Dual Fuel Tanks and TBI swappin'

[JCampbell]

As some of you may know, I'm converting my dually over to TBI.

Is there any reason I can't reinstall my original '77 dual fuel tank setup & switch and simply run an external electric fuel pump mounted to the frame rail to feed the engine?

Sure seems like a whole lot less effort and expense than swapping 87+ tanks, twin pumps/sending units and trying to figure out how to wire it all up.

[KazuyaIB]

For my tbi swap i kept the original 86 tanks on my truck, just keep the fuel level above a 1/4 and your ok. The wiring is simple but does require routing it and changing the sending units and switch... just find a donor truck at a local pick n pull. I haven't done the external pump soo I don't know how effective it will be or if it is problematic, but there is plenty of info on wiring and getting it setup. I personal love it the original factory way. Each fuel tank with its own pump. One goes out and with the flip of a switch problem fixed!

[bluex]

Ya I have always heard that the electric pumps are better at pushing than pulling which is why you want them in or as close to the tank as possible. They are also quieter in the tank.

It might work though. My only concern with it would be it sucking air when switching tanks....
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[JCampbell]

Why would an electric pump suck any more/less air when switching than a mechanical pump?

[bluex]

I doubt it would but the problem I see is with pressure.

Mechanical pumps were used for carbs and with the fuel bowls on them I don't think that slight moment of air/no fuel pressure would bother them.

Tbi or any fi on the other hand has no reserve like a fuel bowl and that moment of no pressure would more than likely cause the engine to stumble if you swapped tanks with the engine running. It would probably be fine if you only swapped tanks at idle or with the engine off. I wouldn't do it driving down the road personally.

I'm no expert and could possibly be wrong, but this is one thing that would concern me with one pump. GM didn't put one in each tank to be nice. If they could have used one pump for both tanks then they would have just to save the money per unit. I know it doesn't sound like much but saving even .10 per unit is huge!
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[BigBlocksRule]

TBI still has a return line that will bleed off any air bubbles, etc. when you switch tanks.

[rs72z]

Originally Posted by BigBlocksRule

TBI still has a return line that will bleed off any air bubbles, etc. when you switch tanks.

I had a aftermarket tbi system once that used a electric pump on the frame, it sucked. Anytime it got hot outside it would vaporlock.
I have done a couple of factory tbi swaps, i swapped tanks. Your stock change over valve should work with the tbi setup, i think they only run 16-18 psi.
Swap tanks you will be happier in long run and you dont have to worry about it stalling when you get to a quarter of a tank.
You might consider swapping in a burb rear tank, then you only have one pump.

[hatzie]

Yes you could use the 87+ tanks and pumps with the 73-83 solenoid valve.
Power the fuel pumps with a 30Amp SPDT ISO relay switched from the same wire as the tank valve.
I'd use a MetriPak 630 skirted and sealed relay with its mating connector you can place it on the frame close to the tank valve to make all but one of the wiring runs short and clean. Just grab relay switching power with a short wire and ring terminal on the tank valve. The additional wiring from the cab for the pumps will be a single SXL jacketed wire from the fuse block for Ignition Power (off in accessory position because the pumps will run when it's powered). Wire-tie your new harness to the existing tank harness.

Hook 12v ignition power to Pin 30, Chassis ground to Pin 85, Tank Switch power to Pin 86. The AUX tank pump + will need to be on pin 87 and the main tank pump + on 87a.
Coat the socket and pins with di-electric grease to keep the corrosion at bay.

[JCampbell]

I posed my question to Howell Engine and received the following response:

“We have done systems for vehicles with dual tanks and have not had any issues that were reported to us with the external fuel pump.

Matt Howell”

A simple response, but one would think that with all the conversions they have done over the years that they would have at least heard something if the external pump was problematic w/ dual tanks.

[wyattglock]

After all the trouble I have had with gas tanks and fuel pumps, I have considered doing the same thing. Using the carb sending units and a frame mounted pump should work from everything I have researched.
Not to hijack your thread, but is there any reason why one pump mounted after the switching valve wouldn't work? I would just wire the switch for the tanks to show the individual fuel levels instead of shutting one pump down and starting the other.
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[JCampbell]

Yes, that’s what I was planning on doing. Two tanks, two sending units, one external pump.



Though I’m still considering swapping over to 87+ baffled tanks. Either that, or I’ll construct my own baffle.

[D.FENS]

Wouldn't something like a Walbro 255 be enough?

Ideally, for EFI the pump should be in or at the tank but you can't always re-invent the wheel. The gravity feed out of the tank should create enough pressure to keep the pump from killing itself.

[hatzie]

Originally Posted by wyattglock

After all the trouble I have had with gas tanks and fuel pumps, I have considered doing the same thing. Using the carb sending units and a frame mounted pump should work from everything I have researched.
Not to hijack your thread, but is there any reason why one pump mounted after the switching valve wouldn't work? I would just wire the switch for the tanks to show the individual fuel levels instead of shutting one pump down and starting the other.
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Just mount it below or near the same level as the bottom of the tank.

[JCampbell]

Yeah, that shouldn't be an issue. I'll just mount it down low on the inside of the frame next to the passenger side tank.

[JCampbell]

I'm getting ready to order my fuel pump. I was planning on running the Carter P5001, but after looking at the specs of the P5001 vs. the P5000, I’m unsure about what pump to use.

The P5001 runs 9-22 psi @ 50 gph whereas the P5000 runs 22-75 psi @ 50 gph.

Is there any advantage to running the “larger” pump? It's never going to be a high-horse, monster engine. Just an otherwise stock 454 with a small RV/towing cam and intake?

...and I did order and install baffled tanks.

[wyattglock]

The only advantage to a higher pressure fuel pump is if you upgraded your engine or fuel injection system later. For a stock system the 9-22psi pump with a good bypass regulator will work fine.
Either way, the baffled tanks will help keep the gas under the pickup.
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[JCampbell]

Roger that. Thanks.

[chebyshortbox65]

I'm running duel tanks on a 5.3 swap pump is mounted in front of switching valve you have to check fuel pressure at throttle body the return port on the valve is to small I get 95 psi at the fuel rail instead if 60 it so I belive its because the return fittings are to small at 1/4 I'm thinking of going to a suburban fuel tank or droping in a fi tank on one side and keeping the other tank stock and running a. Transfer pump to fill the primary tank when needed
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