Looking for a gas tank and low pressure pump

#41

[quote=“ffej” post=71530][quote=“Foglght” post=71528]So, the return line now goes directly back to the tank on the driver or passenger side?

The new setup would have the return line going to the driver side, with the output of the low pressure pump going to the return line of the passenger side high pressure pump? amirite?[/quote]

Sort of. The return line from the motor would still plug directly into the tank, you’d plug the return on the low-pressure pump and run a line from the output of the low pressure pump to the return on the high pressure pump.

At least, that’s how I see it working best. Since it’s pretty much Jim’s fix, he can tell you more.

I also think you can do this without having to completely remove the tank and disconnect everything, just lower it enough to get the fuel line from the driver to the passenger side.[/quote]
That is correct.

#42

why wouldn’t you keep the stock pump and just reroute the return line to the low pressure pump and run the transfer pump where the return line goes, unless that is in the same cavity…thus being pointless?

#43

The stock return line goes to the siphon, which is in the left side of the tank. The point of the transfer pump in the left side is to pick up fuel and drop in directly into the cup that surrounds the intake of the right side pump. The siphon works, but it’s flow rate is pretty low as compared to a transfer pump. Furthermore, the cup is roughly 1-1/4" tall so you have to keep more fuel than that in the right side to keep the cup full. In right hand turns fuel wants to slosh away from the cup and over the hump into the left side.

#44

OK, I’ve tried to follow this post, but I’m not too smart.

I have a 1987 SE30 now. This system, as I understand it, has a 55L tank, with a low pressure pump on the passenger side, a crossover tube on the bottom, and a HP fuel pump on the driver side rail somewhere next to the tank.

What I’d like to do is swap in a 63L tank, and make it so it can pick up as much fuel as possible. That said, I did not fully understand the above posts, because I don’t think anyone was doing a 55L to 63L swap in conjunction with the changes to the pump.

I apologize for being dumb, but can someone please explain exactly what I need to order and do to put a 63L tank in this 1987 and have it pick up as much fuel as possible, and hopefully have the fuel gauge still work. I would greatly appreciate it.

-Scott

#45

After doing more looking around, here is what I am thinking:

Recall that my car is a 1987.

I will put in a 88+ 63L tank.

In that 63L tank I will put 2 early low-pressure lifter / supply pumps, each feeding into a big surge tank mounted in the trunk. I will cap the return inputs on the low pressure pumps.

The surge tank in the trunk will gravity feed back to the stock high pressure pump, which will continue to feed the stock fuel rail.

The return line from the fuel pressure regulator will also feed back to the surge tank.

The surge tank overflow line will go back to the return/siphon line on the 63L tank.

A concern was raised regarding running the driver side low pressure feed pump dry, since the low pressure pump and whatever the siphon capability is will drain the left side. Is there any way to alleviate this?

Where do I put the fuel filter in this arrangement?

Where can I order two good low pressure pumps from?

Is there a way to get the fuel gauge to work with this setup?

I have to believe this setup will drink up every drop of fuel that is in the tank.

Thoughts?

#46

Jim Levie isn’t on the forum much these days and he’s the guy to talk to. Email him at jim(at)entrophy-free(dot)net

#47

There are several ways to do this, but all I will describe is the easiest and simplest.

You will need the 63L tank, the transfer pump & level sensor from a 55L system, late production high pressure pump from a 318is (it has the fuel return fitting), some hoses, connectors for the low pressure pump and level sensor, the fuel filter bracket for the 63L system (optional), and the fuel gauge from a 9/87 or later 325.

There are three minor difficulties, but all are easily dealt with. The first is that a right side level sensor is grounded, but we need to be able to wire the sensors in series. Fix this by enlarging the hole in the pump frame and the mounting holes in the sensor. Use a thicker than normal gasket (or doubled/tripled gaskets) between the sensor and pump frame, plastic sleeving over the studs, and a plastic washer under the nuts to isolate the level sensor from the tank. The second is that the mounting tabs on the left side of the tank are such that the pump frame won’t go in the way we need it to with the fittings pointed to the right. Easily fixed by taking a little material off the sides of one or two tabs (at about 5 o’clock) with a file. The last is that the early gauge expects the resistance of a single sensor. But the 63L tank needs two sensors wired in series and thus a gauge that expects the doubled resistance. Fix this by swapping the gauge in the cluster for a late 325 gauge.

You will plug the return line fitting on the transfer pump and route the output fitting to the 318’s return fitting. Returning fuel from engine bay will go to the fitting on the left side of the 63L tank. The output fitting of transfer pump takes a large hose, but the return fitting on the 318 pump takes 8mm hose. There is very little room above the tank, so use a reducer at the low pressure pump.

The rest is pretty much just splicing in the level sensor and pump wiring, putting the tank in, connecting everything up, and swapping the gauge. If you don’t use the filter bracket for the 63L system you will have to come up with a mount.

And there you go. This system will allow you to run the tank down to a just a few gallons before starvation occurs. At Roebing I ran the tank down to 2-3gal and just got a hint of starvation in turn 9 on the last lap.

#48

Jim, thanks for explaining that.

I’m not sure that I will have time for the full tank swap before the first enduro, so in the interim here is what we’re going to try.

