Fuel pump- help

[DEEPWOODS]

Bronco is EFI with carter P4070 low pressure to BC Broncos accumulator then to ford high pressure frame rail pump. I have burned up 3 low pressure pumps in about 5 years . The high pressure won't suck through the low pump maybe because of the accumulator ? I am tired of getting stranded so what do you thing is causing the low pressure pumps to go out? I am thinking about doing away with the accumulator and low pressure and see if the high pressure pump will pickup gas and work alone. Do I need a pacific high pressure pump? Thanks for your ideas and help ,Keith

 

[SHX669]

Are the pumps burning up electrically or is the impeller " burning" up?

 

[DEEPWOODS]

I never took one apart to see. No relay or fuse problems just won't pump . It's mounted just above the rear pumpkin and high pressure is on frame rail at passenger door . I am beginning to think it has something to do with the accumulator . Every time it happens the accumulator filter is dry.

 

[AZ73]

You running a pre-filter? I'm currently building a similar set-up except using a Carter P4600HP for low pressure (it's the 3/8 version of the 5/16 P4060). You need a filter BEFORE the low pressure pump. High Pressure pumps are "pushers" not "pullers". If you want to go only High Pressure, you should put it back by the pumpkin or better yet, get an in-tank one.

You might want to read this thread:

http://classicbroncos.com/forums/showthread.php?t=227767

 

[DEEPWOODS]

Older 23 gal. Tank on this one no access for pump. I had no problem with pump when it was carburetor started when I went EFI and accumulator .

 

[toddz69]

I don't have a low-pressure pump in my system so I'm not as familiar with them but I do recall some similar failures of low pressure pumps and guys determined they needed a little more back pressure in the systems, as I recall, for them to live. It seems like maybe Dusty or others (SoCal Tom, but he's no longer on here) might know more about this.

Todd Z.

 

[Rustytruck]

My guess the low pressure pump is running full on all the time pumping fuel into the accumulator and right out the return line. Assuming that the return line is tee'd through the accumulator.

 

[DEEPWOODS]

I think the high pressure pump wont suck up fuel through the low pressure pump is because it just sucks air because of the return tee inthe accumulator dumps in the top of the tank

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[DEEPWOODS]

I know the carter low pre ssure will just run constantly. I have pulled the fuse on the high pressure pump and the low pressure pump runs constantly back to tank .I am going to pull this pump apart and try to see what is going on .

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[DEEPWOODS]

The way the accumulator is plumbed the low pressure pump circles back through the return to the tank as soon as it is full so yes it runs all the time

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[AZ73]

Ok, this made me question my initial responses so I called Carter. They basically said you don't need an accumulator for our set-up, but it won't hurt to have it. The Carter will run all the time regardless. If you have an accumulator which allows the Carter's fuel to go back to the tank, it will run like it's on an open line at 6psi unless you have a smaller return line or some other restriction. If you have no accumulator and it's just plumbed into the HP pump, it reduced the PSI to whatever the HP pump restricts the pressure draw to, and the Carter equalizes to that, meaning the vane spins, but it doesn't push any more gas than what's being used. I asked him about you going through 3 pumps in 5 years and he said he has no idea, but can't think of why the accumulator would burn your pump out unless it's letting the carter run like it's an open line with zero restrictions. The pump runs full bore all the time, but simply will stop moving fuel if the pressure in the line AFTER it is equal to the pressure it's trying to create.

 

[ntsqd]

Dusty's LP pump (A red Holley as I recall) failed somewhere on Alamo Mtn after running Miller Heep Trail (Gorman CA area) and we worked on it where Gold Hill Rd crosses Piru Creek. Most of the original SoCA Broncos guys were on that run, maybe one of them recalls what was done to fix it. I dimly recall making a bonzai run in the dune buggy out Gold Hill & back to get something from somewhere, but don't recall where or what.

I recall others having similar pump failures, but don't recall who or the circumstances. Speculation at the time was that running the pumps with no resistance wasn't good for them. Some folks added a needle valve to the system. Adding it to the return line seems like a really bad idea as that would alter the engine's AFR, but I'm not sure where they were added. The idea was that some resistance could then be added to the system so that the pump wasn't running wide open. I would suggest that a 4-6 psi pressure pop-off valve or a needle valve be added to the return port on the accumulator such that return flow from the engine to the tank is unrestricted. OR take the accumulator out of the system and simply direct-feed the HP pump from the LP pump.

If the fuel pick-up is stock or stock-like (regardless of what the tank is) then it will have a sock on the end of the pick-up. That sock is more than enough filtration for the LP pump. It is not enough for the EFI, but it is for the LP pump.

Carter pumps are particular about how they are mounted. Does yours mount with the motor down and the in/out ports above it with the cover plate roughly horizontal?

 

[DEEPWOODS]

Yes it is mounted with the motor down. The BC Broncos accumulator has a tee fitting on the top that is the return and it is plumbed per their instructions . It has no restrictions so yes it runs wide open. I have read on this forum that some say that you need 2 in and 2 out on the accumulator rather than a tee so they dislike the BC Bronco accumulator.

