2 fuel pumps for EFI ??????

[Michael Homan]

Way is everybody running two fuel pumps ( high volume and low volume)for the EFI systems in the EB?

Does the high volume pump not work good enough by itsself to run the fuel system?

Just a dumb buckeye here trying to get info before installing an EFI system

Thanks for any help

 

[DirtDonk]

I'm working in that direction myself, so don't know all the reasons, but I think you're meaning low and high pressure. In some setups, there is a low-pressure pump to get fuel reliably up to the high-pressure pump to feed the engine.
I believe the idea is to keep a reliable, steady supply of fuel to the high-pressure pump so it doesn't starve and shorten it's life, due to a non-baffled tank or for whatever other reasons.

Two other plumbing scenarios are 1) to use an accumulator tank to achieve the same thing, or 2) to use a specialty tank with a factory type in-tank high-pressure pump.

At least that's the scoop as I know it. Plenty of good EFI info here though, so I'm sure someone will have the exact answer for you.

Paul

 

[Michael Homan]

Thanks paul

 

[Steve83]

It's pressure - not volume.

Ford originally used both because the fuel tank sender holes weren't big enough to fit a HP pump thru. After the large hole became standard, they swapped to 1 HP pump per tank. But since the older parts are cheaper & easier to find, many people still build them that way. When I converted my '83, I used the single pump. When I did Frank's '75, I used dual (triple, actually since he has 2 tanks).

The HP in-tank pump is the best way to go, but it may take some customization on an eB tank.

 

[63A]

I'm running a low pressure/high volume pump at the tank and a high pressure pump under the hood. I used this setup to minimize the high pressure fuel line to a short section between the high pressure pump and fuel rail.

 

[00gyrhed]

I have run EFI in retro vehilces nearly every way possible. This is my fouth fuel injected antique. I have injected a 51 chevy truck, a 55 bellaire, a 350 chevy in a CJ5, and my bronco. I have tried nearly everyway you can pipe the pumps. I started doing this in 1989 on the 51. THere wasn't alot of information availble back then and most people thought I was an idiot.

First, In my 51 chevy truck (TPI) I ran and extenal tank with the High pressure pump in the external tank. The external tank was located under the main tank and pump drew fuel directly from tank behind the seat. Return went back to the tank behind the seat. This is by far the best system I ever put in. Fuel flowed from the main tank to the surge without porblems even with very dirty filters and the pump was easy to change if you needed to, but was constanly bathed in cool fuel and it ran over 150K before I took the system out and put it in my Belaire. Unfortunately you can only do it when the tank is behaind the seat.

Second, I ran a single external pump drawing diretly from tank in my 55 chevy. I ran a cheap fuel filter between the tank and the pump just to protect the pump. That senario left me road stranded more than once for several reasons. Dirty filters and dead pumps due to heat. You might be surprised how much crap thereis in pump gas.

Third, after loosing several external pumps to heat I used the same external tank from the 51 and let the HP pick fuel up out of teh 55 chevy tank. It worked good. Pumps lasted. Infact I never changed a pump once I did that, but filters between the tank and the pump were still aproblem. I just piped them where it was easy to change them and always carried a new one with me. One stop at one bad station could kill a good filter, with that set up.

Fourth, I put a 350 TPI in my CJ5. This time I was in a hurry and just cut a new hole in the top of the tank to just drop the pump in the tank. Put a sock on the pump to protect it. Worked great as long as you kept the tank more than a 1/4 full offroad. You could run the tank down to almost vapors on the street but start up a hill or off camber to the passsenger side and you would loose fuel pressure.

Fifth, I took the tank out and cut a 1-1/2" sump in the bottom and then put a 2" baffle in the tank with just a few 1/4" hoile in it and the return dumped into the sump. This set up never gave me any trouble and I ran it for almost ten years before I sold it to a buddy. He still has it and beated the crap out of it offroad. Still has the same fuel pump in it from the start. By far the best way to go. I cut an access panel in the floor of teh Jeep to allow the pump to be changed without pulling the tank. I wish I had set my Bronco up this way, I believe it to be the most reliable.

