Making the Fuel System Simple

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TruckCo

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Good morning guys I hope everyone has a Happy Easter.

I recently dug out the squarebody. Its an 87 Dual tank with an aftermarket Pro Flo FI. I have an older truck that has just the fuel pump on the block and a single gas tank which is so simple.

I was thinking cus my truck is an 87, that is has a pickup pump in each tank. I also have the high pressure frame pump after the selector valve in between the selector valve and motor.

As i was talking to my boss about how many moving parts there are for the fuel system, he and his brother think that if i have the high pressure pump on the rail, that I dont have in tank pumps. Does anyone know if this is true? I figured the frame pump could burn out easily and would want a pony pump, but they own a ton of squarebodies so I had to think they may be right. Is there a way to test for this? Two pickup pumps, selector valve, high pressure pump? Seems like a lot of fail points to me.

Thank you!
 

Blue Ox

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Not my field, but logic suggests that if there are pumps in the tanks there will be more electrical connections than just the wire for the fuel level sender.
 
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Ricko1966

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87 should have intank pumps,and if it was mine it would still,my 86 will get them as pusher pumps when I swap tanks. Since your vehicle is far from stock fuel system wise you will have to investigate and see what p.o. has done. As for your friends building lots of square bodies, that doesn't mean they know all the changes year to the year. They may be of the mind set ,squares don't have intank pumps because non of theirs did.
 

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Can you disconnect the external pump and see if you still get fuel pressure?
 

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Your post is very confusing. You make it sound like there are 4 different fuel pumps on the truck and the fuel runs thru 3 of them at all times.
Whatever you have, the idea of having an electric pump “on the rail” or anywhere near the downstream end of the fuel system is generally bad or prohibitive. Your boss or buddy is spillin some false beans I believe.
Start by being clear what is IN your truck and what is actually being used if it has everything in your post.
 

TruckCo

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Your post is very confusing. You make it sound like there are 4 different fuel pumps on the truck and the fuel runs thru 3 of them at all times.
Whatever you have, the idea of having an electric pump “on the rail” or anywhere near the downstream end of the fuel system is generally bad or prohibitive. Your boss or buddy is spillin some false beans I believe.
Start by being clear what is IN your truck and what is actually being used if it has everything in your post.
I believe i have a in tank pump in each gas tank and then after the tank selector valve there is an electric pump on the frame .
 

Grit dog

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I believe i have a in tank pump in each gas tank and then after the tank selector valve there is an electric pump on the frame .
Gotcha. And I re-read your original post. Your mention of the mechanical pump truck is a different vehicle.
Couple things. First figure out if the in tank pumps are running/working. Suspect they aren’t or the inline pump wouldn’t be there.
You can absolutely make a permanent setup out of older style pre-efi fuel tank pickup/floats for each tank and 1 adequate fuel pump just downstream of the selector valve.
Have been running the 86 GMC for years like that now. (No fuel pump hole on the Gen vi 454) I am running a low pressure pump (because carbed) but you could do the same like you have now.
That’s about the simplest, imo, to have dual tanks and electric pump.
Couple things. Obviously keep pump as low and close to the tank(s) as possible. And if it’s not already, make sure the pump is on an ignition on relay/timer so it doesn’t just run continuously when key on.
Good luck w the project!
 

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Dragsters are known to run internal/internal or internal/external or external/external; redundant pumps.

In-tank OEM pump is preferred for a couple of reasons:

External has recommended distance BELOW AND FROM the fuel tank, for suction and back flow.

External pumps, tend to get very hot and thus the service life, can become an issue.
They tend to be noisy-er than internal pumps.

Maybe somebody disconnected the internal pumps and by-passed them, so it would be easier to change the external pump?

People ignore the distance from the tank recommendations and ignore the elevation below the tank warnings, then brag about how many years they have ignored the warnings; "it still works". Your mileage may vary, if you choose to short cut the guidelines.
You could carry a spare external pump everywhere you go, if you are too close to the tank with your external.

Internal pumps are generally preferred, because they get cooled from the returning fuel and live inside liquid.
Dropping the fuel tank to replace the internal pumps has aggravated many people into ignoring the recommendations and installing external pumps incorrectly.

Until you drop the tanks and confirm the fuel line o-rings are not square and the internal pumps have not been deleted, you are guessing at what you have.
It's important to know whether you still have fuel filter screens inside the tanks, no matter if they removed/bypassed or flow-through the internal pumps, or not.

If they disabled/removed or are flow-through the internal pumps and left the suction screens, you would still have to drop the tanks to replace the mesh intake filters and o-rings, tank seal gasket every few years. The 87' has a 3-inch x 1/4-inch giant o-ring on the tank covers and small o-rings on the OEM steel tubing lines, at every tank.

O-ring failure, the lines will suck air and cause detonation and poor running TBI. Your injectors do not like air running through them.
Neither does the TBI accelerator pump. Blocked screen intakes will eventually burn up your cavitating or fuel starved external pump too.