I’m going to run the 55L tank. Someone before me monkeyed with the low pressure pump, it actually had a big walbro pump in there feeding the stock high pressure pump. They butchered the low pressure fuel pump carrier, too. What I’m doing to do is cut off everything on the carrier except the flange and the two outlet hoses. I will make up a dummy pickup from stainless steel rod that will go down until 1/4 off the floor of the tank. To that pickup on the top side I will route some fuel hose and then will mount a small 3-4 psi external in line fuel pump in the trunk. That fuel pump will feed into the side of a swirlpot. I will take the return from the fuel injectors and run that into the side of the swirlpot. The top of the swirlpot will return into the other line coming out of the flange. The bottom of the swirlpot will feed the stock external high pressure fuel pump, which I am moving to the trunk, along with the fuel filter. I will remove the pulse smoother unless someone tells me that it is a great idea to keep it.

I think this will be simple and should work. I will keep you updated. If anyone has a comment about this, I’d like to hear it.

-Scott

#49

Removing the pulse damper should be fine.

#50

You can do this and it will work, but there are a couple of concerns. Fuel pumps are generally intended to push fuel, rather than lift it. Make sure the pump you get is intended to lift fuel at least a foot. You would probably be better served by getting a new BMW transfer pump. The swirl tank needs to be metal and the hoses in the trunk need to be armored. Additionally you will have to seal the rear bulkhead with metal.

I’d suggest that you rethink this. You are going to go through a good bit of work and expense to wind up with a solution that is not as good as the 63L tank system. Also remember that the 63L tank holds an additional 2gal of fuel, which is important in an enduro that doesn’t have timed fuel stops.

#51

Jim, I hear and trust in you. This plan is already somewhat hatched, and I do have the bigger tank and will likely be doing what you suggest for the event after. Time is a factor here.

Does anybody have one or two low pressure pumps mounted on the brackets? If not, does anyone have just empty brackets?

#52

Easy… http://www.rmeuropean.com/Part-Number/Fuel-Pump-(Pre-Supply-Pump)---In-Tank-Suction-Device-__16141179415_GEN_E095124A.aspx

#53

In a stock 1989 bmw, what sits in the driver side hole of the gas tank? A low pressure feeder pump? If so, I’m guessing that this pump is deeper than the low pressure feeder pump that sits in a 1987, since the tank is deeper.

Same question on the passenger side of a 1989 bmw. I’m guessing that this is where the high pressure pump sits, and the question is, is this pump also deeper?

#54

The 63L tank has a high pressure pump and level sensor on the right (passenger) side and a level sensor in the left side. I’ve not compared the total height of a low pressure pump and the late model high pressure pump, but there can’t be much difference.

#55

OK, I’ve changed the plan once again, but I have the parts, and here is what I’m doing.

I have the 63L tank at my house, and I have dropped the 55L tank out of the car.

On the driver side of the 63L tank, I have a low pressure lift pump from the passenger side of a 1987.

On the passenger side of the 63L tank, I have just the dummy frame that used to hold a low pressure lift pump from the passenger side of a 1987. The previous owner hacked in a huge high pressure pump that won’t work, so I silver soldered on a pickup that goes to the bottom of the tank. I have an external low pressure pump that will connect to the pickup. This will function a lot like the in tank pump that is currently on the driver side, it will just have an external pump.

Both of my low pressure lift pumps will pump into a trunk mounted swirlpot. The pot will have three inlets near the top of the tank. One for each of the low pressure lift pumps, and one from the fuel rail return.

The bottom of the swirlpot will feed the stock (but now moved to the trunk) external high pressure fuel pump, which will feed fuel to the fuel rail.

The very top of the swirlpot will have either two or three fittings, and that is a question for this post. I’m going to return at least two lines, one to each return on the stock 87 style fuel pickup assemblies, so that fuel that overflows from the swirlpot is deposited right back to the low pressure lift pumps. The question is should I return three lines, with one of the lines going to the 63L siphon line on the driver side of the tank?

If not, then I plan to plug off both the driver side siphon port on the 63L tank, as well as some other small line that runs along the top of the 63L tank. I can’t see that this top line does much.

I just want to make sure that if I plug off the siphon line that is on the driver side of the stock 63L tank that the siphon still works. If not, as noted above, I will run one of the swirlpot return lines to it.

I need this car to run 2 hours without a fuel issue, and I think my solution will do just that. I’m guessing the car is going to use 8 gallons an hour, so I will need to be able to pump every drop, but I’m betting I can get close.

Let me know any general thoughts, and if anyone has specific thoughts regarding the siphon line, I’d love to hear them.

#56

Re. how many returns you have. I don’t think it matters too much. Here’s the way to think about returns…

The Return from the fuel rail needs to be able to move as much fuel as the line to the fuel rail. That means the return(s) from your swirl pot need to be capable enough that they can move as much fuel back to the tank as the high pressure pump can move from the tank.

My guess is that a nice big return from your swirl pot to either side of your tank should be adequate.

The reason for the “return must move as much fuel as the line to the rail” is that you can’t allow the fuel rail Return to become pressurized. If the fuel rail return does get pressurized then you’ll have too much fuel pressure at the injectors and 1) Their spray pattern will get hosed up and 2) The DME can only adjust for 25% too much fuel (long term fuel trim) and then the mixture will go rich on you.

#57

Use a single return from the swirl pot to the right side lift pump. The tank has a cup there for the pump pick up and it will help keep fuel feeding the pump. As compared to a lift pump, the siphon will contribute little. So I’d just plug that nipple.