Aftermarket EFI and dual internal pump tanks

[bluex]

Great info Blue thank you, I opted for the PF4 XT recently that was not available at the time of my build that’s why my Sniper is in the classifieds, that said I do now need to run an external regulator and yes my truck is an 86 but did come with factory dual tanks… Perhaps AA has an 87 tank harness ? My head scratching is that wouldn’t the fuel pressure need to be regulated after the pumps but before the Pollak so the issue you had dosen’t occur ? The sniper is regulating fuel at the throttle body therefore the Pollak would be getting hit with full pump pressure is that not correct ?

System pressure is the same regardless of where it's regulated. Pressure is a measure of system restriction, yes the pump is capable of producing 100-110 psi if needed but if you just put a hose on it an let it pump into a bucket there's no pressure.

So wherever you regulate the pressure it'll be the same at the valve assembly. In general the return side is usually always less than 5 psi because that is after the regulator and the only restrictions are the hose itself and any bends or fittings.

 

[Fastduramax]

Haha ! Good to know my thinking slash theory on fuel pressure was completely wrong ! I just read a thread Barnes wrote having the exact same problem you have had and it was all solved by a wiring change, I will have to look at it on my PC and not my phone but will still likely be a foreign language to me

 

[SquareRoot]

Mike, did you use the EFI tank kit with the separate fuel pump and sending unit ? I see the Pollak has a max of 65psi how did you regulate the pressure before the Pollak ? How do you wire it to have one pump shut off when you switch to the other tank ? Sorry for my lack of knowledge of the inner workings of dual tanks

If you're regulator is set at 43 or 58 psi, that's the max pressure any part of the system will see. It will only go above that if you have a restriction somewhere ( kinked hose, bent tube, etc ). You will need a second switch and a relay circuit that only controls the pumps. The valve and fuel gauge will remain stock with the OEM circuit. I'll post my diagram here shortly.

 

[Hunter79764]

I've got no input on the tank selector valve, but x2 on the info about regulators controlling the system pressure, not just what comes after, as long as we are talking about bypass regulators with a return line (which is about all you will find for this application).
Technically speaking, the regulator sets the pressure at that exact location. Upstream of the regulator, the pressure will be slightly higher to overcome the restriction in the line, and downstream it will be slightly lower due to the same thing. If you need to get the most out of the system, try to have your regulator as close to the engine as reasonably possible, but unless you are on the ragged edge or running particularly restrictive fuel line, 1-2 psi won't matter too much, it's well within the adaptive tables on the ECM.

 

[Fastduramax]

Ok Mike I thought you somehow integrated the tank switch and pumps all into one, meaning when you hit the switch to change tanks it also powered up that pump and de-engerized the other….

 

[SquareRoot]

Ok Mike I thought you somehow integrated the tank switch and pumps all into one, meaning when you hit the switch to change tanks it also powered up that pump and de-engerized the other….

That would be difficult because the OEM harness doesn't have any provision for dedicated 12v wires for electric pumps.

 

[Rumbledawg]

Electric fuel pumps are much more efficient at pushing fuel rather than pulling it. I've also seen people put 1 external pump after the valve an run it that way. They always live a short life in that arrangement. External pumps are loud, they don't get the benefit of fuel around them for cooling and are best gravity fed so they are not pulling the fuel. There's no real way to gravity feed them with the stock tanks and valve.

haft to disagree.
i run a pro-flo system for 20 yrs with an external pump in front of the selector valve wit ZERO probs.
although approx 2 yrs ago i did kill my pump by getting too far in the bush and running my tanks almost dry. not the pumps fault, my stupidity going further than my tanks could carry me. i replaced the pump with an exact match (walbro) and expect to get just as good service as my first one. try to never let the tanks get below a 1/4 and you'll be fine..
much simpler and cheaper than dicking with pumps in 2 tanks
can't comment on noise, cause after mine primes, you don't hear a single thing from it

 

[SquareRoot]

Sorry for the delay. I had to search my phone to find this schematic. This is how I run my dual tanks, EFI with 6 port valve and OEM fuel gauge. Actually, Dakota Digital but it works either way. This is a separate, additional circuit from the factory two tank harness. Easy-peasy.