Sixth, my last FI project, my 71 bronco. I used a marine high volume 15 PSI pump to draw fuel out of the bronco tank through a filter and into a 3/4 gallon baffled surge tank I made from 6" exhaust tubing. The HP injection pump is mounted on the frame rail and draws out of the bottom of the surge tank through another filter. Return ties into the surge tank and turns down. There is also another line that allows return from the surge to the main tank. Befits of this set up are you can run the main tank completely out of fuel if you keep sloshing fuel onto the marine pump pick up. It will run a very long time without any fuel coming from the main tank. Bad things are its noisy as hell and both these pumps are susutible to heat failure. I only have about 5000 miles on this system. It is flawless except for the potential of pump falure. Good news is they are easy to find and they are both usually in stock at distribution warehouses. Bad news, if that marine pump dies on a trip it might take days to get another. I actually diconnected my marine pump and piped the external pump direct to the main tank just to see if I ought to carry a marine pump with me. The HP was able to draw fuel through a filter and run the engine just fine with 1/4 tank of gas, but offroad it burped sometimes. With more than a 1/2 tank it worked just fine. So I do not carry a spare marine pump.

 

[Bronco_69]

i used a 94 mustang sending unit and put it in the stock tank.

works great. i then bought the level sending unit for the BC tank and put it in for the level gauge.

i also used the stock fuel lines, fuel rails, and filter from a 95 big bronco. i have an OEM fuel system.

 

[jw0747]

My set-up runs a single, external HP fp mounted on the cross member near the rear tank. With this set-up, must be certain the fp is mounted lower than tank's fuel outlet because hp pumps don't have much suction power. Work's great after 3+ yrs.

In-tank fp is an excellent system but would seem very difficult to change on the trail.

 

[Broncobowsher]

If you are doing a low pressure directly into a high pressure, you are doing it wrong.

Huge factor is trying to keep the engine running when the tank is nearly out of fuel. With a carburator you can take a hard turn or accelerate quickly and the fuel pickup in the tank can suck a gulp of air, pump it through and burp it in the fuel bowl. There is fuel in the bowls and the engine will run just fine until the bowls go dry.

But injection requires steady pressure to deliver the fuel. Feed the pump one little gulp of air and the pressure drops, delivery stops, and the engine dies. There are 2 fixes for that.

The original fix was 2 pumps and an accumulator. Look on the frame rail btween the 2 pumps and you will see a plastic container with 4 lines attached. That is the factory accumulator. Takes place of the fuel bowls in the carburator.

The trouble is there are 2 pumps and extra lines, fittings, sources of leaks, and it just cost a bunch. So the engineers got crative with the in tank baffling. If you look at the bottom of the tank you will see how they catch fuel sloshing around and keep it pocketed at the pump. On very new stuff I see fuel chambers which are basicly accumulators that are open topped and overflow into the tank. The return off the regulator runs a venturi through a check valve to always keep the chamber full and overflowing. Doing this cut the system back to one pump and removed several potential sources of leaks.

The hard part about doing a single pump system that you engineer yourself is finding a way to keep the pump always sucking fuel. I have been on a trail where the rig in front dies on an uphill left tilt climb if he is under half a tank. Figured he was pulling fuel out of the left front corner of a fairly square tank. In the right attitude the inlet would go dry, pressure drop off and the engine stall. Level the rig out, it starts and runs fine. Or just keep the tank filled to the top. The fix he needed to do (don't know if he ever did) was either completely re-engineer the tank to keep fuel at the pickup or much simplier add an accumulator and a second pump.

 

[00gyrhed]

even baffles, sumps, and properly placed return lines won't match the two pump system with an accumulator for a long off camber run with a low fuel level in the tank. The sump I put in my jeep tank would be in the way in most bronco applications. You could use almost any in tank pump and and bung. You can simply hose clamp the pump to the return line from the bung. You can build a baffle to place arroud it and even cut a deep sump into the tank. even though that would be good it would not FEED the HP pump as reliably as a larger surge tank tapped at its bottom. Mine will draw fuel out of the surge until the bronco rolls over. I do not believe that any in tank set up could do that. Especially if you were close to rolling over for a long time with a low fuel level in the tank.

But there is always the fact that you have two pumps to fail, but since I can easily bypass the marine pump and still operate on the road I can live with that.

I would however probably prefer the in tank set up like I said above.

 

[Dave]

Way is everybody running two fuel pumps ( high volume and low volume)for the EFI systems in the EB?

Does the high volume pump not work good enough by itsself to run the fuel system?

Just a dumb buckeye here trying to get info before installing an EFI system

Thanks for any help

I'm using 1 in tank pump with the stock explorer collector. Here is a a link with some pictures of the tank I built.

http://classicbroncos.com/forums/showpost.php?p=1336399&postcount=108

My previous project used a stock Mustang in tank pump and has never had any fuel starvation problems without an accumulator tank unless the fuel gets below 1/4 an long hill climbs.

Unless you get creative with the fuel pickup, any system sill starve if the inlet gets uncovered and the external accumulator runs out of gas.