it takes. Might wanna keep a battery charger on the battery, though.

 

[Rocket Man]

Not taking sides, but there are some facts to consider:

The pump is designed to stay submerged inside its own bucket regardless of the fuel level in the tank. I don't know what it's called, but through that whole mess on the assembly, suction created by the pump sucks the fuel from the tank through the bottom of an outside bucket then it's dumped into the inside bucket that the pump is inside of. This inside bucket stays filled and the pump pulls from that to feed the engine. Also, they pull from the bottom, so it's already "sucking all the crap at the bottom", anyway. these pump run for hours and hours on end while people sit idling, creeping in traffic, on road trips, etc. They're rated at something like 150 or 190 LPH (I don't recall exactly), which is 40-50 gallon per hour. Based on these numbers, if you were pumping down a full tank, you'd have it done in about half an hour. But, I'm sure that doesn't account for the restriction of the fuel lines, etc. So, lets just double it. I'm sure the pump has an hour's run time left in it.

You could set it up and find something else to do, just keep an eye on it to shut it down as soon as it starts sputtering. It'd be nothing different than if you were running the engine for an hour or however long it takes. Might wanna keep a battery charger on the battery, though.

Huh. I figured if it takes all day to burn through a tank of gas with the engine running it would take all day to pump it out too but then I’ve never tried it. It was super easy for me to siphon it in minutes. And I’ve heard it’s bad to run your tank empty but maybe that’s not true? I don’t let mine get below about 1/4 but mainly because I’m supercharged although on my Silverado I did run it empty once and it worked fine afterwards. I found out when that truck says empty it’s empty. That’s a fuel cell though and I had to cut the pump down to fit the height of the cell so the level sender is off. That truck also never sees under 1/4 tank.

 

[ks03]

...plus you’ll be sucking all the crap at the bottom of your tank through.

Every motorcycle rider that has ever had a reserve position on their petcock keeps this rattling around somewhere in the back of their head

 

[Fless]

Every motorcycle rider that has ever had a reserve position on their petcock keeps this rattling around somewhere in the back of their head

It's like what should be done with a water heater at home, exercise that "other" drain periodically and flush the sediment out.

 

[Rocket Man]

Every motorcycle rider that has ever had a reserve position on their petcock keeps this rattling around somewhere in the back of their head

Been there lol.

 

[iamdub]

Huh. I figured if it takes all day to burn through a tank of gas with the engine running it would take all day to pump it out too but then I’ve never tried it. It was super easy for me to siphon it in minutes. And I’ve heard it’s bad to run your tank empty but maybe that’s not true? I don’t let mine get below about 1/4 but mainly because I’m supercharged although on my Silverado I did run it empty once and it worked fine afterwards. I found out when that truck says empty it’s empty. That’s a fuel cell though and I had to cut the pump down to fit the height of the cell so the level sender is off. That truck also never sees under 1/4 tank.

The engine is using only a very small amount of the volume that the pump is pushing. This is where you get pressure from- X amount of volume in a 5/16" pipe trying to squeeze through the tiny orifices in an injector. It can't all fit so it builds up in the system (pressure). That's why there are return style fuel rails. The excess fuel, governed by the regulator, is simply diverted back to the tank. The returnless manifolds have the excess fuel regulated and returned within the assembly.

The fuel pump in our trucks (and pretty much any vehicle since the 90s) has no idea of the fuel level outside of its bucket.

Now, if your bucket is like mine and isn't holding fuel, then you'll run out of fuel on hard accelerations. The fuel sloshes to the back and the pump quickly sucks up what's left, the engine sputters, the truck bucks forward, the fuel rushes back, the pump builds pressure again, the engine comes back to life and launches, the fuel sloshes to the back, etc. It's not a fun ride. In a boosted ride, that's split second that you're lean can end it all on the spot. So, keeping it 1/4 or more is a safe habit.

I don't know how long mine's been leaking cuz I've always filled it around 1/4. When I had the tank drained to clean the carbon pellets, I put in about three gallons I had on hand to get me to the store to fill up. I barely got on the throttle and it sputtered. It was fine after filling up. I have a new pump assembly on hand for when I feel like dropping the tank again.