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What keeps me up at night...

Kay86K5 said:
First off, doesn't matter if its 5.3, 6.0, or 8.1, fuel pressure requirements are the same. The difference comes in the injectors and what they are rated to depending on the spec of the motor, but the requirement for fuel pressure at the rail is going to be the same for all of them...just to clear that up.
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No, you have to consider both the pressure and the flow on any fuel system (i.e. gpm). It may be you can use the same pump for those 3 engines, but it's not true in the general case. Typically at some point of adding power you'll need a higher flowing pump, even if the pressure is the same.

You wouldn't say all 12V accessories have the same power requirement....
 
Blue85 said:
No, you have to consider both the pressure and the flow on any fuel system (i.e. gpm). It may be you can use the same pump for those 3 engines, but it's not true in the general case. Typically at some point of adding power you'll need a higher flowing pump, even if the pressure is the same.

You wouldn't say all 12V accessories have the same power requirement....
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I was going to make that comment but I was busy.
 
Only talking about stock motors, and factory specs say the same for pressure at the rail. Yes, when talking about built motors, I would agree
 
Larry's running both tanks in the K10, but only feeds the engine off of one. The other tank is purely storage that has a lower pressure pump to transfer fuel from the secondary to the primary. Since he made that change he's yet to have a problem. That's with a ton of mileage on and off road.

The only issue he's had is forgetting about the transfer pump running and barfing a couple of gallons of fuel on the ground when it overfills the primary tank.
 
If you run the stock 8.1L ECM, it should have provisions to control 2 fuel pumps. While the physical layout may be different, there should still be a way to run dual sending units and pumps and let the ECM transfer fuel from the secondary to the main, just like in the GMT800 dual tank setup. You could also try to retrofit the factory 2000-2006 diverter valve to fill both tanks from one neck - don't know how far apart the tanks can be for this to work.
 
Blue85 said:
If you run the stock 8.1L ECM, it should have provisions to control 2 fuel pumps. While the physical layout may be different, there should still be a way to run dual sending units and pumps and let the ECM transfer fuel from the secondary to the main, just like in the GMT800 dual tank setup. You could also try to retrofit the factory 2000-2006 diverter valve to fill both tanks from one neck - don't know how far apart the tanks can be for this to work.
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I'd love to figure that out but this may be over my head
 
ZooMad75 said:
Larry's running both tanks in the K10, but only feeds the engine off of one. The other tank is purely storage that has a lower pressure pump to transfer fuel from the secondary to the primary. Since he made that change he's yet to have a problem. That's with a ton of mileage on and off road.

The only issue he's had is forgetting about the transfer pump running and barfing a couple of gallons of fuel on the ground when it overfills the primary tank.
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Yea I spoke with Larry about it via pm but I think I'm going to put my transfer pump on a momentary switch so I can't forget to turn it off as I watch the fuel guages
 
Blue85 said:
If you run the stock 8.1L ECM, it should have provisions to control 2 fuel pumps. While the physical layout may be different, there should still be a way to run dual sending units and pumps and let the ECM transfer fuel from the secondary to the main, just like in the GMT800 dual tank setup. You could also try to retrofit the factory 2000-2006 diverter valve to fill both tanks from one neck - don't know how far apart the tanks can be for this to work.
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That system is problematic in stock trucks at times. They still use it on 900's and the K2x trucks too that are cab/chassis with dual tanks. It don't work the way we would want it in a square. That system uses no switch to read fuel level independently from each other. It takes both sender values and creates an average between the two to simulate one sending unit. So when the fuel level gets to a certain point it turns the transfer pump on until the front (primary) fuel level comes up and then it shuts the transfer pump off. The fuel level sender values go to the PCM first and the PCM sends a value via class 2 serial data to the cluster for the fuel level gauge to use. Meaning, the regular resistance to ground value the stock Squarebody fuel gauge operates on is not going to accept a value via class 2 serial data. You would have to go with a dakota digital cluster IF it accepts the Class 2 serial data or use a GMT800 cluster in the square.


Another option. FULL DISCLOSURE: I've not used nor have I done anything more than seeing this in another forum. I can't vouch for if it works or the level of quality this guy puts in his kits. Pics look decent, but check the guy out yourself if you are interested. That being said, I found this on the 67-72chevy truck page under the squarebody section. This guy has assembled his own harness/relay kit and combined with a 65psi switch valve to run two walbro pumps for LS swaps to a square. Here's the link. http://67-72chevytrucks.com/vboard/showthread.php?t=713194
 
ZooMad75 said:
That system is problematic in stock trucks at times. They still use it on 900's and the K2x trucks too that are cab/chassis with dual tanks. It don't work the way we would want it in a square. That system uses no switch to read fuel level independently from each other. It takes both sender values and creates an average between the two to simulate one sending unit. So when the fuel level gets to a certain point it turns the transfer pump on until the front (primary) fuel level comes up and then it shuts the transfer pump off. The fuel level sender values go to the PCM first and the PCM sends a value via class 2 serial data to the cluster for the fuel level gauge to use. Meaning, the regular resistance to ground value the stock Squarebody fuel gauge operates on is not going to accept a value via class 2 serial data. You would have to go with a dakota digital cluster IF it accepts the Class 2 serial data or use a GMT800 cluster in the square.


Another option. FULL DISCLOSURE: I've not used nor have I done anything more than seeing this in another forum. I can't vouch for if it works or the level of quality this guy puts in his kits. Pics look decent, but check the guy out yourself if you are interested. That being said, I found this on the 67-72chevy truck page under the squarebody section. This guy has assembled his own harness/relay kit and combined with a 65psi switch valve to run two walbro pumps for LS swaps to a square. Here's the link. http://67-72chevytrucks.com/vboard/showthread.php?t=713194
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This is similar to the harness I was going to build but I'm going to read further into it. Seems he's still using a stock selection valve and that lies the problem for the return causing too much pressure at the rail
 
Yes, like you say the transfer function should work in theory, which is what I was talking about. For the fuel gauge you could run a scangauge or use a custom interface circuit from the sending unit in the main tank. Somebody might make that interface. I agree it's complicated enough to make other solutions look better. If you were grafting more of the donor vehicle systems in it would start to shine.
 
SpeedlabDan said:
Yea I spoke with Larry about it via pm but I think I'm going to put my transfer pump on a momentary switch so I can't forget to turn it off as I watch the fuel guages
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I used a drag race toggle switch that has a bright red light on it when you have it in the on position to run the transfer pump. That way, hopefully I'll notice the bright red light in my face reminding me that the transfer pump is on and to pay attention to turn it off. About as idiot proof as I could come up with (granted, an idiot came up with it :whistle:)
 
Kay86K5 said:
I used a drag race toggle switch that has a bright red light on it when you have it in the on position to run the transfer pump. That way, hopefully I'll notice the bright red light in my face reminding me that the transfer pump is on and to pay attention to turn it off. About as idiot proof as I could come up with (granted, an idiot came up with it :whistle:)
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IMG_20170128_135707.jpg
 
Turns out I do have an open toggle in my panel... Too bad it's in my K5 but I had originally ordered my panel with a fuel toggle before I decided to run Fitech. It does light up lol
 
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