Fuel starving, LP pump not picking up from main tank now

[bronco italiano]

I finally got my buddy Bronco started.

302 convert to Explorer EFI
Using Carter p4070 LP fuel pump (set within 2 feet of rear tank) and E1000 HP pump at the firewall on driver side
WH old school 23 gal tank with front fuel outlet to pump, return, fill, and vent lines on driver side frame rail.
WH accumulator between the LP and HP fuel pumps

Both pumps are turning on

Truck was idling for about 10 minutes then idle dropped and died
No fuel in the fuel rail, tried to re-prime as I initially did and hearing air when I push on the Schrader valve at the fuel rail
Fuel pressure gauge reading zero
Accumulator has fuel in the very bottom below the mount pickup tube
Manually turned on Carter LP pump with accumulator filter off and no fuel is coming through
Fuel tank was completely cleaned with 100 micron filter between tank and LP pump (Could the 100 micron filter be too small?)
Tank has about 5 gallons in it
I have spark as it was idling really nice prior to the fuel starving

 

[Broncobowsher]

Try blowing into the tank from the pickup hose at the Carter pump. There will be 3 possible results.
1) clogged
2) blows clean
3) blows bubbles in the gas tank.

After that test is done, we will know which way to proceed.

 

[lars]

Carter pumps are easy to disassemble. Have a look. I found some surprises in mine once when I had the same issue. There's a screen inside, in my case it was completely clogged. I had essentially the same arrangement as you including 100 micron filter upstream. Turned out that the fuel line between the filter and the pump broke down internally and the goop clogged the pump.

 

[bronco italiano]

Just blew into tank.

No bubbles
No blockage
Blows clean
Pick up tube fell off?

 

[Broncobowsher]

Just blew into tank.

No bubbles
No blockage
Blows clean
Pick up tube fell off?

That would be my guess as well.

Pretty much rule out the pump. If there is nothing to suck, there is nothing to pump.
If it was an old tank I could also call for a rotten pickup that now allows air to be sucked in instead of fuel.
Are you really sure there is gas in the tank? Don't those old aftermarket tanks have a drain plug?

 

[bronco italiano]

That would be my guess as well.

Pretty much rule out the pump. If there is nothing to suck, there is nothing to pump.
If it was an old tank I could also call for a rotten pickup that now allows air to be sucked in instead of fuel.
Are you really sure there is gas in the tank? Don't those old aftermarket tanks have a drain plug?

Tanks has at least 5 gallons in it as I just put it in because I had removed and completely drained the tank.
Tank does have a drain plug in the front lower corner.
Can I put a fitting at the plug and be done or should I just pull the tank and cut out the old pick up and weld in a new one.
What a PITA this build has been from day one.

 

[lars]

Bowsher has a good point. If the pickup tube is leaking/broken/whatever the pump will obviously never pull fuel. I'm guessing the truck has the same NWMP tank as I have. Sounds like if from your description. If you drop the tank and remove the sender you can see the pickup tube.

While I never had a pickup tube problem, I had plenty of other issues with my EFI fuel system which as I mentioned sounds like it was nearly identical to this one. With the additional complication of an aux tank. Last Fall after 22 years of swearing I would never switch to an in-tank pump, while ignoring the possibility that my various problems might be solved while doing so, I caved and bought in-tank kits and ISSPRO floatless senders from Tanks Inc. Capped off the NWMP pickup tube. Magic. Weird fuel starvation problems disappeared for the first time. And for the first time I can't hear a pump running. It was a lot of work but I'm glad I made the switch. And bonus points for accurated fuel gauges. If/when a pump fails I'll be hating life but hopefully that will be awhile because the pump is a Walbro.

 

[bronco italiano]

Thanks Lars,

-It is the old NWMP tank, probably more than 25 years old.
-My buddy insisted on keeping his 3 tanks (yes 3), so I had to plumb one-way check valves at each tank, vent system, and returns.
-As much as I would love to do the in-tank pumps, my buddy won't budget for that setup, so he gets the "Portuguese" setup.

 

[bronco italiano]

I am just looking like an idiot here.
Figured the fuel issue.
The return lines from EFI fuel rail was putting the fuel in the aux tank because it was closer than the main tank.
So I have a new question since my buddy has 2 aux tanks.

I want to be able to "transfer the fuel from either aux tank to the main tank via the return line.

1- I plan to use mini ball valves so only one tank can be used to transfer fuel at a time or should I allow it to feed off both tanks?
2- Is their a fuel pump better than the carter P4070 to perform the fuel transfer from both aux tanks?

 

[73azbronco]

only way to use both tanks with a return is to use an electric 8 way valve.

 

[Broncobowsher]

I want to be able to "transfer the fuel from either aux tank to the main tank via the return line.

Simple.
Set the return to the main tank only, done
Supply line to the Carter pump, pull that through a 3-way valve.
Done

When on the main tank, all normal
When on either aux tank, the return will be the transfer pump. I did this for years on a 2-tank setup. Avoided the need to put a return line to the aux tank.

The last 2-tank setup (won't work with your planned pump setup) was a high pressure on each tank that merged before the filter. When the aux tank was selected a relay would shift power from one pump to the other AND switch the low pressure 3-port selector valve that was now running backwards to select which tank the return goes to. In theory, the right 3-powition switch and a bit of wiring, you could run 3 high pressure pumps (one per tank) and a pair of 3-port electric valves and have a full electric switch 3-tank setup. The key to this all working was the high pressure pumps have a built in check valve on the outlet. To try and run this with an accumulator would get into a huge mess. I did it to a street truck. Not anything that would go off-road.