Tough to say what you have without pictures.

My Blazer had cut a square hole in the bed, when I bought it.
P/O cut the deck, so he could replace the fuel tank internal pump.
Least he left the internal pump location alone.

My truck was a lot cheaper than a Blazer without the hole in the floor, as a direct result of the hole-in-the-floor F/P mod.
Nobody wants to restore the rear deck from LMC, back to factory specs, after there's a 8-inch square cut into the bed.
 
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TruckCo

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Gotcha. And I re-read your original post. Your mention of the mechanical pump truck is a different vehicle.
Couple things. First figure out if the in tank pumps are running/working. Suspect they aren’t or the inline pump wouldn’t be there.
You can absolutely make a permanent setup out of older style pre-efi fuel tank pickup/floats for each tank and 1 adequate fuel pump just downstream of the selector valve.
Have been running the 86 GMC for years like that now. (No fuel pump hole on the Gen vi 454) I am running a low pressure pump (because carbed) but you could do the same like you have now.
That’s about the simplest, imo, to have dual tanks and electric pump.
Couple things. Obviously keep pump as low and close to the tank(s) as possible. And if it’s not already, make sure the pump is on an ignition on relay/timer so it doesn’t just run continuously when key on.
Good luck w the project!
Grit Dog do you think with your expierence if I “lost” the pick up pump in the tank that the Hp pump on the rail would be able to pull and still make it run to get home? I have a Pro Flo Edelbrock series FI.
 

Ricko1966

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Most newer vehicles use a pump in the tank,and some use a second external pump I can think of vehicles as early as 1985, factory with 2 pumps,an intank pusher,abd and an external pressure pump.Most vehicles with a single electric pump use in tank pumps and have for decades. There must be good reason,that every manufacturer I can think of went that route. I refuse to believe it was for assembly line productions/cost savings or they'd have skipped the in tank pump on the external pump vehicles. Some manufacturers who were external pump,just added intank pumps to their existing system. Only 2 reasons I can think of is,A.- they were bored and wanted to spend more money,or B.- it made the system more reliable. I believe the pusher pumps decrease failure on the external pump. If it were mine I'd run appropriate in tank pumps on the 87 senders,I wouldn't bother with an external pump,wire it plumb it like an 87 .
 
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wes87

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I would guess that your in tank pumps failed and the in line pump was used so they did not have to replace the in tank pumps. It is not an easy job. You can tell if your in tank pumps are working when you turn the key on. Just listen in a quiet environment. You will be able to hear them. Be quick and get under and listen at the tank or put your ear to the open fill port. If it is quiet you can hear them just standing beside the truck. If the selector valve is left, the left pump should run and vise versa for right. Easier to hear the left. Think they will run for about ten seconds to prime the system once the key is turned to the on position. If you want to change the in tank pumps it is easier to remove the bed and jack the cab up a few inches after removing the aft cab mounting bolts. My lines were way to short to drop the tank and access the lines on top to remove or replace and I have the 87 with TBI. Good luck.
 

TotalyHucked

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^That's exactly what I was going to say. My '87 IROC in HS had an external electric pump because the in tank died and the PO didn't want to replace it. If I were you, I would first contact Edelbrock to see what they recommend (if you don't have the manual for it). Afterwards, I would attempt to run it with just the in tank pumps. In tank pumps on a street vehicle are far more reliable in my experience since the fuel helps keep the pumps cool. I've had way too many friends stranded because of an external pump.
 

Grit dog

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Grit Dog do you think with your expierence if I “lost” the pick up pump in the tank that the Hp pump on the rail would be able to pull and still make it run to get home? I have a Pro Flo Edelbrock series FI.
I have not had a squarebody with in tank fuel pumps, but I believe you can pull fuel through them with another pump if they’re dead.

Presumably the inline pump is boosting pressure as I believe the Pro Flo is 55-60 psi? As stock TBI pumps don’t put out near that pressure.
So you could either be pulling through dead pumps or just boosting pressure with the inline one. IMO. But confirm.
If you want to test for sure, could unplug the fuel pump on whatever tank you’re running on and see what it does.
 

Grit dog

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And I still stand corrected as your boss could be right, and your fuel pickups could have been replaced with standard ones for a carburetor/mechanical fuel pump engine.
Either way, I believe the online pump is making the higher pressure for the pro flo. It won’t run on TBI low pressure pump. BUT you can get proper pressure in tank pumps for the higher pressure port fuel injection pressures as well.
Basically imo it’s a toss up between dual high pressure pumps in the tanks or one adequate pump plumbed in as low and close to the switching valve as possible. Reliability nudge to proper in tank pumps. Lower Cost and ease of replacement to proper inline pump only.
 
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RanchWelder

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Yes.
Yet the screens could be clogged and the o-rings flat because they have been ignored during a pull through mod, right?

Temporary fixes can burn up your engine.
 

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