 

[Ricko1966]

Call any fuel pump manufacturer ask them if their pumps push better than they pull. They will tell you they push better than they pull. Read manufacturer installation instructions,for external pumps they will say as close to the tank as possible and as low as possible.Manufacturers went to intank pumps or intank lift pumps if they have external pumps for a reason.

 

[andybflo]

I've put nearly 10,000 miles on a dual-tank LS swap. Dual 1987 tanks (truck is a 1986), two in tank pumps, 1987 ******* valve and dash switch, and a three-relay setup that's been documented here for power. I can even switch, towing, uphill under load. Truck won't even stumble.

I've even duplicated the setup on my GMC Motorhome it worked so well (Sniper EFI on that one, pushing with a fuel mat and horizontal pump due to the shallow tanks.)

Legitimately, it's been trouble free other than when yours truly tied the wrong sending units into the wrong tanks. Easy enough fix, but I was getting like 50mpg per the gauge for a while.

They all run 40-60 psi, and work fine with the TBI spec'd ******* valves. Never an issue.

 

[Rumbledawg]

Call any fuel pump manufacturer ask them if their pumps push better than they pull. They will tell you they push better than they pull. Read manufacturer installation instructions,for external pumps they will say as close to the tank as possible and as low as possible.Manufacturers went to intank pumps or intank lift pumps if they have external pumps for a reason.

ya well seen gm and other manufacturers do and engineer some real stupid stuff in my 60 yrs...
50 000 miles and 20 yrs...i'll take that any day over having to drop the tank to replace a pump. in fact when i changed the in tank pump on my stepper, was a whole day job , removing the box and what not. when i crapped out my walbro, 20 mins and i was back on the road...i'll take simpler any day

 

[Fastduramax]

Thanks Mike it's becoming a little clearer now I think, a dude pm'd me and said he wired everything through the stock dash switch which is the slickest way to go but in my case the amperage draw of the 400lph pump would likely melt that switch or worse ! So I'm assuming I need to run a Pollak 30 amp on/on separate toggle to switch the pumps and leave the stock wiring for the tank switch if that's correct ? Now did you purchase 2 pump relay wiring kits ?

 

[Hunter79764]

Thanks Mike it's becoming a little clearer now I think, a dude pm'd me and said he wired everything through the stock dash switch which is the slickest way to go but in my case the amperage draw of the 400lph pump would likely melt that switch or worse ! So I'm assuming I need to run a Pollak 30 amp on/on separate toggle to switch the pumps and leave the stock wiring for the tank switch if that's correct ? Now did you purchase 2 pump relay wiring kits ?

I'd think you would be in good shape using the factory switch to trigger a 30A relay for the pump, so that the switch is only handling the relay trigger current, which is what SquareRoot was showing on his diagram if I'm not mistaken.

 

[Fastduramax]

Right but if I remember correctly Mike is running the stock switch to operate the Pollak switching valve and gauge sending units and his diagram is actually wired to a separate toggle to chose the pump he wants to run….

 

[SquareRoot]

Right but if I remember correctly Mike is running the stock switch to operate the Pollak switching valve and gauge sending units and his diagram is actually wired to a separate toggle to chose the pump he wants to run.

Correct. I want to keep them separate for ease of troubleshooting which has come in handy. I don't mind the extra switch. I did not purchase a "kit" I just wired it up myself. A two pole switch, two BOSCH or PICO relays and 12 gauge wire is all that's needed.
I have been looking at the latest solid state relays that have multiple (4) built in relays to clean up my relay "farm". lol. I have headlight relays, fan relays, lightbar relays, door locks, alarm, etc., and I don't like how it looks. It's busy. In doing so, I was curious about the difference between the 30 and 40 amp models so, I did some fact finding.
Using my pricey Fluke multimeter I stole from work for a day, I measured the actual current on several of the circuits. Now realize there is "in rush" current that happens for a split second on startup, and then there is operating (continuous) current.
On my SPAL 11" fans the current was around 11 amps continuous per fan. On the EP381 Delphi pumps they never exceeded 5 amps. In other words, 30 amp relays are generally more than adequate for about anything one might encounter unless they start daisy chaining devices on the circuit.