 

[Broncobowsher]

The Carter P4070 runs the same regardless if there is a load on it or not. It's a sliding vane pump. If there is a restriction that reaches the regulated pressure, the fuel recirculates inside the bump going through the vanes again and again. This pump runs best open ended, not restricted.

If you don't need the accumulator, just run the pump straight to the tank. The fact the high pressure pump has sucked the accumulator dry shows that it is capable of pulling fuel to itself.

If you do need the accumulator, there are some on the market that are poorly engineered. The accumulator works by running two separate loops of fuel with the accumulator as the common overlap. By getting lazy, or a poor choice of what to make an accumulator out of, putting an external T fitting in the return lines with only a single branch of the T into the accumulator you are now making a worthless accumulator. That single branch is trying to flow two directions at once, which means no flow through that line.

 

[jw0747]

Toss the low pressure pump and the accumulator. Then mount the hp pump back near the tank and you're done. Your best bet if everything is considered is to get an hp pump mounted in your gas tank even if you have to spend $ on a new tank.

 

[DEEPWOODS]

I agree with Broncobowsher about the accumulator I need to get one with 2 pipes who makes it ?

 

[Broncobowsher]

I agree with Broncobowsher about the accumulator I need to get one with 2 pipes who makes it ?

I make my own

 

[ntsqd]

I'm not sure that I agree completely with the "trying to flow two different directions at the same time" statement.

If the accumulator is low i.e. not "over-flowing", then there is no return to the tank from the accumulator and thus no flow out of the accumulator. There will be flow into it from the FPR via the return line and from the LP pump from the supply line.

If the accumulator is full then there will be flow out of it at the return fitting; and there will be flow past it from the FPR. In this instance it is more a merging flow situation. Which could cause some restriction to flow and possibly upset the AFR. Which makes a good argument for 4 total connections on top of the accumulator.

FWIW I think these "accumulators" poorly named. By design the don't/aren't supposed to hold fluid under pressure. Which is my basic understanding of an accumulator. These are better called a "reservoir", but the terminology has been wrong for too long to try to correct it now. "Reservoir" is how I view my marine spin-on fuel filter. There is no place to add the eventual return line, nor would I modify it for that. It simply is a volume of fuel that the HP pump can draw from in the event that the LP sucks air. As it happens, it is also a 4 micron fuel filter.

 

[Broncobowsher]

Two directions at the same time. Easy. You have fuel leaving the fuel rail/EFI regulator trying to get into the accumulator. At the same time fuel or air is trying to leave the accumulator. That is a flow in and a flow out both trying to go through the same line.

If both pumps are flowing the same rate and the LP starts sucking air it will fill the accumulator as the HP pump sucks it dry.

IF the HP pump flows more then the LP pump the single hose will have fuel flowing into the accumulator with no chance for air bubbles to leave as the single return line is busy refilling the accumulator with fuel off the HP loop.

If the LP pump is higher volume you have the accumulator filling with fuel and overflowing back into the main tank, like it should. The EFI return joins that return and heads to the tank as well. The single line is always exiting the accumulator. Until you start pulling air and pumping that into the accumulator. Now the EFI return is being diverted to the tank and the excess air being pumped in mixed with it. You will run as far as the EFI pump will take to dry up the accumulator.

The only reason that works halfway as good as it does for most people is the LP pump can't pump air as good as fuel. So when the LP pump starts moving air the flow in that single line goes from pushing excess fuel out to allowing EFI fuel to return in. Now you have a bit of accumulator action actually going on. Once the LP pump gets a good bite on fuel the accumulator starts filling again and the EFI return gets pushed out of the accumulator and into the return line back to the tank along with the bubble of air in the accumulator.

That is the poor engineering in putting a T fitting in the return lines on the accumulator.

Now if the overflow back to the main tank and the return off the fuel rail have separate ports on the accumulator you don't have that fight. Fuel goes in and out at whatever rate so long as there is enough flow to keep the engine feed all is happy. Any bubbles pumped in by the LP pump will perk to the top and get returned to the tank. The return off the EFI rail keeps filling the accumulator in an endless loop. Never a question if the accumulator is being pumped dry with the EFI return being diverted to the main tank by an air blockage.

 

[ntsqd]

I don't disagree that the results are wrong and undesirable, but I do think your logic in understanding or explaining what is going on is wrong. What a former supervisor of mine would cal a "violent agreement".

With fuel trying to leave the reservoir ("accumulator") by coming up the 'branch' of the 'T' and fuel trying to leave the FPR coming into one end of the 'run' of the 'T there will be two flows moving in perpendicular directions, with only one exit of the same size as the two entries. That confluence of flows is bound to cause a restriction in one or both flows, potentially upsetting the AFR. I am not convinced that 4 dedicated ports in the top of the device, vs. using a 'T', is the ultimate cure, but it is a certainly step in the right direction.

To me an accumulator is pressurized as per normal hydraulics terminology. If that is correct then this is only a reservoir.